year there's a Nobel Prize and sometimes
being clueless because Georgia Tech

doesn't cover that particular field so
for example there was a Nobel Prize in

which two gentlemen diagonalize 3x3
matrix and it was a Nobel Prize we don't

work in that field but recently you know
lots of things that happen to get Nobel

Prizes we're very close to it so we were
very happy when gravitational waves were

discovered and rewarded and we're very
happy this year because this year we

have no less than three faculty who in
this field

the first speaker Richter bina he got
his degrees from Harvard and Stanford

but his PhD thesis was on measuring kind
of things that got Nobel Prize today and

you know in this larger pool of people
he was one of the leading people and one

had to choose three but you know I don't
know how it was three and Rick is not

one of them and he knows everything
about his field as well as anybody does

because he has been wizard from the very
start so Rick will start and he'll give

you some idea how this field works it's
amazing we are very we love it very much

and Rick has an online course that you
can take for free which is amazing well

if you want to get into technical
details it's it's very then our next

speakers in our gathered teeth shortened
on the as graduate students on the world

that's being rewarded today so they love
it they have it in their blood and you

will hear them explain what this work is
about so we'll start this professor

tribunal okay thank you
it's my job to give you all an ultra

short introduction to ultra-fast optics
which is perhaps most one of the most

exciting fields in all
of science today and before I get going

let me point you to my website it's
predrag mentioned WWE frog gotta do you

easy to remember and when you get there
of course you'll see the word fun and

you'll go to that site and that page and
you'll see all kinds of cool fun stuff

but then when you're done doing that
oops

you'll want to go over to talks and
there you can see all my classes and

I've got all my PowerPoint files for all
of my courses at Georgia Tech including

an entire course on ultra-fast optics
and an entire course on optics that you

can look at and they're all free and
they're all kind of like the slides if

you like the slides I have here tonight
you'll like those as well and you can

read some about something but our
research as well okay everybody in the

field of ultra-fast optics traces the
origins of the field back to an Old West

barbed at the famous robber baron Leland
Stanford made a bet with one of his

fellow robber barons they went a horse
galloped along at some point in time all

four hooves left the ground the human
eye lacked the temporal resolution to

answer that question so he had to enlist
the services of a well-known

photographer of the time Eadweard
Muybridge and that's how you spell his

name and he set up a bunch of cameras on
universe era Boulevard just there

outside of what is now Stanford
University with tripwires

and as the horse gal bye he took these
photographs with a resolution of a

sixtieth of a second and as you can see
there were definitely some times when

all four hooves left the ground and so
Stanford won the bet and hopefully it

was with that money that he was able to
form Stanford University now as I said

all all ultra-fast optical scientists
trace the origin of our field back to

this old wesbar bat and you will see as
I talk tonight even for such a short

time you will see that there's an Old
West flavor still in this field ok there

we go now we're making huge amounts of
progress and we're able to make pulses

that are much much much shorter than a
sixtieth of a second that's the temple

the length of the pulse is the temporal
resolution of our measurements and so

now you can
okay so now I guess I have to not cross

that that threshold so now we can make
pulses that are picoseconds femtoseconds

and even @o seconds long so these are
very very small numbers it's ten minus

twelve is a decimal point eleven zeros
and a one and similarly for these

quantities so these are incredibly short
events that we have no conception for

whatsoever I'll show you just how short
in a minute and then of course if we

have even a small amount of energy in
such a pulse to compute the power and we

get to divide the energy by the length
of the pulse and then that gives us a

gigantic number like terawatts and
petawatts and excellence and even even

higher these days so we're really at the
extremes of of what Sciences is about

these are the shortest events ever
created okay it's now routine to

generate pulses shorter than about 100
femtoseconds in length and researchers

generate pulses a few femtoseconds long
and even a doe seconds long and just to

give you an idea of how short such a
pulse is a 10 femtosecond light pulse is

- one minute as one minute is - the age
of the universe

oops so the question is how do we
generate such really short pulses well

it was okay well in 1916 Albert Einstein
realized that a process called

stimulated emission can occur and that
is if you have an excited molecule and

it encounters a photon of the proper
color that photon can induce that

molecule to relinquish that energy in
the form of another photon so one photon

can become - and if we pump enough
energy into the medium we call it an

excited medium and we can then generate
lots and lots and lots of photons okay

well that was back in 1916 that Einstein
realized that and it's too bad Einstein

hadn't been just a little bit smarter
because then he might have realized that

he could put a couple of mirrors it's
just very slow okay he really would have

realized that he could have put a couple
of mirrors around this and let that

process continue and continue and
continue and then we would have had a

laser it took 40 years before people
realized that you could do that

okay so what exactly how does that work
well typically inside a laser medium we

have we have our laser medium and we
have a back mirror and a front mirror

and we make the front near a little bit
less than a hundred percent reflective

so some light can get out and then we
have a pulse

oops I guess I have to be patient and
then we have a pulse that propagates

back and forth inside the laser and
every time it hits the output mirror a

little bit of it gets out of the laser
now that's really nice except it's never

quite that pretty because the pulse is
usually longer than the round-trip time

inside the laser and so then we have a
continuous beam in that case or at least

just a very long pulse and okay the
pulses that we see typically from a

laser are never really that pretty
they're always a real a real mess and

that's not exactly the kind of thing
that would be here talking to you about

tonight if that's what we always
generated so the question is how can we

then make an actual very short pulse
maybe get closer hmm so we take

advantage of a whole series of effects
in the realm of what's called nonlinear

optics where if we have a very high
intensity some interesting things can

happen that we don't ordinarily see on a
daily basis one of them is that high

intensity can turn a medium into a lens
and so that means that if we take a high

intensity beam send it into say a laser
medium maybe what'll happen is we can

experience some very tight focusing if
the intensity is high enough and if we

put an aperture in the beam at the focus
of that that lens then the entire beam

will pass through that aperture without
any of it being absorbed by the black

region the dark region opaque region of
the aperture okay on the other hand if

we have low intensity nothing happens to
the beam as you would expect and so the

beam passes through unfocused and most
of the beam is then absorbed by the

walls of the aperture okay and in that
case no focusing occurs we don't we

block most of the light okay so it turns
out that there's a particular laser

medium called titanium
fire it not only lasers but it also

exhibits strong core lensing okay and we
can see what happens if we do this

inside a laser make it a sci-fi laser
what I'll do is I'll plot the intensity

versus time of the laser no it's not as
complicated as what I showed you but it

makes the point so it's typically is
that complicated though and what happens

is this is one round-trip time and then
the next round-trip time we'll plot it a

little bit lower okay because we don't
have enough room this slide is is only

has an almost a square aspect ratio and
so what happens now is if we assume that

there's stimulated emission going on
inside the laser the amplifies pulses

but there's also this Kerr lensing
effect going on it absorbs most of the

light of weak pulses what we can see is
that as in life where the rich get

richer and the poor get poorer the
strong pulses get stronger and the weak

pulses get weaker so that's good because
that means that multiple pulses

propagating back and forth inside our
laser can turn into one pulse but more

importantly for our purposes tonight the
leading and trailing edges of the strong

pulse are also weak and so what happens
is they then get attenuated as well so

the strong pulse not only wins and
becomes the only pulse inside the laser

but it also gets shortened and every
time it goes back and forth around it

around inside the laser it gets shorter
and shorter and shorter and that's

basically all there is to it using this
trick we can make pulses 10 to the minus

14 seconds long okay not much else to it
so you now can all go home and make your

own ultra-fast laser you'll need about
$100,000 for the parts but you can do it

it's not that doesn't take a genius to
do it okay now let me tell you something

a little bit about the pulses we can
write these pulses in terms of an

intensity a center frequency and a phase
with writing the electric field now and

you've probably familiar with writing
the electric field of a light wave as a

cosine of Omega naught T as a cosine
wave or a sine wave but not we have to

take into account the fact that the
intensity of this light wave the

strength of this light wave can be
strongly peaked and beyond only on for a

short time so that's why we write the
intensity versus time here in red and

then the color can change the pulses may
be short but there's actually plenty of

time for the color to change in time so
we have to include a phase as a function

of time give you some idea as to what
this is like here's a typical pulse that

we often see in an ultra-fast optics lab
starts out red goes through all the

colors and turns out violet in the end
and that has a phase that turns out to

be an inverted parabola and it's
frequency versus time or its color

versus time is this this curve here okay
so it's an it linearly increasing plot

as you can see from the from the plot on
the left now what we really like though

is the pulse that's much more intense by
the time that's gonna say okay I'll need

about another 10 okay so what we'd
really like to do is this and that

corresponds to a flat phase and a
frequency versus time that's also flat

and I've drawn this as white because
this pulse has all the colors of the

rainbow in it so it really is white
these very short pulses really do look

white and that's the kind of pulses we
deal with not at all like what you're

used to from your normal laser pointer
days so the question we have to ask that

is how do we know how short these pulses
are cuz if you haven't measured it you

haven't made it so there's a basic
principle and that principle is that in

order to measure an event in time you
need a shorter one so let's suppose we'd

like to measure this event pretty fast
event so we need a strobe light that's

shorter than the time it takes the
bullet to go through the card but now

suppose we'd like to be able to measure
the strobe light intensity versus time

well now we need to detect or whose
response time is even faster and so on

and so on and so on until finally you
get to the shortest event ever created

how do you measure that well clearly we
need a shorter event but even more

clearly that's the one thing that we
know that we do not have so this is an

interesting dilemma and the question is
how on earth do we measure the shortest

event well in the early days of
ultra-fast optics it was realized that

another interesting domineer optical
effects could help us out here and that

is called second harmonic generation but
we take a crystal that if we send red

light into it and two pulses and those
two pulses over

and time then we get blue light okay so
there are two pulses but they didn't

overlap so you don't get blue light but
now they overlap so we get blue light

okay
they don't wanna roulette nothing they

overlap we get some blue light so all we
have to do is split our beam into

variably delay one of the pulses
relative to the other and make a plot of

how much blue light we get as a function
of the delay and we get a pretty good

idea as to how long the pulse is this
method is called intensity

autocorrelation but it's not good enough
because we're measuring the pulse width

itself it's not shorter than the pulse
okay and so what we end up with is a

blurry black-and-white picture of the
pulse and there's another problem with

autocorrelation and that is if you send
in a train of nice stable pulses I'm

plotting the intensity in the phase here
what you find is that you get a plot

like this and this is the blurry
black-and-white picture of the pulse

that I mentioned you can see it's a
little wider than these pulses are and

if there was some structure here maybe
that would wash out a little bit so it's

a somewhat broadened version of the
that's okay we can deal with that but

what we can't deal with is what happens
when each pulse is different and

complicated and then we get a trace that
looks like this which little bump

corresponds to the pulse is it the spike
on the top or the broad base but when

people first saw that they thought well
it's much more exciting to generate a

really short pulse so we'll just kind of
ignore this little base here yeah that

corresponds to the door opening when we
were making this measurement and some

light from the hallway got into the
measurement who knows what it was but

it's just some kind of back and we'll
subtract that off and this will be our

pulse length well it turns out that was
totally wrong it turns out that this

baseline is what corresponding to the
pulse and this spike which we now call

the coherent artifact is just that an
artifact that only indicates if you will

the shortest temporal structure in the
pulse which is not that interesting what

is important is how long the actual
pulse was so that was a case of

scientific self-deception and everybody
knows that and this is in the folklore

of the field of ultra-fast optics and
will be it unto him who makes that

mistake again so we all know that within
the 1960s well in an early nineteen

nineties I came along and my claim to
fame as a

scientists is I figured out how to
measure the intensity and the phase of

an arbitrary ultra short laser pulse and
interestingly it's pretty easy all we

need is these four optical elements we
use a second harmonic crystal just as

Auto correlation does but it's really
thick which violated the rules then I

can tell you all about it later but I
don't have time tonight but suffice to

say we use these four elements we don't
even need to move anything and we can

get the we can get a spectrogram of the
pulse and then we use some clever

mathematics that we borrow from the
field of astronomy and then what we find

is that this technique which we call
frequency resolved optical gating or

frog hence the website yields a
full-color high-resolution image of the

pulse and it even tells you whether
there's instability or not and it works

for all colors all intensities all
complexities of Pauls is even extremely

complex pulses so that's been a nice
thing and here is an example of a

measurement that we made just last a few
weeks of a pulse in our lab and you can

see that's the spectrogram of it and
that's the intensity and the face but

we've measured pulses that are really
really really complicated as well and it

works really well but once people
realize you could solve this problem

another technique where it's and other
techniques in fact have emerged my

favorite of which is called spider and
as you can see spider is a very

complicated method all these little
things correspond to mirrors or beam

splitters and here's an interferometer
you don't want to put interferometer and

you're in your apparatus it's really
complicated and difficult to keep

aligned and then something called the
pulse stretcher with diffraction

gratings and all kinds of other Oh
spectrometer - don't forget that so it's

a very complicated apparatus so you
might think no one's gonna use that when

they could just throw those four optical
components together and it always works

well a lot of people started using this
what's going why why is that why had all

the laser companies like this method so
much and well so we took a look I didn't

like looking at my competitors work but
we took a look and sure enough what we

found was that if you throw nice short
stable pulses into spider you get the

right answer and the guys who developed
it check that but when you throw

complicated pulses that are different
from pulse to pulse what do you know you

get that okay so spider does a good job
when the train is stable but when the

pulse changes on stage
it cannot distinguish a stable train of

short simple pulses from an unstable
train of long complex pulses well these

are the opposite cases once the
best-case scenario and the other is the

worst-case scenario so well why is that
well the only thing that Spyder measures

is the cairn artifact and so here it is
50 years later and we still have the

same the same type of mistake as people
are making there's a scientific

self-deception so if we think of this in
terms of the Old West you could argue

that the spider guys are the cattle
rustlers of the of the field they're

giving cheating a bit and and it looks
like I've won who my group is the group

that showed this where the where the
sheriff in town that has to wrestle up

the cattle rustlers and make sure things
go well because everybody wanted him a

measure a claim of shorter shorter pulse
so this is a case of self-deception and

I've made a fun list of different
self-deceptions I've become a fan of

scientific self-deceptions over the
years and the coherent artifact was a

small one from the nineteen sixties even
though everybody knows about it my

favorite one is the Piltdown man which
is an anthropological self-deception

where people in Britain dug up some
fossils they claimed to be a patient

human species but in reality we're just
a hoax but 41 years to figure that how

but and about 300 papers are written on
it but there were some distractions I

had the flu the 1918 flu was terrible
and World War one and two and the Great

Depression so we can forgive the the
anthropological community for not

knowing about about this particular host
not figuring it out but if we look at

the coherent artifact - it's been going
on for 20 years and there have been lots

of prizes and you might wonder what
distraction well how about y2k maybe

that was distracting who knows by still
going on so we're still they're still

trying to try to work on those cattle
rustlers and it's the only sell case of

self-deceptions who have been falling
for it twice and every laser company and

if you buy an ultra-fast laser they will
give you a spider measurement of the

pulse and it will be shorter than your
actual Paulson we've been working on

them and I'm just telling everybody I
mean spreading the word and most people

know it now but they're not doing much
about it okay so but we've still made a

lot of progress since then on pulse
measurement because now we measure pulse

is not just as a function of time but
also as a function

of space and here's a pulse called an
ultra-fast lighthouse that we discovered

a little while ago and here's a pulse
that's undergoing a focus and we can now

measure these as a function of space and
time and we can do it for a single pulse

we don't even need to average over a
bunch of pulses and it works really well

I'm almost done okay
and so I finest chef by saying that

there are some interesting applications
of ultra-fast optics

mine is called coherent control and
grant control is an interesting and

exciting possibility in the field of
chemistry where people will take a

molecule and you know if you have a
molecule and it undergoes some chemical

reaction nature knows what direction
wants to go in and it creates whatever

nature wants it to do but scientists
would not like to come in and bring a

shaped laser pulse in in order to cause
vibrations to occur inside that that

molecule and make the molecule
dissociate say in some way that the

scientists want not what nature wants
and if we make our pulses short enough

and and and with the right shape we can
actually do that now and there have been

hundreds of different chemical reactions
controlled in this way and maybe someday

it'll be a good way to avoid having
toxic waste in a chemical reaction or

maybe even create new chemicals that we
haven't seen before

another thing that's interesting takes
advantage of another another multi

another domineer optical effect and it's
called two photon imaging if you shine

light into a medium and look at the
fluorescence the fluorescence is maximum

at the front and it decays away kind of
exponentially as you go but if you bring

in I'm gonna hit you with the laser and
that it but if you bring in a a photon

of a much lower energy ie maybe an
infrared photon it takes two of them to

get up to the energy level that you need
to and then what happens is you only get

light fluorescing from a tiny little
spot and if you move that spot around

you can actually create really
interesting basically do microscopy and

look at all kinds of interesting images
and here's a conventional image of a

pollen grain I'm using a standard
microscope and here is a

three-dimensional image taken with this
two-photon microscopy almost every

biology lab in the world now has one of
these microscopes these images are 3d

and don't require killing and slicing up
the object in order to make a really

beautiful image and here's another image
of Amsterdam canal water and if you need

another reason not to drink Amsterdam
canal water this is it and this is in

real time at who knows what who knows
what those things are and then finally

we can make extremely clean cuts with
ultra short laser pulses here are three

examples of a continuous laser that's on
all the time a nanosecond laser which

you might think is short but no it's not
in our world it's eons and here's the

Pico second or a femtosecond laser and
what happens is the femtosecond laser

creates a little mechanical shock and
creates a nice clean cut whereas a

nanosecond laser or even longer laser
worse it has a lot of a lot of heat

dissipating all over the place as well
as shock waves and they get really nasty

looking cuts if this were the work of a
surgeon I knew this would be called a

big scar and this might be called a nice
clean cut heals really nicely and you

can do submicron sculpting with it as
well and that works to make really

beautiful things and in fact people have
been duped oops okay and then you can do

LASIK actually involves using ultra-fast
lasers as well when the little flap of

tissue has to be cut off your cornea in
order to start the LASIK process an

ultra-fast laser is also a femtosecond
lasers used typically to do that and

then you don't have to worry about the
surgeon having steady hands and cutting

this little flap off with a knife which
has been the case until just recently

and then finally another application
that is not taking off yet but there's a

group in France and Germany trying this
they've got an ultra-fast laser in a

truck and they're driving it around
looking for electrical storms and

they're shining it up into the air and
the beam is intense and it creates so

it's called an ionization path and so
that makes it a path they're the kind of

path that lightning might want to travel
and and so so they're hoping to deflect

lightning from places that you wouldn't
want lightning to hit

unfortunately it shoots the lightning it
deflects the lightning right down to the

truck hopefully they're not in the truck
when they're doing this and they have

some shield but in any case it would be
pretty

to love Sunday we could deflect
lightning away from major cities to

facilities out in the in the middle of
nowhere instead okay so with that I will

the field Chandler is a happy graduate
student playing in the left hello

so working okay can you guys hear me
back there all right okay well it's a

real pleasure to be mm to be here to be
able to give this talk Frederic thanks

for the intro I this is the first time
that I'm giving this public lecture that

the school of physics has been
organizing for some time to try to reach

out to the community and make people
aware of developments in science and

it's very exciting to be a part of that
I know that I'm looking out in the

audience and I see a lot of Georgia Tech
students but I think there are also

members from the community outside of
Georgia Tech here and so I'm really

excited to be able to to present some
science to the broader community as well

as to the students who come and take my
course so let me see how I okay so I

better my right is that so
as Rick said ultra-fast lasers were the

subject of this year's Nobel Prize in
part and Jennifer will tell you about

the other part I'm going to tell you
about the part that has to do with with

shaping laser pulses of course Rick told
you how to measure them so I'm going to

take a step back and assume that none of
you know anything about lasers or really

about
anything at all which is a perfectly

great place to start because if you
don't know anything then you won't be

mislead by anything so we all do know
what light is though light and and we've

probably probably all seen this demo
where you have a prism and you send

light into a prism and out comes a
beautiful rainbow and we all know

because we perceive colors that
different colors are making up white

light so there's something called blue
green red and we all know those things

because we see them in our eye so what
do those things have to do with light as

a wave so what is what do all waves have
in common there are many different kinds

of waves
there's there are electromagnetic waves

these are light waves but there are also
the sound waves that are propagating

across this room from me to you and
allowing you to understand what I'm

saying
there are mmm those are density waves

oscillations of the molecules in this
room there are water waves we all know

about that but what do always have in
common

there's always something that's
oscillating back and forth so if I make

a graph as a function of time there's
some quantity that's going to be going

up and down up and down up and down and
just what that quantity is varies from

one type of wave to another but there's
always something oscillating so for

light waves it's the quantity that
oscillates is the electric field and the

electric field is a little difficult to
visualize although we can visualize

light perfectly easily for sound waves
it's really the density of air molecules

in the room that's that's changing
increasing and decreasing ever so

slightly in order to convey the energy
from one place to another so the second

thing that waves have in common is they
all have some frequency of oscillation

so how many cycles of the wave that
occur in one second is known as the

frequency and for light waves that
frequency of oscillation happens to

correspond to the color of the light
wave so what we perceive as red light is

slightly lower in frequency ever so
slightly then blue light which is

slightly larger in frequency and and
don't ask me why it it appears red in

your eye I think
first debate that as well okay so for

light waves it's the electric field that
carries the energy and Rick told you a

little bit about how energy is deposited
into materials by laser light so here's

some laser light and it's an oscillating
phenomenon and now it interacts with

some molecule or some some matter and
that matter is comprised of individual

atoms that are bonded together and if
you put a little bit of light on a

molecule you can cause a chemical change
so that the light is absorbed by the

molecule and you can have things like
dissociation of the molecule or

ionization of the molecule where the
electrons on a particular atom are

stripped off so all those process is
going to happen and you might be

familiar with many of them or I've heard
of them but you may not know that the

force exerted by the light waves is
typically much much weaker than the

forces that bind this molecule together
and that's generically true but it's not

exactly intuitive to understand why it's
true how is it that something that's

really so weak and can cause the
molecule to break apart and maybe it's a

little bit like you're juggling the
molecule is really a juggling a whole

bunch of balls together and now the
light just gently tips it over so some

of them can fall out it's a very weak
process typically so I started out in

this field by trying to make that
process very strong for a little while

and then I started to make it even
weaker than it was so this is an example

of a very weak force that light can
exert on on atoms and this is something

that I do in my laboratory here at
Georgia Tech a very very weak forces of

light on atoms so here's an atom and and
here is its speed it's moving heading

towards a laser beam at 800.000 second
so we very carefully prepared the atom

so it was moving it just exactly that
speed and after it absorbs the light the

light actually exerts a tiny mechanical
for

works on the atom and pushes it a little
bit so it's now no longer moving at 800

it's moving at 799 point nine seven
meters per second so there's a very tiny

change of only three centimeters per
second that's a tiny change and it's a

super weak force and some people have
likened it to trying to slow down an

elephant with a gun that shoots only
ping-pong balls so that would take a

very long time before the elephant
recognized that you were pushing it it

would take forever almost but for atoms
it actually takes a finite amount of

time which is fortunate but there's a
real advantage to this super weak force

it's a very tiny force and that is that
once you finally do slow it down then

the force of the laser light is really
not perturbing it very much anymore and

it can be a very very gentle container
for the for the atoms so in my

laboratory here at Georgia Tech if we
can do that and slow the atoms down and

cool them and this is a little ball of
sodium atoms that are emitting beautiful

yellow light not with laser pulses but
with continuous trains of laser light I

know Rick hates those but but they are
really beautiful and the atoms here are

a thousandth of a degree above absolute
zero so they are super cold because

finally the laser light is hardly
tickling the atoms at all okay so that's

how far you can go and then if you want
to cool things even further we make

something called a bose-einstein
condensate this is a graph of of atoms

that are cooled down to even lower
temperatures of a millionth of a degree

above absolute zero so this is just an
example of how the force of laser light

can be very very weak in in its
interaction with matter so these are the

kinds of things that I study now here's
a picture of my lab so this is typically

what happens in my lab we have me
standing in the lab always know I'm

usually in my office and graduate
students this is a man beneath Carlo

Samson they were really we were really
very interested ly looking at something

that was happening in here some great
scientific discovery to be made and then

were told that someone was taking a
picture of us so immediately we got very

serious but but this is the kind of
setup that although it's it's it's not

to do with pulse lasers this is the kind
of setup that I had as a graduate

student - it's fit on an on a large
optical table there were lots of lasers

floating around and big cans in which we
had almost nothing except a few atoms

okay so coming back to the Nobel Prize
so one half of the Nobel Prize in 2018

went to Girard Maru was when I was a
graduate student a professor at the

University of Michigan in Ann Arbor
moved to France later and Donna

Strickland had worked with Gerard Moreau
at the University of Rochester and

became professor in Waterloo Canada
where she was originally from Strickland

and Meru I learned about them when I was
a graduate student doing a PhD they

invented the technique of generating
high intensity ultra short optical

pulses and we told you a little bit
about what those pulses are so I won't

dwell too much on that but what is this
discovery about and what made it

exciting and what makes it still a
little bit exciting to me is I work in

an area where we work hard in order to
to ensure that light really doesn't

perturb atoms at all so what if you went
to the other limit and you wanted to

make the light forces exceed the forces
that bind atoms together to form

molecules you might say well that's kind
of a mean thing to do you just want to

go in there and whack it and of course
if you hit it very hard it's gonna fall

apart it will it's gonna dissociate and
and all sorts of nasty things will

happen but there's actually something
subtle going on so if I want to make the

light pulse such that the force has
exceed the forces between the atoms then

the light is like a player along with
the other atoms and you can have it as

you can have a designer molecule for
instance something that is only existing

because of the light but in order to do
that the pulse duration has to be very

short otherwise you'll just blow
everything up because if the force of

the light on a molecule is stronger
than the chemical bonds then that laser

light is going to damage everything else
that's in its path because it's force is

so strong okay so in practical terms you
have to make sure that the light is only

there for a very short time and that's
in the femtosecond regime okay and for

those of you who don't know the prefixes
of the metric system in spite of Rick's

slide one millionth of one billionth of
a second so it's really very very short

by human timescales well here's the
metric system this is Rick's slide so

we're down here and these pulses that
can be generated an hour in the

attosecond range 10 to the minus 18
seconds

okay so what makes it possible to pack a
whole bunch of energy into a short pulse

is this technique that they developed
and which was honoured by the prize this

year it's called chirp pulse
amplification so I'll tell you a little

bit about that if I have enough time
okay so you start out with a short pulse

so as Rick said anybody can do it all
you need is $100,000 I don't think

that's quite the right number it's
probably more like two hundred thousand

dollars to make a short pulse oscillator
but then if you want to increase the

energy you have to amplify the laser
light which you can do using an

amplification medium but the problem is
the intensity is so high that you will

start to before you get to this regime
which you are interested in you've

already damaged all the optics in your
lab and you can't do anything so they

figure it out that well if you have a
laser then if that pulse is on for a

very short time that's the problem
because the peak intensity is very high

on the other hand if I took all of that
energy and I spread it out in time so it

was a much longer event and the peak
intensity would be lower and then I

could amplify it up to some level where
it would not damage the optics and then

if I then could recompress all of that
energy into a short pulse then the peak

intensity would be high but by then it's
already passed through all of my laser

system and it's not going to damage
anything anymore

and then that pulse can then be focused
on to the on to the atom or molecule

that I'm interested in
so it was a beautiful technique except

that the apparatus that's used to to do
this

stretching amplification recompression
it took up two optical tables and I

worked on the system just like that I
had a strickland Meru compressor

stretcher and regenerative amplifier in
my lab when I was a graduate student and

it was a finicky device so how do you
stretch it well you might think what

makes it possible for you to control
things at that temporal resolution if

it's only happening in the 100
femtoseconds how do you get in there and

stretch it out well you don't have to do
things in the time domain you can do

things in the frequency domain so this
is how it works so that light that has a

short pulse is comprised of blue light
and red light there's some blue there's

some red and if you put it onto an
object called a grating then that will

disperse the blue and red components and
if you recombine it with another grating

if you look carefully at this diagram
you'll see that the blue light which

travels through the top travels a little
bit longer path than the red light which

travels through the bottom and therefore
it gets stretched out in time okay and

so the red light hits the grady earlier
than the blue light and so if i adjust

this grating I can make the pulse
duration short and long that's just

because the light at different
frequencies all travels at the same

speed and because it travels a little
bit longer path here versus here the

pulse will get stretched out when I put
the colors back together again it's an

ingenious technique and it was something
I used as a graduate student so here's

what happens you have a very short pulse
that means there are very few

oscillations of the light of that
electric field and we put it into a

stretcher and now what comes out is
something which as I promised the red

light travelled a little bit shorter
path and the blue light so that means in

the front there's a little bit more red
light that means that the field is

oscillating a little bit more slowly
over here and it is in the back it's

traveling a little bit faster and I
found a couple of audio the same thing

works with odd
waves so it's what's called chirping

that means that the frequency here in
the front of the pulse is different from

the frequency in the back and you can
either make the frequency in the front

smaller or larger if the audio works

so that's a positive chirp for audio
waves that's a negative chair for audio

waves so we can adjust that grading so
that we either have a positive chirp or

a negative chirp we would either stretch
the pulse out or compress it back

together again so here's some data from
my PhD thesis where I had to really find

tweak that compressor I had my grading
on a translation mount and I was moving

it back and forth to make sure I got the
shortest pulse once I got the shortest

pulse I didn't have the fancy devices
that that Rick makes but but I had

something equivalent and once we have
the shortest pulse then we could make we

could measure atomic dynamics this is
actually data from my PhD thesis back

then we didn't have PowerPoint it was
about three years before PowerPoint so

this was an actual transparency that I
took up to the photocopier and

photocopied and I wrote this wrote this
with a Sharpie pen back in 1995 okay so

it's so you could you could really see
this these are ions produced by

terahertz radiation that was generated
is a very short optical pulse so the

title of my thesis read Berg wave
packets I created in in atoms I created

what are called rid berg atoms and I
excited them with half cycle pulses and

and when we had the shortest pulse then
these structures would would appear on a

timescale that was only two seconds in
duration okay all right so to conclude I

just like to tell you a little bit about
some futuristic stuff that I think is

one of the most exciting things about
about this this year's Nobel Prize is

what you can do with it okay and that is
that some people believe that you can

use really short laser pulses to probe
something called a quantum vacuum so if

you shine your laser pulse on to some
molecule which is comprised of

individual atoms then you'll whack it
and you move it around and do some fun

stuff well what if you take that same
laser pulse and you focused it into

nothing
I mean absolutely nothing you take space

and you take everything out of it
there's no more atoms or molecules there

are no cosmic rays coming in from outer
space there's nothing in there so what

happens would you expect anything to
happen so no you don't this is what the

vacuum that looks like wait that can't
be right

okay so in the vacuum is not empty so
that in what we've learned in physics

over the last 50 years is really that
the vacuum is chock-full of things that

you just can't see and you can't see
because there are so tiny there are

little little pairs of electrons and
positrons and they have an ephemeral

existence they just exist for a short
period of time and then they disappear

and they're popping up all over the
place and now what if you could take

your laser pulse and you shine it in
there and for that brief instant that an

electron-positron pair could be formed
you could strip it apart and then you

get a real particle that comes out and
if you could measure those real

particles
you'll be probing the quantum vacuum

okay so how hard is that it turns out to
be really hard okay so maybe we won't

get there but I think it could be really
exciting if we do so this is a focused

intensity in watts per square centimeter
to give you a comparison the solar

energy on the Earth's surface is 10 to
the 7 watts per square centimeter this

is to enter so there's what's called ash
ringing ten sities ten to the twenty

nine watts per square centimeter so
that's really bright it's a very bright

day if you're out in the Sun and if you
look at this intensity that people have

been able to achieve by focusing short
laser pulses using your pulse

amplification they were able to increase
the intensity quite a lot and by the

time we get to 2010 we're now at
intensities which are not anywhere near

the shrinker intensity but it turns out
that you don't have to because you can

use relativistic effects in an article
accelerator and this is the actually

reaching the regime you can bring this
down from the shrinker intensity so you

can actually probe the quantum vacuum so
with that I'll just mention that

in order to get to such high intensities
you need huge laser facilities now and

so these lasers are now much larger than
the laser I had when I was a graduate

student and I could sit there and tweak
the different parts I imagine if I went

into this laser lab and it tried to
adjust something over here I would get

kicked out pretty fast so um brick
mentioned a few brief applications I

just wanted to point out some of the
things that you might not know about so

I talked a little bit about physical
chemistry Rick did as well the dynamics

of atoms and molecules high-energy
physics creating matter from light out

of the vacuum there are also very
promising x-ray sources that you can

make which way you can create light from
light itself you can use a short pulse

nature to generate short x-ray pulses
that can be used to for example image

individual protein molecules so
potentially one could do bioimaging Rick

mentioned some of the industrial and
medical applications and then of course

because you can strip particles out of
the vacuum there's also great interest

in trying to use this for fusion energy
research and things like plasma

generation for whatever perhaps for
rescuing us from the problem of

lightning if you are interested to learn
more there's a beautiful National

Academy of Sciences report reaching for
the brightest light which details a lot

of these applications it's a little bit
technical but but it it really points

out some of the really interesting stuff
that you can do so with that I'll say

thanks and turn it over to Jennifer

so Jennifer is very similar story she
was a graduate student at the University

of Chicago and she played with optical
tweezers and they're just wonderful

beautiful thing and she'll explain why
they deserve a Nobel Prize

my laptop crashed so let me reboot it
doesn't take long I'm not sure why that

is maybe it doesn't have power

okay good

very strange didn't have any I don't
have any control I can't see my screen

and I don't have any control over my
mouse yeah I can see it on the screen

here I just can't see it on my laptop if
I unplug here hit escape it's very

strange
can't see anything

is the IT person still in the room I
just don't have any control over my I

could login if I could get to if I had
control over my keyboard but I don't you

know what I'm going to do is I'll force
shut down and reboot so I don't have it

I don't have it anywhere else but on
this laptop give me one second yeah so

okay now that I see something on my
screen I can talk while we do this so

that's a good question and it's a good
transition from dr. rahman so I remember

when I was looking to go to grad school
I knew that I wanted to study physics I

didn't know what I wanted to study so I
went to I picked a university that had

lots of options that was high quality
and I figured I'd figure it out when I

got there but the summer before the
summer before I went to grad school it

was 1997 and was that the year that the
Nobel Prize was won for bose-einstein

condensation that was but that was that
was the laser cooling and then

bose-einstein condensation was achieved
around that time and so those two things

combined made me really want to do what
Chandra does actually and so it turns

out that when I went to grad school the
University of Chicago was a great place

but they had sort of everything except
for atomic physics and so okay they had

everything except for atomic physics and
so it's sort of looking around trying to

find a lab that I wanted to work in and
David Greer's lab you'll hear a little

bit more about in my presentation I'm
almost there by the way I was working

with optical tweezers which is what I'll
tell you about today and they're just a

fantastic wonderful tool that I think
I'll convince you has entertained people

since 1986 when they were invented here
we go okay

and the good thing is is that I'm ending
this on sort of a light note with lots

of movies and lots of examples and I
think that yeah you'll see why they're

so fantastic and why people are having
fun it's interesting because I'm used to

thinking that I'm working at shortlink
scales and used to thinking that wow I

could take a tractor beam and manipulate
viruses and bacteria and cells and

that's so small but it's a whole
different game when you're competing

with the atomic physicist so and the
really ultra short laser pulses okay so

this is really all about
Ashkan and his optical trapping so

science fiction there's plenty of
examples where somehow there's some sort

of force field or electromagnetic wave
that's being used to crab onto something

you have a tractor beam and pick it up
and you can move it around I would love

for example to shine my laser beam or
some mind and force from my mind some

horse that we don't understand and pick
up dr. ramen and float him around the

room right so we all sort of have dreams
about how we might be able to do

fantastic things and especially in
manipulation and telekinesis right but

it turns out that really the Nobel Prize
that Ashkan 1/2 of is all about creating

microscopic tractor beams so we aren't
quite here okay I don't have a way that

we can pick up a person and move them
around the room but we are here where

you can take a laser beam once you've
heard all about now focus it to a tight

point and grab onto a bead which is
attached to a cell and move the cell

around and probe the cell measure
mechanics of the cell and so forth where

you could even shine that very laser
beam directly on the cell and grab onto

that cell as well that's what we refer
to as an optical tweezer an optical trap

an optical gradient trap there's lots of
different names okay but you get the

idea of tweezer it's really because it's
like having a tweezer that you can stick

into the micro or the nano and use it to
pick up something and then hold on to it

suspended in 3-d sort of levitated and
do what you like I'm going to tell you

how that works how I came about and sort
of some of the developments along the

way so this is where we are so this is
Arthur Ashe kid I think this was in his

lab in the 80s and
really his dream was to use radiation

pressure to move and manipulate objects
he knew that radiation pressure existed

but that it was a really really weak
force and so he sort of understood that

he needed to work in a regime where
other forces wouldn't damp it out he

needed to win over gravity he needed to
win over viscous damping he needed to

win over thermal forces in order to make
things happen he was at Bell Labs in the

60s where just not too long after the
laser had been invented and so he was

sitting on top of a fantastic tool to
play around with and it was in the 60s

the 70s in the 80s that he really
explored these ideas and I'll show you

his sort of series of work that got to
this his first research discovery where

he showed that he could manipulate
particles with radiation pressure was in

1970 when he was half the age he is now
so he's 96 this year he discovered this

first he showed his first proof of
principle 1975 years before I was born

and he was 48
so he's the oldest person to win the

Nobel Prize and it's been a long time
coming

so his inspiration was his understanding
their radiation pressure exists and in

fact in comments the dust tale in
particular which is comprised of neutral

objects is pushed backward by a weak
interaction with solar just solar

radiation and so he knew that there was
this possibility that light can move

matter it wasn't a new idea in fact in
the 1600s Kepler already was thinking

about the way the Sun interacted with
comets and the fact that the tails

always point away from the Sun then
James Maxwell for those of you who are

taking 2212 this semester has his
Maxwell's equations he's all about

electromagnetism and you'll get to that
at the end of the semester and he made

it formalized a theoretical prediction
of radiation pressure and basically

argued that there will be a force
imparted on any body which reflects her

flat roof racks or absorbs light okay so
it means that light can push on things

and then it was confirmed in the 1900s
that it exists experimentally so Ashkan

came into this knowing that radiation
pressure was possible that it was weak

and he just wanted to harness it right
do something with it and so there's a

few things you need to know sorry I'm
cutting in and out but I'm not sure why

there's a few things you need to know
just to understand where this

forces coming from okay so I'm gonna
remind you of a few things and go back

and forth from here to here so first of
all there's a sort of a fundamental

principle that momentum is conserved in
the universe what you may not know is

that light carries momentum so if this
was a light ray which was passing

through air and hitting this glass Pete
chunk of this chunk of glass okay

the direction that it's traveling is
also the direction of its momentum

okay so direct words the direction of
its velocity if you will okay and so the

lights momentum is related to the
direction but when the light is

reflected or refracted its momentum
changes so for example because of

Snell's law it'll Bend when it hits this
when it hits you think it's here I'm

gonna have to get to my movies when it
all experiment here I think it's about

where I'm standing not the microphone so
so see why Rick was out here so so when

it's reflected or refracted it bends
right and so if the momentum was in this

direction and now it's pointing in that
direction there's a change in the

direction of the momentum or change in
the quantity which you can calculate by

just looking at the difference between
those two vectors that change in

momentum has to be made up by somehow
and basically it's given to the glass

piece okay and so it has its own change
of momentum or if you will there's a

force that's exerted on the light that
causes it to change his momentum and due

to Newton's third law there's a force on
the glass which gives its a push and so

when you have changing momentum due to
light interactions whether it's through

absorption or whether it's due to
refraction you're going to feel it push

so we're gonna build on that in order to
understand ashcans discoveries and

inventions so his first paper from 1970
was called acceleration and trapping of

particles by radiation pressure
basically he took micron sized particles

and he accelerated them with a laser
beam and then he took two laser beams

and pointed them against each other and
he trapped the particles stabili between

those two because one was pushing this
way and one was pushing the other way so

you can dig into that paper and you can
look at the figures here's a single

laser
bean which is slightly focused with a

lens passed over some container with
little microscopic particles as

particles hop onto the beam and then
they were translated by being pushed by

the light and the key was that they were
small enough that the gravitational

force wasn't um wasn't significant
enough to pull them down out of the beam

and they still could be pushed forward
and the viscous forces from the fluid

weren't significant enough and this is a
counter-propagating dual trap beam where

they balance the particle so I have to
go over here we'll see what happens with

the microphone this is a movie which
shows a laser beam interacting with

particles and we'll see if it plays okay
I hope that doesn't happen with all of

our movies we had tested this before but
now that my computer crashed it may not

work so basically this is a laser beam
this is a particle that's hopped onto

the laser beam and if I was able to play
the movie you would see them translating

along the beam okay so a real direct
proof that there's interaction between

these things and then over here where
the beam gets weaker or you see

particles coming in and out of it they
light up but they don't go downstream

because they're it's not bright enough
to exert radiation pressure strong

enough to overcome the viscous force the
particles feel in the fluid that they're

sitting in okay so in 1986 let's see
here

was one thing that I didn't say so in
this in this invention or this first

sort of proof of principle he proved
what he expected which is that you can

use radiation pressure to push particles
around he also demonstrated that you

have to sort of work with particles that
don't create thermal heating through

absorption of the light because those
forces would swamp the radiation forces

and then lastly he observed a less
intuitive so called gradient force

that's different from the scattering
force that I was talking about which

pulls the particles to the center of the
beam so it turns out that if a particle

even gets close to the edge of the beam
it gets sucked into the middle of it

where the highest intensity is all right
so then in 1986 he started working he'd

actually
a whole bunch of stuff including work

that was developmental towards using
radiation pressure to manipulate atoms

and molecules which led on to some of
the other work that Chandra was talking

to but what was interesting was that
when he took a beam laser beam and he

focused it really strongly he expected
again just to be playing with radiation

pressure and look at the particle pop
onto the beam and flow downstream okay

but instead what he found was that the
particle traps right close to the center

of that focus and so instead of getting
blown along it got sucked under the beam

and then held right in the middle where
the focus was were actually slightly

displaced from it which wasn't expected
at all okay and so it's sort of then

that he had to sort of scratch his head
and do some thinking and some analysis

of what was going on for an accidental
discovery but it was great

because now he didn't need to counter
puppet propagating laser beams to hold a

particle in place and stabili trap
something he just needed to focus a

laser beam and at the focus an optical
particle would set and then he could use

a mirror to move the beam around and the
particle would move with no problem so

in the paper he also shows okay I think
I'm in a shout

testing let's see if this is better
alright so so in this paper he was able

to show that this trap could grab onto
particles as large as ten microns and

stabili hold on to them and go down to
25 nanometer particles so very very tiny

and this are just some schematics from
the paper we'll come back to looking at

something like this to understand how it
works this is the focus laser beam it's

going this direction there's a particle
which has been trapped at the focus and

that's why the light looks so distorted
okay alright so now I'm running out of

time and I think my favorite movie isn't
going to play for you okay so what this

movie would show you and it's really
it's really too bad that it's not going

to work is that
Ashkan sort of it's not it's not it's

not I have two minutes so alright so
anyway he was able to manipulate this

movie shows sort of the storybook of the
things you can manipulate it wasn't made

by Ashkan it was made in 2009 but it
plays with yeast it plays with bacteria

it plays with lipid vesicles and then it
goes to cells and it plays with wiggling

around the organelles in cells okay and
so now if you want to understand how the

optical trap works it basically goes
back to this idea of momentum

conservation or sort of giving a push
when light is refracted and the key is

that when you have a laser beam which is
got on bright intensity at the middle

and less intensity at the edges if the
particle is not symmetric with this this

part of the particle is encountering a
really bright intensity and so in the

when the light travels through the
particle its refracted once when it

enters and once when it leaves and so
this is the change in momentum and as a

result the particle itself feels a force
or changing momentum in the opposite

direction okay which is pushing it back
towards the center of the trap on the

other side something similar happens and
so the particle feels a force in this

way but the light isn't as bright here
as it is there so there's more force on

this side than this side so it tends to
go towards the middle if it goes too far

on the other side it's pushed back in
the other way okay so that's what it

stays in the middle
the beam and in fact that's the

explanation for what Ashkan saw
originally you can do something similar

when you deal with forces in a focused
laser beam and think about the force

that you'll get when the particles
slightly below the focus or when it's

slightly above the focus okay so it's
kind of funny I talked to chatted with

my thesis adviser and this is what he
said which I thought was kind of nice

that what really Nobel Prizes are made
of it's an obvious truth hiding in plain

sight so so applications of optical
tweezers and now I'm going to go through

these really fast because none of the
movies are going to play so manipulating

things is sort of a big thing oh look at
this it's working this is a bead

connected to two beads connected to a
strand of DNA the optical traps are

being manipulated and the DNA is being
tied in and I okay so these are sort of

a class of molecules called single
molecule experiments

lots of manipulations have been done
this is another example where the fact

that you can use an optical trap two
measures forces that are exerted on the

order of Pico Newtons and also exert
forces was used to stretch DNA okay and

I think it's gonna work all right so
anyway so what we have here is again DNA

between these two traps they're pulled
on just like this and then you can

measure the force versus stretch this is
really relevant because you have to

remember each of your cells has a small
nucleus even smaller than the cell

itself which has two meters of DNA
wrapped up and folded upon itself in

really complex ways and somehow even
with all of the folding your genetic

expression your gene expression is
working just fine and there's a lot of

mechanics involved in this optical
tweezers have also been used to grab

onto little organelles inside of your
body inside of your cells which are

attached to molecular motors which walk
around along highways in your cells and

they've been used to look at the forces
that they exert to carry the cargo it's

like an african woman carrying something
above her head they've been used to

track the steps that these motors take
to look at how much ATP conception or

energy consumption goes with that to get
the forces so this kinesin for example

takes eight nanometer steps just really
brilliant experiments when it comes to

learning about the nano scale then
the cell scale many other kinds of work

have been done taking beads which are
coated with molecules that bind to

receptors on the cell surface have been
used to present those molecules to the

cells and look at the interactions and
measure the forces between those

interactions or to look at how it
simulates cell signaling on the other

side here there's another experiment
that would never be done at the same

time a bead has been used to bind to the
cell surface and then to pull basically

the the membrane of the cell away from
an underlying network of cytoskeleton

the acting cortex I mean they measure
the force while they do that and the

force goes up and it Peaks it takes some
force to break it away and then a very

very long tube of membrane is pulled and
they measure the forces they do that and

they basically find that the force is
constant and you can pull and you can

pull and you can pull and you can pull
and you can pull and this is because the

cell has a reservoir of extra membrane
which is coming from an army of vesicles

right under the cell surface that fuse
to keep the membrane tension constant

basically there's been measurements to
look at red blood cell mechanics

anything you can imagine so I in vitro
fertilization apparently this is

actually a real technology that a
company uses you can find this online I

think my talk will be put online so I
won't show the picture or the movie and

very originally in the lab that I was in
I haven't told you what what I did we

were really interested in studying we
were really interested in studying phase

transitions and crystal growth and there
were interest that was interest in sort

of creating hundreds of optical traps to
template crystals or rearrange things in

wiggle and see how things are affected
so I'll show you one last movie and

that'll let me tell you what I do or
what I did as a graduate student so in

my lab that the question really was how
do you make hundreds of reconfigurable

optical traps in an easy way
Eric Dufresne who is a graduate student

a few years older than me had this sort
of flash of inspiration that in the same

way that light is diffracted when it
passes through a crystal and it has

spots on the wall or through a
diffraction grating you can pass a laser

beam and split it with the diffraction
grating and put points of light anywhere

you want and you can turn those points
of light

into optical tweezers and so he did that
basically I should point out an optical

trap is basically a laser beam going
into a lens and if you do it nicely you

can steer where those beams go but if
you put a diffractive optical element in

the way you can create multiple beams
that create that trap multiple objects I

came along and we started fiddling
around with basically a liquid crystal

display that acts like that diffraction
grating where you can figure out what

you need to put on it to put the traps
wherever you want and a lot of my work

was about integrating that liquid
crystal display to create hundreds of

traps this is four hundred traps well I
personally filled 200 of them that took

a while and sort of figuring out the
algorithms for how to put these things

in 2d wherever you'd like and how to do
it in 3d but the special thing is now

that this is computer addressable and
refreshable you can start moving things

around and I think this movie will work
because it's not on the web so this was

something that I made when I was a PhD
student and basically it was the first

example of dynamic holographic optical
tweezers and it was just fun because I

could basically create anything that I
wanted to create we also realized that

there's different we also made things in
3d this is not going to play and we

realized that if you change the
wavefronts of your beam or the mode of

the laser that you're working with and
you don't just work with the traditional

gaussian mode of laser beam you can do
things like put helical wave phones on

them and when you focus them instead of
looking like a spot they look like a

circle and in fact that light carries
something called orbital angular

momentum that when it interacts with
objects they spin around because the

angular momentum is transferred to the
objects so this was us playing around

with a mixture of being able to write
olicity onto our beams and then make

multiple traps simultaneously to do to
create these things so it's fun optical

traps are just something that you can
really play around with I think

generations now have enjoyed themselves
and at the same time we've really sort

of done some significant things in
dialog biology and biophysics this is

from a review paper of Ashkan just to
summarize he has a two beam trap for for

trapping his just pressure trap for
pushing his levitation trap which I

didn't talk about in the gradient trap
which is what everybody uses today

and with that we can finally have some
discussion and questions I'm responsible

for this you know I got so excited as
three people to talk think of it this

way you get three fantastic talk for the
price of one but it's running over an

hour which we hate to do please leave if
you you know have to leave what we'll do

is we'll put our speakers here they'll
sit down if anybody wants to ask a

question so if you have a question just
raise your hand and we'll bring the

microphone to you so the speakers down
front can hear regarding the short

pulses do you care about the pulse shape
at all and do you have any control over

that or just just want it as short as
possible on the other hand if you're

going to try to control a chemical
reaction then you need a very specific

pulse shape not only the intensity has
to have the correct shape but the phase

or the color versus time has to have the
correct shape so there are all kinds of

interesting applications that in fact
require very specific shapes and there

are devices that none of us talked about
called pulse shapers that allow you to

do precisely that
thanks question

maybe you answered this and I didn't
understand it but have the manufacturers

of what I think you're calling the
Spyder gotten the message

or is this second great faux pas gonna
continue on in the future and as a

corollary to that the device you
invented which seems to solve this

problem hasn't seemed to have taken off
or at least you didn't indicate that it

didn't and is that because of all the
mathematics that's involved or can you

address that also a very good question
and in fact I have given talks at almost

all the laser companies they all know
they've all read the papers and it's a

matter of someone flinching first and so
I've asked all the companies will you

please measure your pulses correctly
just go back to autocorrelation which

would give a more accurate response that
is actually sensitive to some of the

instabilities that can occur and all the
laser companies tell me the same exact

thing
we're not doing it first they said if we

have a 20 if we can claim a 25th the
second pulse we can charge $20,000 more

for our laser than if we have a 40
femtosecond pulse so it's a interesting

situation there's a lot of bad behavior
in the world and and this is an example

of it I don't think anybody's being
harmed but but people are spending more

money on lasers then then they they
really should so it's an interesting

battle to try to remove a little
self-deception from a scientific field

and it's a very common one though you
saw the list and self-deceptions that i

put on the board on the screen it
happens all the time and in fact I I was

when I first came here to Georgia Tech I
was assigned to advise an astronomer and

a new assistant professor astronomer and
I he's a brilliant guy and I asked him I

said so you know how is it in your field
how are things going and I said with my

field we have some self-deceptions he
says oh we have all kinds of

self-deceptions in our field so in
science it's very common for scientists

who believe something that's wrong you
know scientists are just people and for

example there's a famous theory of the
universe called the steady state theory

and the inventor of that theory fred
hoyle went to his death believing that

it was the correct theory it's wrong Big
Bang Theory is correct but oil you know

refused to give it up so it's a pretty
common thing in scientists are no

different from from other people we're a
little smarter but not that much smarter

the good thing is that the old men die

so they've developed the the the
microscopic earth at the tweezers right

is there work going on at Georgia Tech
enveloping products with that those

techniques there's work going on using
optical tweezers to do research but

there's not there's not further
development work I can say from my PhD

thesis and a lot of that a lot of
patents came out of it and a company was

started and they spent a lot of time
trying to sort of mark it or come up

with marketable things that optical
tweezers or holographic optical tweezers

could be used for to make money that was
an industrial scale thing or medical

scale thing and it was it was actually
kind of tricky to do so most of their

units were sold to researchers who
wanted to sort of play around in the way

hypothetical proving something or was
that you foresee some type of

application so I think that that was a
shiny side that was really literally a

shiny shiny science piece that got a
high profile paper but I think a lot of

us were scratching our heads sort of
saying what's the point but the truth is

that DNA does sometimes get tied and not
DNA mechanics since how much it can bend

and how much it stretches and so forth
really is a biophysical question that

impacts gene expression and how well
things work but that was a pretty hokey

example so I would have had to dig
deeper and have more time to give and

give sort of more I think that's an
exciting or fun example but it's not

good science example so there's other
things that you know the

the sort of central dogma is that
genetic information flows from DNA to

RNA to proteins and there's all of these
molecular machines that help go from the

DNA to then making something called RNA
and then to making protein and there's

another nice example where an RNA
polymerase that's it's a little

molecular machine moves along the DNA
and it transcribes it into the RNA which

would then later be made to protein and
so really exquisite experiments have

been done with optical tweezers to
understand exactly how the RNA

polymerase moves and what sort of what
affects it and what doesn't and this is

directly related than to gene expression
so I have a question from professor Chen

how does the you know how does this go
in top tamo twist office you know they

really do operation so tell us a little
bit you know there's a shining example

so I'm not too much of an expert on that
on that but but the kind of lasers that

go in there are actually pretty compact
and small so so the the laser system

that I used when I was a graduate
student had an oscillator that occupied

a quarter of a 5 foot by 10 foot table
and then it had some gratings which

occupied three quarters and then there
was another optical table of the same

size which had this amplifier and then
so the whole thing occupied two optical

tables but it turns out that there have
been a lot of developments on the laser

side just the oscillator part of it and
that part can actually be done using

optical fiber so the whole laser system
which I mean so the whole laser that

produces the femtosecond pulses can be
produced all within an optical fiber and

that optical fiber can just be coiled up
into a small package so that's made it

possible to to take that kind of laser
out in the lot of the out of the lab and

into the real world and that's what's
made it possible for it to have medical

applications for example so there are
some people doing research with these

very high intensity lasers to do surgery
but it's as far as I know just research

thank you very much