Good afternoon everyone. Welcome to nano tech seminar series. And we have Professor mentioned here, who's our speaker for the day. You'd like to welcome you as well as our speaker this afternoon. And I want to give a brief introduction to Professor I. Dot convention guys are pros at the Electrical and Computer Engineering at Georgia Tech else as a joint appointment at the Material Science and Engineering Department. He joined Georgia Tech in the year 20 problem and that it was postdoctoral fellow at the Stanford University where he received his bachelor's and master's degree from Tsinghua University in the year 2000 and 3000 respectively, followed by that. He did, he came to us earlier, plus B to C. This gives me the year 2008 is the research is pretty much focused on nano materials and devices. Basically. Ingratiate major impacts on the evolving field of last topics and metallic areas specifically, and guise of approximately 70 Joan learning those. And you also authored a book, optical materials fundamentals, applications. Advertises distinctions and Watson including both sides by just writing a one and the Office of Naval Research Investigator warning. So it's my pleasure to invite my colleague mentioned tied to speak on something. Seen them carry this non-linear nano contents. Don't have to come. Thank you, everyone. I do my quality and adequacy as business people in this audience. Actually, this is the very first time we have one, isn't interested in that, have us off. So I go up one. And although we probably don't have any audience in the room. So VOP to grab a lunch a lot when I say away from a file line by line, the lines relatively safely. And I know that we have other failed and the birth of a relativism. I run this. I'm going to share with you our written work on active control. Of times. It's definitely not perfect in a while. Okay? So I can offend not many people at a lot. Everyone in the audience is familiar with this nanoamperes on what case law is at all. So I think this talk, we're going to be less than N3, you one with each and every worthiness of it. So failings, Electric review, we all know this. You apply both Eva product B or E, B. And also my way the wave, so it has an ID that you own or they carry heavy metals. And the facilitator as everyone knows where. And again, omega three of these steps are that the small-scale will open up Nemo case and yet wanting not all life. And also like in action along with related pages in audio, Phoenix, different levels. What if obeys, produced by Bob is, at the very beginning, direct Bob taste with his bride for Venmo. I ended up, as I possibly can analyze any of the live, like right after my pockets. And again, that's a much more horrible thing. Metadata behind you that you describe might like adding academic way walks of life in a way. Especially electromagnetic wave, is that the witness rate or frequency range, wavelength, the problem of actual anatomy of my computer through a feel my heartbeat has not yet aware of I likely to see obey talking about AI, you can see many of my coffee plays out all your recommendations, things like that is any RIF later on how you away bikes and like that. Very complicated level, you can also use a comparable objects. We gave it a commonly occurring QED electrodynamics. Okay. Describe up the leg back, an accident happen procedure that paste it. So normally for possible packet of energy carried by NADH and Polo's hasn't been loaded from colleagues are not like us the lowest possible. And detect it gave me a time constant times the frequency. Okay. All the enemy. You didn't put a lot of mammals actually affect a fricative liable for the energy of like a lucky enough hand. They don't get out enough electrons from the cathode you enable, for example, conscience for a typo. So optics all I have an Epson is enormously important. Not only acquire within your life. And you realize, hey, I can give you a few examples. For example, for someone with almost all the lines of I offer is this device. Yeah. And most of it. These days you are brave enough to go to the movies you about. Then maybe you want to belong. We basically got up, you'll see stuff like that. And like go buy a laptop. I will see that you've set of operations, like so. You're having how they choose images. So I want to give me three dimensional perception of a disk. It's the pit and the land that you recall a binary for me. And for many CLD enticing than you are watching this lecture, somethign Internet, either love me anymore. Hi, Welcome euthanasia. Egg. They carried in optimal second-order high essence. Very, very long distance across the ocean from and we all know Zack, okay. Like laptops up getting ready. I feel satiated or one of the I suppose for renewable energy. So that's all for the luggage. And also from having any problems related to objects, not just a building they gave all case, you have a web application like the last extra enemies. And in many patients, although we all consider, only, will I see it in real life actually has enabled by objects. You need to do very complicated multi-step up, although it's our API, using systems are similar but not from big data. Then notice how in this view, utilizing to make a very small features in that for electronics. Okay, well they got us a few examples about the hierarchy of openings. And as an effort to human life. 0, 0, 0, 0, 0, 0, 0, 1 means that the behavior alive at the awakeness scale, one in the action of light medium sized when nanosized object. This is the Neolithic deposit that in how amnesty in revenue that the random number of attorneys for the metal objects basically relies on only the amorphous in theory and also the accelerations. But more importantly, as an iPhone in nanofabrication. And on Friday, we basically what it's highlighting it off, right? So nothing's working that out. In a positive 1 e of y handled. All case. It'd be the new youth and prompted for NAND gates life of union structure that metals to control time and materials. Periodic structure of the SRA Caribbean and must an order and a wavelength like this go direct to the engineered ABR response and photonic crystals. You can provide like a band gap for fourth and so on and so forth. Similar to our conventional bestows the influence, the electors and the ages in years with a handful of HIV allow us to 1948 the APA valence. I can connect to know, adjective, academic, and also it allowed us to build a heel bending out. A lot of behavioral falling in HR program, using about the refractive index is extremely large and very small enough, smaller than one. If you want a. And we have a lot of subnets y and also radiation, light. And you can rely on mental athletes to be able to very small, optional components are very tiny lasers modulators, the ACA as you actually start the saltwater. I can break it apart. And all that enormously useful. Along at a very small footprint. Very lucky or minor of his nine enamel occasionally is that now in a monetary roommate, oh, what? A minorities learner gets a lot in golden brown fat or other 999, although it happens in nonlinear media of a. So let me, the response is more profitable. Are you happy with it? So when light or in general electromagnetic wave in happy with the materials, in the material. Okay, we'll have a response, that response where we describe that UV radiation event textbook that enough aim of the key, okay? And in most materials appeal to the inactive you E of the like. But again, one of the main key on top of them to eat anymore, yeah, additional or their response. And then average it out. It'll give rise to the advocate to produce the new frequency component and an epic of life. In this case, it is very useful in many different areas in scientific research, sometimes more than we realized here, just to give you a few examples. For example, if I'm using a green laser pointer, There was a green laser pointer. That's a great list upon the others. They are, for some reason the mouse control is not working. That's why MUGA is red one. Assume they said a green laser pointer. There actually is, relies on second harmonic generation of an infrared laser. In the laser cavity of this, a green laser pointer, there is a non-linear crystal made of pB over ADP, which produces the second harmonic generation. So basically there's encountered elisa. Based on the material, the emission should be at least 1064 nanometer. Then second harmonic of that reduce wavelength by an effect by two, that will give rise to 532, which is this very broad, bright green light. Okay, is this really a very minor application? Other applications, for example, optical modulator, you know that and for the internet. For optical communications, you need to convert electrical signals to optical signals. Electrical signals are produced by your computer in the datacenter and so on. Multitiered levels of ones and zeros. And then how to convert these electrical signals to optical signals, the intensity high and the low. That relies on a very important component of so-called optical modulator. So optical modulator, this is a very typical configuration based on Mach-Zehnder interferometer. The light streaking into two halves. One army the reference that the other arm, that's a special material in the other arm so that its refractive index and therefore the interfered output through the entire device can be controlled by the applied load here signal. So this effect, refractive index, or the phase delay flight, is sensitive to the locator, basically called pockets effect vehicles, which is a second-order nonlinear optical response. And then thanks to this nonlinear optical effect, pockets effect, we can have optical modulator that they encode light with the electrical signals that eventually enable the entire Internet optical communication systems and so on. Okay. Another example, many, many different type of optical parametric processes that give rise to almost any laser wavelength we want. Conventionally be dolphin or an optics. The laser frequency, it relates to electronic transition in the material itself. For example, you have a He Ni as okay material. Then the wavelength is to obey the 632, 0.8 nanometer. You don't have much flexibility. And she knew that is covered by electronic transition intrinsic to the material. And with the optical parametric processes, basically you can have rely on the harmonic attenuation, some frequency generation, difference frequency generation, and so on. To enable the laser emission at almost any wavelets you want. Okay? And optical frequency comb basically as a broad band emission, we, the many, many spectral component evenly spaced. This optical comb can serve as a jeweler for very precise measurement. So that's the major invention. I believe. There was a Nobel prize behind that or Nobel Prize in Physics back in 2005. Okay. Optical cool. Yeah, not an optic surgery lifelong and also produce laser pulses. Typically for the health like methane, actually you need gloves with a larger instance, the intensity of light that relies on postulate is us using tooth reaching or morphine or not nowadays, okay. Mode-locked lasers. And also they said that an entire field called ultrafast optics that are relies on non-linear optics and also short laser pulses to started the mature behavior and so on. So not an object. It's also important for the generation of the terahertz wave. Terahertz wave frequency is on the order for one terahertz. In the human spectrum. Or the wavelength is on the order of say, a few micrometers or tenth of a micrometer as our handle, the macronutrient and so on. This is a previously forgotten regime in the imag spectrum, and now it's an enormously useful for both complications for national security and so on. Nine optics also give rise to better imaging behavior and the Salon because typically when you have nonlinear optical REG, inaction as more precise, more localized and also it can get into you or even body tissue and so on. So that's why we can rely on to, for the excitation microscopy to see through your skin, see inside the tissue. And another, not an optical response of a process that we use for fabrication. It's called the Q for the polymerisation. This I think as a, It's because you have a non-linear, okay, two-photon absorption so that only through this process can the polymer behavior be modified. Therefore, you can have this three-dimensional miniature, almost like sculpture or any shape you want. This is made by, I think, instrument housed in this building called a nano scribe. Yeah. Okay. So we do have data in our clean room thanks to the effort from our IN, in general. So I spent some time, you see almost a 10 or 15 minutes to cover the key word. Okay, At this moment, I assume at least you know who was optics, why it's important? What's the nano uptake? What is a nonlinear optics? Okay, now I'm going to go ahead with the more detailed relatively new scientific research that if you can understand that actually the good, otherwise as the very least, yield these, the two or three papers as the take home message. Okay, so in today's class, I'm going to knock class lecture. I'm going to discuss externally induced the neurological processes. Here you see, I believe it's the very first equation in any nonlinear optics textbook, which shows the induced polarization field in the material at a function of electric field component. For the optical wave. The first term is ruling nothing, nothing, nothing in the first field. The first component here is a typical, basically, it's just gave rise to the regular refractive index. You see this chi 11 plus tai chi one with a square root is the refractive index of the material. So the second term is called the second order nonlinear optical processes is only possible in materials to be without inversion symmetry, okay? And the second-order neuron effect is enormously important for us too. Generate a new laser component and for the active control of light through processes like tacos effect, a harmonic generation, some frequency generation difference frequency generation and so on. Thus that a term of either the third order susceptibility chi three, it's called a set order nano optical process. And it's ubiquitous because everything has a non-zero chi three other the air, okay? Not unlike a K2. In later part of my lecture, you will see we have to do a lot for taking on debt. You have neither. Okay. Tom materials and the foci three As always there, okay? And the k3 process, it important for us to say Generate and four wave mixing part. The third harmonic generation, optical Curry effect, and so on. In particular, in the past couple of years, I have been focusing on two specific 9 optical processes. One is the electrically induced second-order nonlinear optical process. So basically in the material itself doesn't know second-order susceptibility chi two intrinsically is 0 as it is for most materials. And now we can electrically induced or non-zero second-order response in the material. And also I'm going to study or describe the hot carrier, induce the active control for light, which is the third order neuron, an optical process, which can also be external induced or controlled by the flow. What dynamics of hot carriers. Okay? So this electrically induced a second-order nonlinear optical process. It's not entirely new people, new will use even since the 1960s or 1970s. So for example, it will actually control the harmonic generation. It's similar to the conventional second harmonic generation, is a 2 second order non-linear process. But a rather than a two omega photon January by omega plus omega, in this case, as by omega plus omega plus 00 means 0 frequencies. That means it's enabled or it can be influenced by our applied field. Okay? And there are many different configuration because the two January to this process, electrically induced harmonic generation. The bulk crystal summer electrolyte or liquid environment, that depletion region of a p-n junction, some 2D crystals, and some nano plasmonic systems. Okay, I have a review article focused on this. Let me show you the very first with ample wheelchairs are electrically controlled. The second-order nonlinear response from a single plasmon cavity. So this is the cavity that help you to condense light and then apply the voltage. And this controls the non-linear behaviour in our polymer, represented by this purple thing, which is a field within this nano cavity. In other, without just a very efficient the tuning of the harmonic generation for light through this gap region by the applied voltage. So there's pretty odor is certainly not exactly ten years ago pricing. Okay? And now something new. So in this part, we are trying to demonstrate to the electric controlled harmonic attenuation of light from a metal material platform. Especially here we have a metal material. So an absorber, which you can see okay, periodic and Metallica structure as the whole array in this case, separated by a backplane via direct spacer. And then you apply a voltage to enable the effective K2 response. And at the end, that can control the harmonic generation from the Intel system. So such a configuration give rise to a number of important features so that facilitate the so-called efficient electric field induced harmonics generation of light. For example, this electric or this metallic structure simultaneously support the electrical and optical functions. And there's a mathematical up top. I can light from the external world and the focus, the light into the dielectric space of which totally good, because for almost all the non optical inactions, the efficiency is proportional to the intensity of light. And also there's a nanoscale cap around here. That means when you apply a certain voltage, that's an enormous static electric field in between. So here from this octopus and e-beam images you can see, okay, this one is a cheaper be the multiple devices. This is a zoomed view of our single device. The way the electrical contact in the central region of the patent, the area look like this one. Okay? So from here you can see the IN and all our wonderful fabrication and the Nano characterization facility had been enormously beautiful for my research. Otherwise I won't possible at all. Okay? So the math material absorber as a design that you have a perfect absorption band at around the 820 nanometer. Vk is the center of our TCF laser. And from the simulation you can see, okay, like it substantially enhanced in the cavity basically by almost two orders of magnitude in terms of the intensity. In terms of field a, the wild of magnitude u squared data is two orders of magnitude. More important, the AICPA, analyzing the component of light you can see in the gap region or the field including applied field and the optical field, they are called linearly aligned along the Z direction, That's the direction perpendicular to the stack. This is the preferred configuration for the generation because in this case, if we can make use of the most pronounced the elements in this chi-squared tensor. Okay? And I believe I have to speed up because I spend too much time or the intro part to make sure that everyone at least I can understand that a few things from my talk. Okay? So here you can see, even without applied feel that you do see some harmonic generation from the system that because there's always some surface effect. And more importantly, the conversion efficiency reach the peak level at around the handle 20 nanometers. This is precisely where there's a structure is designed to function. So we are going to fix the wavelength at this excitation wavelength. Then use the rotate a level 2 Cu and harmonic generation for light from such a device from both AC and DC control. You can see that the outgoing harmonic generation is proportional to the control voltage. And this linear behavior results from actually there's some theoretical analysis and actually in our system and that's the both K3 and K2 induced by the surface structure. That is why the last term, dominance. So we have this linear response for other than solid state systems, the electric field, how many controls harmonic generation can also occur in a liquid environment, especially in some electrolyte. Because although they are applying voltage across R tiny gap, as you have seen in the previous demonstration. The strong electric field can also occur if that's a surface charge present on the metallic surface. This is direct consequence of a boundary condition of Maxwell's equation, right? If you have a row as you are going to have a very strong d of normal along the surface. Okay? So if you place a test structure in the electrode and then apply a voltage than the free ions in the liquid can flow towards get accumulated on the metallic structure. This give rise to very efficient electrical tuning of the non optical output, which is a potentially useful for biochemical sensing and the sticker no generation what signal detection in liquid environment. So the lower electrode in our configuration is that there's a hexagonal array of plasma hose. Looks simple, but when you design the experiment, thus off a few very important consideration that you have to consider. So this structure is designed that you have resonance enhance the light intensity at the wavelength of interest, in our case, around 850 or 850 nanometers in liquid solution. And the structure itself is a centrist symmetric, that means the background, the chi 2 response can be effectively suppressed. And more importantly, we need to make sure other hand the metal even forego that the metal is not consumed for the pH value and a voltage that you will use the index to an experiment. This is a pretty hot pots because actually you don't feel good if you apply the more than positive to vote towards the electrode or the gold will disappear, dissolved into the water. Okay? Suddenly we prefer to have a large area of contact between metal and the liquid along way as a good amount of fuel the announcement that overlap with the iron accumulation when a voltage is applied. Okay? So these are the major results from an experiment. Basically be applied electric potential to the electrode, to this electrode and see how the optical generation would be if affected by their behavior. Because you know that today's effective response as an enabled and therefore can be controlled by the electrical potential. Because the electric potential effects, though I'm a combination of the surface. Okay? So if you put everything in the DI water, but it doesn't know voltage-controlled a variation in the harmonic generation because there's no ions for the DI water, okay? For the electrolytes, for example, in this case I think as a potassium sulfate. Okay, for each concentration, you can see the second harmonic signal various robotically with the applied voltage with the minimum or carrying out there upon the serif HE the famous potential for 0 charge for this electrolyte system. And the tunability is pretty strong, actually, mode of magnitude stronger than what we have seen in the solid state system. Okay? More than 150 percent vote in this electrolyte solution. And also you see the change of the harmonic generation is varying quadratically with the input intensity because the standard response. And the final piece of work I'm not going to discuss in details because as almost like pure physics, because a pretty hard at the very beginning for mathematical research in a non-linear regime, there was a very famous predictions, so-called backward phase matching, also called the non-linear mirror. That means the phase match, the harmonic generation will propagate, are not collinear with the fundamental light, but rather towards the source of the fundamental light. A very exotic, unconventional behavior. And that was just a theoretical prediction onto our demonstration a few years ago. So I'm not going to discuss the details about the trick here is to enable effective response by applying a voltage across a plasmonic waveguide channel. And more importantly, we can selectively enable or disable the plasmon, increase the non-linear response in seductive a part of the waveguide, which give us extremely enjoyable flexibility in tailoring the nonlinear optical response in different part of the system. And this electrically pastor or electrically enable the K2 respond to it. Also possible in silicon and silica is important that it's simply the most important material for, for you, I believe, okay, for electronics industry, but also it's very important for photonics. Integrated circuits are largely relies on silicon-based the waveguide, like couplers and so on. And we do want to have the full function including that dynamic tuning and so on of silicon. Which is very hard because silicon has a 0 chi three. Silicon has a crystal structure which is the same as a download. The central symmetric, that means the K2 is simply 0 period. Okay? And how to enable the second-order nano optical response for the harmonic attenuation for optical rectification, for tacos effect and so on. Silicon platform. That's a possibility. How can you have the silicon? If you want to enlarge the signal, then, okay, you can also make them into a resonator, in this case a mean resonator. And then apply voltage along the static can resonate has. This will make them a very efficient and nonlinear optical resonators. And for example, we will carefully designed that and also fabricated that so that at a particular wavelength, 780 in this case, you can see perfect to me, resonating behavior to excite the magnetic dipole moment. That another figure you can see a magnetic dipole moment represented by this circling circulating electric field. And then when you vary the excitation wavelength that will fix the intensity and see the harmonic generation from tactile system. And indeed they reached the maximum, then you hit this resonance, resonance. Okay? And then in terms of a modulation without such I mean resonance, for example, for the polarization without the excitation OF MY resonance as almost an electron mobility. And for the right wavelength that together with the right excitation mode, you can see that's the harmonic generation can be very sensitive to the applied voltage as represented by these red dot. So now I'm going to switch gear to another topic, which is the optical carrier effect for all optical modulation enabled by a photoelectrons. Okay? This is the, again the stand or the very first equation for any nonlinear optics, a textbook. We discussed the first term which adjusted related to the regular refractive index. The second term is a delighted that your response okay? Like harmonic generation, optical rectification effect at some frequency generation, difference frequency generation and so on. Now let's look at the third one. There are many like an important result from this third order non-linear optical process and one of the most important one as optical Kerr effect. Optical Kerr effect means it can be viewed as like a frequency mixing behavior without changing the frequency because omega plus omega minus omega is still omega. But give rise to a direct consequence of that. He has a refractive index that is sensitive to electric field magnitude square, or the intensity of light. Okay? So the intensity is sensitive refractive index. And there are lots for major consequences from this optical Kerr effect that if there's only one BMI involved with the optical Kerr effect candies to self focusing, self, self phase modulation, modulation instability. If to be muscle control that are involved, I like this one that's a strong beam and then a weak beam. There. Apparently there's a strong beam will change the refractive index of this medium, which can be filled by a weak beam, So-called a proper BIM. Okay? So this gave rise to the so-called optical modulation. Because of the behavior of a probe, a wave will be modulated by this. A strong wave. Metals has pretty large K3 response and therefore plasmon structures and making use of metals can be can give rise to pretty good the more division tabs, along with relatively low energy, energy consumption. But on the other hand, the metals also have pretty large as thermal loading. That means the recovery of the property back to the excited state contains of cake very long time, picosecond or even longer. Let me just use another page that you introduced to you, the dynamics of. Electrons during this light matter interaction, interaction of light with the matter. We all know that metals can absorb light, especially events certain plasmonic resonance occurs. And then the incoming photons can be grabbed by the metallic structure. And then the energy can be transferred to the fourth a to the electrons. So let's take a close look at the time evolution as the very beginning. Okay, photons are absorbed here you saw some electrons again, this entity of h and knew the photon energy. And then they can reach the energy from the Fermi level. That's the initial maximum level of electrical energy to Fermi level E, f a plus a photon energy. So this happens very fast through the process of so-called that Landau damping within a 100 femtosecond. So in this case you have energetic electrons. And then in the next about a few 100 micrometers, the energetic electrons will exchange entity with the rest of electrons. And eventually all of the electrons will reach the equilibrium temporal equate the equilibrium at an elevated temperature. Okay? So they follow the Fermi distribution but at a higher temperature. So in this case a B say we have a cluster of hot electrons. So that is through electron-electron scattering, gives an even longer time when the electron you're exchanging energy visa the visa lattice through electron phonon scattering. So now electronic view further lower its temperature and increase the lattice temperature through this, the so-called the internal thermalization. And eventually, using nanosecond or even longer, the entire system will reach back to equilibrium obese the environment. Okay? So this electrodynamics is the very important for different application of hot carriers depending on your application and four, for example, many applications in photochemistry, we need to make use of the energetic electrons immediately after the Landau damping, even before a well-defined hot electron is produced. And on the other hand, for many heat related applications, the summer as a temporary response is not important at all. And for the optical modulation of the metallic property, for optical modulation itself can be relatively low because as I said, it takes the pigs can do or even longer for electron to reach equilibrium with phones through electron phonon scattering. One way for us to suppress this electron phonon scattering and speed up the response is to form a Schottky junction. For example, the metal metallic structure is the place the next two and a lecture. Electron absorb, which is some type of semiconductor and the width a Schottky junction in between. In this case, uh, we produce a one Additional channel for electron to escape. Electrode in the metal doesn't have to exchange their energy with the width of the lattice in the metal instead that they can get expelled or climb over the mountain and then reach the semiconductor. This process can be much faster than the intrinsic least allow election phonon scattering. So some general design principles. So basically we need to make sure that that's a very efficient term. Generation of hot carriers in the metal side and the junction in-between, between the metal and the electron absorber or acceptor would be, should it be appropriate so that a good amount of electron can escape because of the chest for probability it related to the function height we trade related to the relative magnitude of one electron affinity in the metal and the semiconductor and the acceptor material, we need to make sure that's sufficient. Electron density of state allowed along with the right and rely on, okay. So the first demonstration we are going to look at here is optical modulation of light using photoelectrons. So in this case, if you have this almost like a plasma and AVI is a metallic tube separated from ago, the buyer ITO layer. Then you can do the following things. First, this ITO layer, so both as a spacer and also a very good electron absorber so that the hot electron generated in these cubes can escape from the metal and enter this ITO layer. And so when certain plasmon resonance occurs, the hot electron can be generated and whether or not it escape into this ITO. The electron temperature and eventually phonon temperature can increase the intermetallic particle. Which can have an impact on the left the function of a metal. This can be seen from even the Zhou model where both the plasmonic frequency and the damping factor or related to the temperature of the electrons and the temperature of the phones. Okay? So that the mice dot structure support to resonance mode, the wire at a longer wavelength fabric polar mode, which is related to the geometry in most of the cases. And another mode that will direct you to the lattice, the lattice plasma mode. And this LP mode can be exactly the only by the TM polarized light. And its feature that with this very sharp resonance behavior. This is liquidity because this means, this. The plasmon resonance here has an, a sub gradient nature. It means so that's the radiative loss is very small so that all the incoming photons will be absorbed, hated, and almost all converted into hot electrons. So the optical modulation of the light intensity is characterized by using a probe 3 scheme. We have a broad band probe light. And then we are going to shoot to the pump light onto the structure. We should modify the electron distribution and then the Propylaia will feel the structure. And then the change in the Propylaia is characterized by the transient reflection mapping. Then we vary the time delay and also using a broadband the proper light. So it's modified by this wildcat data od, the change in the optical density. And you can see that in this case, indeed the reflection of light from this entire device, we can also translate to absorption of light can be modified by the pump light. And this horizontal axis is the wavelength of the probe light of radical via the OD. And you can see it's particularly pronounced, hits the resonance. Or by the way, we have two samples. One is based on gold and ITO, which facilitated the hockey lecture in January, can transfer the other one as the gold and the aluminum, aluminum oxide AZO to replace ITO. In this case, they are not going to allow electron transfer because the Schottky junction will be extremely large. Okay, so the linear optical response that is pretty much seminar. So any response, uh, in the dynamic translate domain can be attributed to the material difference. Okay, from this nonlinear mapping, you can see the modulation is a pretty pronounced on at the resonance. So now we do vertical cutting and see how the change in the optical behavior would be sensitive to the time delay. And you can see that in the good IT system, Aviva, hot electron generation and transport, the modulation is a very large. If you translate that data OD back to the reflection, the Cengage ammonia 80 percent. It happens within tens of no more than 200 femtosecond and then it gradually recovered. Okay, that's a very fast component which is related to hot electron transport. And a slow component trade related to the electron phonon interaction inside the metal because the electrons, photoelectrons are generated in the goat. A portion for them it can escape from the Golgi and her ITO very fast in a very small time window. And therefore the rest experience. It's a very slow process. In the control experiment where the ITO is replaced by Aluminum with a huge Schottky junction. So no electron can enter the aluminum. You can see them motivation and a much slower and also much weaker because you don't have this faster response at all. And skip this part because I mean, this pay David HER queue the entire band and the intra-band transition of a metal. And it gave rise to a different response in terms of time domain and the spectral domain. And the other then the intensity modulation. The hot electron dynamics can also help us to enable this polarization and the phase modulation of light. Because you face a is related to the refractive index, which similar to conventional optical Kerr effect that we can use a metal along with the hot electron transport to modify that, lets me just show you one selective result. Okay? So with the hot electron transport without a hydroelectric generation, basically esa output a linearly polarized light with hot electron transport within about 200 femtosecond. The polarizing light as a modified substantially. And reading about one picosecond goes back to the initial status. And without hot electron transport, the response would be much, much slower and also much, much lower, a much, much weaker. Ok. And now for the next, I have only like almost have five minutes left. So I'm going to skip a lot of Western eyes just to give you some very quick flavor about how it looks like. We can also use the hot electron, two. Enable second-order neuron optical response. Basically, your material initially be the 0 k2 response. And then now we can probably use hot lecturing to convert that into an effective second-order nonlinear media and then modify the harmonic generation and optical rectification and so on in the structure. So this is more like a motif has are described in this paper. And you can see that we have plasmonic structure and then this white seam or substrate like thing here, the titanium oxide, which the MOF ought to be the 0 k2. But, uh, When plasmon resonance occurs, then this asymmetric profile, physical profile of this, the plasma particle view give rise to the hotel actually injection, roughly falling this profile and the electron injection now enters the titanium oxide. So within a very short period, within a very short time window, we are going to can read this amorphous cadmium oxide layer initially be 0 k2 converts that into effective K2 material that to enlarge the frequency doubled output from this sculpture. And indeed from our both theoretical analysis and also experimental demonstration. You can see it's a very efficient, very effective. And the very first time that you can use another optical light, post light or see tabloid to convert a regular material into a nano optical media in the second type. And this conversion can be done as I said, in this plasmonic systems. If you want, you can also do that in two-dimensional materials because the light can be used to enable the photo excitation of electrons. So you're going to use the lights, your statuary, that some electronic transitions therefore selectively enable or disable certain Transition. In the second-order response of this, the mono layer, like a transition metal deck or a dendrite. Okay. So I believe at the time it off, so I'm going to just quickly summarize. So I believe I have convinced you that a certain plasmonic or photonic structures in general can be viewed as a self contained. The dynamic electro-optical system will be the Boesen electrical and optical functions. And such. Electrically active structure can enable a wide range of normal optical processes facilitated by an applied electric signal or the charged carriers. Okay? And we also see that optical property of metals can be modified in transit manner that give us the opportunity to control the optical behavior of a system. You are very faster transient fashion. And also we can use an optimal manner to enable the second-order neuron optical response in initially static or conventional semi-conductor. Okay, I would like to thank my collaborators to both lung and of this campus, including DOCTYPE AB on this template campus. Timberland, not in our, our campus about in this city, in Emory and also Professor Mark progress by the Stanford Shopping change. The text at a, m and z are the students who were heavily involved in the research in the past and also sometimes some of them are still in my group. Okay. And for the funding sources, of course, NSF, not just the support of my individual research program, but also a supporter days IN that'll make my research possible. And also I acknowledge the founding source from an ICA of our air for Samsung enthalpy. That's all. Thank you very much for your attention and good luck with your husband may have. Thank you. Yes. But hot electrons for example, here, it gives me no metal is not transparent. I think the beautiful idea behind all this nano photonics, many parts of augmented nano photonics, we do rely on metal, okay, we do rely on metal. If you use a piece of metal, just a uniform piece of metal that's doing nothing important because it's just like a mirror. But if we purposely structure metal into functional devices, either as individual component or as a periodic structure. So metal or not, you can really say it's opaque or not opaque or transparent. It can be transparent. It can be opaque. And you can also propose lead the line. Resonance behaviors that you control light to absorb light and so on. Yes. Thank you. And other questions, I don't think that counts the questions from the virtual space. So any questions from the lecture room audience? Mm-hm. Mm-hm. Okay. Forget MPO in optical signal processing and optical communications. Okay? Certainly each, like a secondary channel, has a dedicated wavelength. And sometimes you'll want to say that's a data series of 101, okay? Previous be carried by lambda 1 and you want another wavelength, okay? Load another wavelength, lambda 2 with this digital signal 1, 0, 1. So they can do this, okay? There's the lambda 2, you have lambda one carrying the 101. And then the ESA lambda 1 will modify the optical property of your forget an octave occur material. And then there's a lambda 2 will feel the change so that the data is now convert it from nominal one to lambda two is just a one. Layman's explanation about optical modulation. How can you mean the cafe? I talk about the three-dimensional structures, right? Either it's just, I think as a definition seeing, okay, there are different times are available in in like a light those TMD in my case, I think I'm going to okay. And there are, I think within the visible spectrum, the artery, the important message, whenever you can match one of the exotic transition, the non-optimal responses can be enlarged because from the theoretical model we can see the Chi response that is related to the transition probability of those things. Very good question. Thank you. Thank you very much. Thank you.