Good afternoon, everyone. And so what I'm going to talk, talk about today is the 24 done lithography process. So before we start, I want to see a show of hands on how many of you have actually used are aware of this. Okay, So some of you are aware of this technology. So what I'm going to talk about today is two keywords. One is rapid and others worse or dial. These two keywords are not generally used with two-photon lithography. So two-photon lithography is a nanoscale IT manufacturing technique. It's usually very, very slow and limited to a small set of materials. And what I'm going to talk about is how, how did we actually expand the material set? And the second part of the talk, and the first part I'm going to go through how did we actually scale up this process. So increase the speed by about 1000 times. Before we even go to that. What, why do we care about nanoscale already manufacturing? So these are some images of structures printed using the 24 down lithography process. Images on your left. These are structures where it will fine nanoscale feature makes a difference in the function. So the image on the top, that's an image of a architecture and material, whether density of the material changes by a factor of seven within about 100 micron thickness. And these kind of materials are very useful in controlling the pressure waves as you're compressing and material to very high pressures that inside, inside that of planets. So these are very useful for starting nuclear fusion reactions. And the second material, this material out here, this is an architect and material where because the features are so small, the flaws are smaller and the strength of this material is fairly high. And it approaches the theoretical limit of the material. But at the same time because these features are so small and most of the material is just air. The weight of the material is very low. And so we get a very strong material at a, at a very small amount of mass far the material. The other two images, images on your right. These are, these are structures where the function, functional parts are on a few micron length scale. So you need to four down lithography or something with the fine nanoscale resolution to make sure that the surfaces are smooth. Because these are either manipulating light. The surface roughness matters. Are, these are going inside human body where the surface roughness is very important. So even though the features are on the micron, single micron to ten micron size. You warn additive manufacturing on a lens scale less than a micron. Now, the process two-photon lithography, some of you have used this or are familiar with this. The processor itself is fairly straight forward toward this process. There's your take a beam of light, laser light focused into a very small spot, and then move this laser spot in 3D space within a photopolymer materials. So this photopolymer materials, when light hits this material and then density is high enough, that material is going to get converted from a liquid to a solid state. Okay? And there are chemical reactions, we will go into the details later on. But the general idea is wherever you, wherever the focus of the light hits the material that gets converted into a soldered. Now what is very, very different about this process versus other light because IT manufacturing techniques is the sub diffraction feature size. So what that means is if you take lights part, which is say, a micron wide, your printed structure can be smaller than that light spot. So that is what we mean by sub diffraction. And we'll look into the details of how do we actually get that. But the general idea is if you take a laser beam and you can move it around in space under the right conditions. You can then make these 3D structures stacking up these individual spots. So these parts are voxels or volumetric pixels. And these are some interesting structures. The GT logo, this is something we printed here using Georgia Tech's nano scribe system. The other two images are from Lawrence Livermore showing those resolution less than 150 nanometers. And you can actually print millimeter scale structures with this resolution. Now the problem with this process has been, is it's very, very slow. And if you look at the commercial capability for 24 down lithography compared with other manufacturing, R&D manufacturing techniques, there's a trade off. That trade-off is between resolution, the rate of printing, and the rate of printing of two-photon lithography. The commercial system is at least 1000 times 10 thousand times lower. And there's this uncertainty about a factor of 10 depending on how much of the material are you printing the structure, how much effort is pores? But it's 1000 or 10 thousand times slower. But what you get is very small features. And if I'm looking at this trade-off, why do I care about this? Why not just tried to push this projection micro stereolithography as far out in a resolution as I can. The reason is there's a fundamental limit based on light. Diffraction of light, okay, you cannot reduce single photon absorption, traditional light absorption, to very, very small spots below the size of the light spot. So that means that this direction improving the resolution is not, not physically a good idea. You'll hit a limit. So what we did is let's improve the rate of this process. Sorry, rate after two-photon lithography process interested in trying to reduce the resolution of traditional additive manufacturing techniques. So what we have done in the past is that red mark. There's about a 1000 times faster than commercial systems. You're still working on improving it further. And what I'm going to discuss today are some of the issues of how did we get there? What are open questions to left in this? And if I'm broadly looking at other metrics that I care about, not just the speed. There's also this metric of process knowledge and the material space that we can work in, in this process. And right now all of these are really areas where not a lot of work has been done for scalable parts. And I will, I'll go into details of what I mean by this within the context of scalability. Okay? So what we did very quickly, the results of the trooper. So in the throughput aspect, if you look at different implementations of two-photon lithography, S and P, here are serials. You take a point moved in space that serial PR parallel where you try to do multiple points simultaneously. So in the past, there used to be a trade-off, not just between two-photon lithography and other additive manufacturing techniques, but also in implementations of 24 down lithography. And this trade-off was resolution versus read. A lot of people tried making a parallel, but they feared and getting very fine features in the third dimension. Okay, so we broke this trade-off where we printed very, very thin features, at the same time printing about a 1000 times finer. Before we go into that, I wanted to spend a little bit time into the background of two-photon lithography is to how do we get these very small features, but still with light? And how can we actually get parallelization if you understand that aspect? So what is key to making 204 down lithography work is two-photon absorption, okay? So if you take traditional materials, so material on your left, traditional materials will absorb light in a single photon absorption more. So what that means is for each jump off a molecule from a lower state to a higher excited state. If you take one absorbed one photon at a time. And if you have the right photon, which means for donald the right energy to make that jump, that material will absorb light and that energy can be used for reactions downstream. For Don absorption, what happens, let's say a material wants to jump from a lower to higher state, but doesn't have the right illumination. So you don't have the right for dance. It could take 24 dance of have the energy to make that jump. Okay? Now if it does that, it needs both of these two for Don's to arrive simultaneously or near simultaneous. That happens. Then instead of a single four down, you can absorb two photons of half energy, make that jump and then use that energy downstream to do the chemical reactions. So if you're looking at just the absorption, these two look very different from a single for Don versus two for Don perspective. In a single photon absorption, most of the light is absorbed when light hits the material fast. Okay? But the focus is downstream, so the focus is right here, but most of the absorption happens at the top. Whereas in two-photon absorption, most of the absorption happens here. The focus of the lights part where the intensity is high enough because the dosage or the absorption depends on the square of intensity and the intensity is high only there. Now mathematically, if you look at the scaling of absorption words going on, is two-photon absorption is proportional to I square. It's a non-linear process and density square. And second, it's a very, very weak process. So if we take materials, regular materials and hit it with light, light from say, this projector, we don't expect materials to start absorbing in the two-photon mode. What you need is very high intensity on the order of Terra watts per centimeter square. So if you compare that to sunlight on, on Earth's surface, that's about a trillion times higher intensity. Okay? And we can get these intensities with femtosecond light, pulse light, and you focus that pulse light into a very small part, you can achieve these very high intensities. So that is the reason we need to select the right. Light source. If you take the materials that cure under light, combine the two, then we have the right conditions for 24 down lithography. Where in what you would see is that the dosage would be restricted to a small part within the light spot. Okay. So now that red region is where two up to that red curve from the center up to this point is the region where light has been absorbed into two for Don Moore. So that is smaller than this blue curve, which is actually the lights part, the intensity of light distribution. And this tells you that. Okay, So with this kind of technique, I can then confine my printing to a small spot, smaller than the light spot itself. Okay? So if we have this from a physics perspective, if you get this right, then from a, from a perspective of 3D printing, what you can now do is take this lights Parks Canada in space, 3D space within the polymer. And then stack up these individuals parts one over the other to make a 3D structure. So the differences are you can do this within the polymer itself at any depth. You're not limited to just the top. And the smallest parts are smaller than the light spot. Okay, So these are the consequences of two-photon absorption. From a manufacturing perspective. If you wanted to make a 3D part, the process flow would be, I would start with digital information. Digital information off the part that I wanted to create. So this is some kind of STL file that represents the part that you wanted to pray. Convert that into a series of toolpaths, physical spots or do you want to move the light sparked to get some of these are shown from the proprietary software for nano scribe in how you would do that using some of the software that nano scribe has. So once you convert into toolpaths, you would go into the actual system and move the light spot around to print a 3D part. Developed that what development means is your dream. Dissolve the section so the resist, the material in which you are printing, the parts which are the sections that were not exposed to light, you could dissolve this out in a solvent. So you are left with a 3D solid structure. And then you can look under different tools to verify the, the shape, size and also the material properties. Okay, So this is a fairly quick overview of two-photon lithography from the perspective of understanding the basic physics of why we get small features. And if you are able to get the right conditions, how do you make a 3D structure? The next aspect is if you compare against what the rest of the world typically does, what we have done in terms of increasing the throughput. So the rest of the world as the serial, too far down the tower, if you were to take this part and moved in space. So it's moving fairly slowly to create this 3D structure. When I see a fairly slowly hold this here. Fairly slowly is for printing about a millimeter cube, it would take anywhere from 10 hours to a 100 hours, depending on the porosity of the part. So it's fairly slow because you're printing millimeter scale structures with nanoscale a 100 nanometer features. Now in our case, what we did is we said, Let's scale this process by processing more than a single point. So process a million points at once. Okay? So what we're doing is instead of focusing a single point, we're focusing million points simultaneously where we can individually switch on and off each of these points and then focus this. But in any depth that we want within the photoresist. If you can achieve these two things, then we can do this 3D printing in a stack layers, layer by layer process where you project individual pixels of planes of pixels on each plane, where that plane is arbitrarily pattern. And then stack it up, stack up different planes to make the 3D structure. So this is very, very similar to projection stereolithography. In implementation, your project, a plain stack it up and create a 3D structure. What is different here with respect to stereo lithography is the resolution of the bar or resolution of printing. So on the, on your left, these are images. This image is from literature. Previous attempts at creating these projection type 2 photolithography implementation. So yeah. Are you able to hear me now? Okay, thanks. Okay. So the images on the image on the left, that's a projection, single projection made in the photoresist. And that projection, once you look at the party, would see that it's polymerizing everything along the depth of the photoresist. So it's not a good way of doing 3D printing. What we're getting is an extruded 2D part, which is extruded in the depth direction. What we really want is printing when you project that plane, we don't print anything above and below that plane. So that is depth resolve ability. And we were able to get that. I'll show you in a minute how we got there. If you can get this DEP resolve ability now you can print this about a micron thick layer and then keep stacking up individual layers to create your 3D structure. Okay? So some of the structures that we created were these individual nanowires which are stretched across structures which are, which would themselves printed using this process. These are some that tennis nanowires. And when I see the tennis, it's not just in plan, it's also the depth direction which has been a challenging dimension to control the other structures. Some of those micro-pillar forests that were printed in less than about two hours, when it usually takes about three days to print using the serial technique. So really fast and being able to print arbitrary patterns. And then we printed this impossible bridge, which was a very long 900 degree overhang bridge with sub-micron features and printed on a length scale of about a millimeter. So again, these are very, very challenging to print using any other technique, some other process, sorry, some other structures that would be printed. So this shows the ability to do not just grid-like structure, but also project arbitrary curved structures. So this structure again is printed using a pixelated image. I'll show you in a minute what, how we implemented this. But the idea is all of this was printed in less than 10 millisecond. So you projected a single image, had all of this patterns. And then if you want, you can stack it up in the third direction. We can also stitch these individual projections together and make millimeter scale structure is the structure on the top that took about eight minutes to print. Usually takes about a day to bring about 10 hours to a day to print depending on porosity. So how did we actually achieve this parallelization? So we achieve this parallelization by projecting an image onto the photopolymer. I'm going to skip some of the details of the optics right now. But the general idea is this is very, very similar to a projections to your lithography. This is our digital mask, which is exactly same as the mask. And here in this projector, we took that off and you hit it with light wherever you have your pixels on and off, corresponding to the on parts, you would see an image along this direction into the photopolymer. The off pixels you would see no light. So then you can project that digital information into a photopolymer and convert that into a solid part. So these two are the inputs digital information, which is any bitmap image that you can, that you want. And these two are then stacked up alternately in the third direction to create that 3D structure. Okay, So in terms of understanding what goes on in enabling us to print this large print with some micron features. So there are three steps to the process. One is when light hits the material, we need light spots that are themselves very small. So how do we focus light spots in the third dimension and in-plane? To worry very smallest parts. Second is we need to make sure that the reactions that happen when litres the material, they don't propagate out very quickly, very far. So you wanted to confine those chemical reactions. And the third is once the material has converted enough, we want to stop. And that tells us what's the size of the structure that we want. So I'm going to do very quickly go through all three of these to show you how we actually got this parallelization. So key to making this parallelization work is when we project this light into the polymer material, we wanted to make sure that the lights part is focused in the tar dimension. Getting focusing in the 2D plane is pretty straightforward. You make sure that the light focuses into very small part. Getting it focused in the third dimension is not straight forward. So what we did is we worked with the time-domain of light. So these are femtosecond light pulses. And what we did is we stretch the light pulse as it moves through the optical system and then compressor really only at the focal plane case. So if I can do this here, which is right out here away from the focal pain, I stretch the pulse out in time domain and then I compress it and stretch it again. If I can do that, then the intensity of light changes to a point that the highest density is only at the focal plane. Away from the focal plane, the density drops. And we can use that to make sure the reactions happen only near the focal plane. Okay, So that's the key to making this work in terms of projecting a large image. And also at the same time getting very, very thin light, light, light sheets, which are background. In terms of optical modelling. So it's very, very straightforward in terms of how do you staggered up. You have two lenses and your projector, the digital mask straight out from this. And a lot of people have had this question is how do we conceptualize temporal focusing? How do we conceptualize time domain focusing? And one way to understand this is if you take a femtosecond light, femtosecond light always has multiple wavelengths. It's a laser light, but it still has multiple wavelengths. When that hits a diffraction grating, then it will be split into different wavelengths. That's exactly what we do at the DMD. Or DMD is a periodic structure of mirrors. So when light hits third structure, it splits into two different wavelengths. Now if I can make sure that these different wavelengths get converge at the focal plane, then the intensity of light at the focal plane would be high. But everywhere else, because they're different wavelengths are separated out in space. The energy and the density would be low. Okay, so that's the key to making this work. Use this DMD has a diffraction grading. Make sure that all wavelengths get conversed only at the focal plane. So we were able to model this and implement this. The key thing I want to highlight here is these colored images that show the intensity of light in those colored images. So this is the light propagation direction. And I wanted to highlight is this, that the intensity of light is dropping away from the focal plane. So this is the key to making the projection technique work, because we can do that. Very little or no polymerization will happen in these kind of these regions which are away from the focus. And we could then project the image stack of different images and make it 3D bar. So this is my digital information. This is the image on the projector that gets converted into an intensity distribution which looks very, very similar to the image. And you can then stack up and make your 3D parts. I'll just briefly pause here to see if there any questions. If you have questions, feel free to stop and ask. Or we could again take it at the end too. So that was the first part, which is I project an image on the projector and then get a lighter density distribution, which is very small and small largest in the in-plane direction, but also in the third dimension, the depth direction. The next thing is we actually did the experiments and what we observed is if you wait long enough, you start getting very, very large features. So any feature below these lines, these are the only light. These are the only features that are sub diffraction. Everything else is actually bigger than the light bar. What's going on is we just we not only need very small lights parts, we also want to make sure, or we need to make sure that the reactions don't propagate out so far that you get very large structures. So the next step of the process is really this part which is often skipped in explaining two-photon lithography and explaining how do you get very small features into photolithography. So in two-photon lithography, most of the absorption is going to happen in the very small region at the focal, in the focal volume. So this is where the absorption happens. But the absorption, once the absorption happens, the material is going to start reacting through a chain reaction to form polymers. And that material is going to spread out are the polymerization front is going to spread out because it's a chain reaction if you don't stop it, if we keep expanding and without anything to stop, it will actually fill the entire volume of the resist. So what is stopping it from expanding? Is oxygen diffusing into that spot from the exterior are from the resistor itself and the oxygen is very good at terminating these chain reactions. So I'm skipping a lot of details on the chemistry part. But the, but the implication is there's this balance where the chain reaction wants to expand out the size of the part and the oxygen wants to terminate the reaction and confine the reacting part. So the balance of these two set of reaction and diffusion will determine how big a party would care. And we spent a lot of time understanding the dynamics of this in terms of the millisecond timescales it takes for it to grow. The printed voxel. And the lens scales on micron and submicron length scales. And what you observed is a lot of the reaction actually happens in their dark, which means you hit it with light. The light only last for about a 100 femtosecond. So each of these jumps, each of these jumps here is each pulse hitting the material. But all of the rest of the time is really the dark zone where there is no light. The reaction keeps proceeding in the dark. It's a chain reaction will proceed until all of the starting material. I'm Broglie seeing a starting reacting material without going into details that is used up until that happens, you will see that reaction. Eventually the size or how much the material is reacting will stabilize. So that tells us, so this kind of analysis tells us what's the feature size going to be after your project and wait for some time. So we did this kind of analysis that was very helpful and actually telling us that what happens if you wait too long, if you increase the power, Ru, change the size of the feature that you're projecting in the light sheet. And we can predict these widths very well. Our prediction of heights are not that well and we're still working on figuring out the details of this process, particularly in terms of calibrating some of the parameters are material properties of the resist. So up to this point, what I have gone through is shown you how to do the projection very quickly. So that scales up because you're going from point to a large sheet that helps us scaling up the process by a thousand times. I've also shown you that if, if you want to do that right, we need to make sure that the depth direction is well-controlled and the light sheet, and we also make sure that the resist properties that we select are such that it does not propagate too far out of the light, light, light projected region of the light spot. So the next question is, is V-star this question of scalability in terms of the rate. But there is the question of scalability in terms of how many materials can you use? And if you look into the literature, you'll see a more than 1000 papers over the past 20 years on different materials for two photolithography. Now if you look closely, what you would see is a lot of those materials cannot be used to make 3D structures. And I'll go into some of the details of what are really the issues. And even with the large literature said, why does practical ways, practical printing limited today? So if you wanted to expand the material palette from what we're doing, Let's see on the system on nano scribe here, there are three major approaches that we can take. One is weaker chain the photoresistor itself. So the photoresist may have some functional properties. And when we cure we get that function property that we care about. We could change the or we could post-process the material after printing convertible material from a polymer into some other class of material, for example, ceramics or metals. And the third approaches we could change the physical process that's happening after light hits the material. For example, instead of polymerization, we could do something else. They are different chemical reaction like reduction, and then get metallic parts instead of polymer parts. So we take the first one which is chain the photoresist. If you want to chain the photoresist, we need to Watson the photoresist. So there are four major components. Is the photo absorber that convert that light into the reactive species, which is the radicals. And then you have the pre polymer or the monomer which actually reacts and creates this polymer chain, the polymer material. The third is an additive, which could be in the form of nanoparticles that you add into the resist that are not necessarily desire, they're suspended. But once it's polymerized, you will see those additives and the part, and that will change some property, let's say electrical conductivity. And the fourth part is inhibitor, which is very, very important, which is how do you stop the reaction? Typically you will have something that, that fights with the risen to use up the radicals. Okay, so these are the four parts. If you wanted to change functional properties, we will change the pre polymer, your change this and your chain, the additives. These are the two materials you will want to change to print with a different material. So we did this. One of the approach is we said we don't want an adjective is because the issue with additives could leach out of the part after printing and development. So properties change over time. So what we said is we're going to chain the monomer and we're going to add some molecule, sorry, some atoms onto the backbone of the polymer. So we added these iodine atoms onto the backbone of the polymer itself. So once the polymer reacts to form cross-link polymer or a long chain, that iodine is in the material. And when you look at that material and our x-ray, iodine absorbs a lot of X-rays. So that part, printed part is now radiopaque. Okay? So a lot of people have done this kind of work in which they will change what is attached to the backbone. You could add in silicon, you could add in. Metal to the backbone of the polymer itself. And then you could get the property that you're looking for after printing? Yeah. Yes. So with this kind of approach, we don't see an issue which is it's homogeneous on the molecular scale. So each polymer chain will have this ratio depending on how many molecules react with each other. And so if you look at different spots, you would see you would not be able to resolve it on the feature level, on the a 100 nanometer feature level. So that is why this is a very popular approach far expanding the material set. Now what you see on this side, I've listed a lot of different things, not just the monomer. So what happens is when we start printing with different photoresist, It's not just a chemistry problem, which is, can we create a new material? It's also can we print with this new material? And I want to highlight this issue which is often ignored, which is, you'll see this tall structure here. That tall structure that's a millimeter tall structure we printed with that new resist. If you look into the literature, what you will see most of the new resist that are, that are published in papers. They're limited to about ten or ten to 50 micron heights. Okay? The reason for that is it's a challenging problem to solve for different properties of the photoresist that enable you to print in different modes and at the same time get the functionality that you want. So in this case, what we're looking for is we wanted to have this photoresist in which we have some function doped in at the same time we wanted to print millimeter scale structures. The issue is for those who have, are familiar with 24 down, you would see this aberration is a major issue in terms of printing large structures. What aberration is is if you've tried tightly focus this light spot until into a photoresist, if the refractive index of the material is not matched to the medium of the lens, to the medium that the lens was designed far, you would see these beams focusing at different planes from the focal plane. So you'd get a very large light spot instead of getting a very tight small focal spot. So what the literature has done or what researchers have done in this field is they've come up with a very clever work around what they do. They say that let's use the immersion medium for most of the light part. And right at the focus, we're going to use the resist. So this is the approach to use. The resist is only near the focal plane, but most of the light passes through the four, sorry, the immersion medium which has the right index. Now what that means is I can now print with a lot of materials. We're done. I can only print up to this height. And once I hit that height, then I cannot go any further in terms of the height of the bar. So that limits the height of the structures that we want. And nanos crime has come up with some resists that our index smashed in which you do the inverse or the upside down printing, where now the entire light, light path is within the resist, which has an index, refractive index match to the immersion medium. So now the height is not limited. You can keep building as tall as you want. There are no issues with aberration. But getting this index matching is not straightforward. So this used to be a dark heart. A lot of groups would publish, but then not tell you how to get there. So we did this experiment a thing or two years. What we figured is it's pretty straightforward. You take the photoresist or do you have a target photoresist with the function that you want? You mix it with some other photoresist that has a higher index are lower index than the target value. So if you mix and match to photoresist that have lower and higher, you'd get the index that you're looking for. So this is what you want. Mix and match something below and above that. So once we did that, now we saw the index matching issue. We have functions. We can now go and expand the material Ballard by not only having new functions, but also be able to print millimeter scale structures. So we did that for the radio pigment to you. We also did it for printing of ceramics, which is the next technique. He add some functionality into the photoresist and then you post-processor it in a way that you remove some sections of the printed, some components of the printed material. So in here we used teal, which has silicon in the backbone, and then pyrolyze this. So remove out by heat some of the carbon, oxygen and all of the hydrogen. And we're left with the ceramic silicon oxide carbide. Others have tried this out with different combinations of resists. So they also had nitrogen. So you can get a large set of ceramics by printing these polymers and then converting them into ceramics by paralyzing them. Okay? So what is key in here is it's not just converting this chemical composition, but it's also holding the geometry while this conversion happens. So that is something that makes us, or that enables us to actually print the ceramic structures additively, where you would see a linear shrinkage when some material is lost. But the relative shapes would still be the same. Can still make these complex 3D structures in ceramics by printing something which is larger and with something which has polymer reactive components so it polymerizes. The third approach is so you can chain the photoresist Eigen post-process. But I could also change the chemical reactions that are happening under the influence of light. And one example is this photo reduction, which is instead of having these chemicals react to create long polymer chains, I start with the salt of a metal. When light hits that material, that salt has reduced intermetallic particle nanoparticle. So this is very commonly done for mirror making with silver. And if we can replicate that using the light, light projection of this technique, we can then have a high-speed projection of metallic nanoparticles and stack up. So, so far what we have shown is we can do this using the serial technique at a high speed by moving this part in space. You can move it in 3D space, which is these silver particles, nanoparticles printed on top of existing structures to make these 3D metallic structures. So up to this point, what I've shown, you just go through this and then we'll switch over. So these are some examples of structures printed with the metallic structures. So we can print these grid lines, at least could also be functional structures where the diffraction grading showing a diffraction pattern when light goes through it. And the conductivity of these materials is fairly good, about 1 fifth of the bulk silver. So you could then start making 3D structures which are both conductive and maybe even composites with polymers and metallic sections in there. So what I've shown you so far is scaling up in terms of the speed, scaling up in terms of the materials said. And now very briefly I wanted to show you. So the open questions in two-photon lithography and just looking at it from the perspective of generations of growth in this field, what has really happened is if you look on the process knowledge axis, about 20 years ago, this process was invented where a light spot was mode in space very slowly and a 3D part was buried. Or the next two generations, the speed of that part has been increased by 1000 times. Our work has scaled it up farther by a thousand times by parallelizing this process. But simultaneously, we have also lost a lot of process knowledge are really not necessarily lost, but the process knowledge has really expanded to a point where we only know a little bit, a little fraction of it. Because of which we are not able to do any of this deterministic printing of parts. And for those who have actually printed parts and nanos crime, they even know this issue, which is, let's say I want a 3D part that I wanted to print. What I do is I start with an STL. We'll print. So the question is what parameters do a print width, which is if you're doing a serial words thorough speed at which you're going to move, Javier, going to discretize or break it up into voxels, and what power are you going to use? So these questions have not yet been answered properly in the literature, which means I take some guesses. Print the bar, compare the print against this TA to see how close am I to that. And keep repeating this loop. And I iteratively, if I'm guessing it right, or after certain number of iterations, I would arrive at a set of conditions that give me the part that I want. So this is very slow, very expensive. But the experience you will see it takes a lot of time to get particular functional part. What we want to do is convert this into deterministic process. Where you know enough about the process that you go in with your STL, you figure out what your input should be, provide that input. And with the foster run, you'd get parts to specifications. We are nowhere near that. And some of the work we're doing with the NSF Career Award project is this, figuring out the process knowledge gaps that tell us how to deterministically print apart based on this STL. So this should be the inputs that you want to give it. I'm going to stop here. We'll just comment that the processor itself is not scalable both from a materials perspective and also from a trooper perspective. But we don't know enough about the process to a point that we can deterministically make part. So applying it to real-world applications is still challenging due to a large process knowledge gap. And before I stop, I would like to thank some of my collaborators here. So a lot of this work that I showed you was done in collaboration with Hong Kong professor she G. And a lot of that work was done in Lawrence Livermore with Dr. Newman and Dr. Oakdale being collaborators there. Thank you. So we have time for questions. If anybody has a question oh, let's use the mike just so that everybody can hear you very much for the talk. Just regarding the comparison process, what characterization equipment do you recommend for getting the length scales of these structures? I'm sorry, what could you repeat? What characterization equipment do you use to look into the actual printed structures like a scanning electron microscope or we yes, sir. Depends on what property are looking far if you're looking for geometry than we are when typically use scanning electron microscope to look at the external geometry. We have also used X-ray, CT computed tomography to look into internal details on half a micron length scale. So if you'll make ten micron features, do those exist or have the shifter? Now if you're looking for other material properties like composition, you would use a different characterization technique, XPS or EPS to look at what chemicals are left behind after pyrolysis. Afm, not so much for the 3D, but particularly when you're looking at single voxels, to look at the profiles, heights of the voxels themselves. Other questions, Chris? Well, a general question. So you have the two Lai De saws. Were is that a true one light source? I'll do manipulate this so you spread it out. I'll do created that the beds to beam. Yes. So the two beam is searching for the right word. There are a few papers out there that incorrectly said you need to beams for two-photon lithography. You can do to four now lithography with a single beam of light. The reason it's called two-photon lithography is because within that same beam of light, two photons are simultaneously absorb. So if you look at the implementation of the system nano scribe, it has a single beam of light that's focused into a light spot and then moved around. We are not moving to beams and intersecting them. Well, for the poker is, how do you get the focus to you? What methods are you using? Yeah, so for focusing, we would use an objective lens, take a beam, let's say we have a Gaussian beam, focus our pass it through an objective lens which has a high numerical aperture, let's say 1.3 or 1.4. So that is going to be then focused into a diffraction limited spot. So that's part is going to be about 800 nanometers wide with numerical aperture 1.4 or so. So that 800 nanometer spot of light is sufficiently small to give me 150 nanometer features. Because only a section of that light's part is where most of the absorption is going to happen. And if I can make sure that I don't like the reactions proceed out too far off that region. I can have light spot, sorry, I can have printed parts that are 150 nanometer. So the key is to make sure you have asked smallest part as possible, which is with a high numerical aperture lens. And then with the resist that don't propagate very fast or don't react very fast out. So that's where traditional with our technique, you also need to make sure it's in the depth direction focused, and that's where the time-domain comes into play. Thanks. Thank you for a great talk. I appreciate that. My question is, what governs the degree of polymerization? Is it power exposure time, or what does it impact of temperature? If so? And my other question was, is it the acrylic based polymer you've been using? Or maybe you don't need to say if it's proprietary, but then I just was interested to know that. And what impact it will have on the glass transition temperature of your ball. And I guess Yeah, Let me answer. Let me answer one by one. We've answered some of these in the past, so let's pick what the material is. The material is accurate, actually a base, so the functional groups are accurate. Accolades polyacrylate. So there are more than one functional group on the same molecule. In terms of their degree of conversion. The degree of conversion depends on how many molecules have crosslinked and how many molecules crosslink, depending on the dosage, which is effectively a function of the density of light. And how long have you expose that to light. So the time of exposure and density of exposure, in our case, it also depends on how take each lights part IS, which is what, what's really being projector? Because it's not just a single spark, an entire image as being projector. So it depends on all these three things. In terms of the reaction or dependence on the rate of reaction depends on temperature. It is temperature dependent on which means that if you heat up this prop or heat up the resist as you are printing, you will see different sizes and different degrees of conversion. Now during this process, if it's harold an Ambien, the reaction itself in that small region generates enough heat to heat it up by a few degrees Celsius, not more. So assuming that it's constant temperature process is a good enough approximation for many of these reactions. In terms of the glass transition temperature, the more there is crosslinking, trying to figure out so it shifts the glass transition temperature. The more it's cross-linked, the more, I believe glossy it becomes. Primarily the temperature you work on deals with the glass transition temperature. Because at glass transition temperature these polymers start flowing and so that might impact the rigidity of the structures you are creating. So one thing to keep in mind is this is not a thermal process. So the processor itself is curing, which means it starts with the liquid which has its own glass transition temperature and so on. And it gets converted into this cured epoxy light material, which will have its own glass transition temperature. What we have tried out is if we heat it up, do we see it softening? It does not soften, it will actually start burning. So that is one suggesting that, that glass transition temperature is not such a good metric for this kind of material to under standards flowability properties. Second is we have seen the glass transition temperature. If you can look at just changes in modulus as a metric for glass transition. If you look at that, then we have seen that it depends a lot more on processing conditions which has power and speed in the cereal. And that effectively changes the number of cross-links, which is really degree of conversion. And what we have seen is if you go very, very fast, you end up getting very viscous like material relative to if you go very slow and literate, cross-link a lot. I would impact the post-processing once you've printed out. If you want to do further process, then that will impact because if the if it's not rigid than the post-processing might be a challenge. Yeah, that's what I was doing that. So we looked into the mechanical properties board, the viscoelastic and just looking at the non strain or strain rate dependent properties. So these are reasonably Richard with the elastic modulus of about three gigapascal. So very much a boxy like our thermo sacked like. And they will hold there size over time. So they're not creeping so much as opposed to, let's say if you printed on some of these traditional 3D printers for use UV light to Kyoto material. I'm going to ask the last question. So obviously the parallel approach is great for speeding up the x y printing. Is there any need to increase speed and the z-axis? And how would you go about doing that? So you still have to build them. We earlier. So our work has been replicated very recently, I believe about a month ago there was published and we had this idea, we just did not implemented before them. The idea is so if you stop and move up, then you are waiting a lot of time and not printing. Why do you could do is you could rapidly move it up and then keep projecting. So that takes a dart increases by about a factor of up to 75 to a 100 times in the z direction. So I can keep projecting and moving at the same time. So it's a more of a motion stage Bayes limitation and how do you project and move. So very similar to clip additive manufacturing, but with projection of these femtosecond light sheets. Alright, thanks professor. So how one more time?