Advances in holographic replication with the Aztec structure
Cowan, James
Holograms that are predominantly in use today as replicable devices for display, security, or packaging can generally be divided into two categories: either surface relief rainbow holograms, which include three dimensional images and intricate grating patterns, or reflection type volume holograms. The Aztec structure is a special surface relief device that combines aspects of both of these types. Its fabrication by holographic means requires techniques of both surface and volume holograms, and thus it is technically more difficult to make than either separately. The structure is deeper than the standard surface relief hologram, and its profile has the characteristic of several well defined steps, such that, when viewed on edge, resemble a stepped pyramid. Thus, replication of the Aztec structure requires special high resolution techniques to faithfully record the submicron features of the stepped profile, and thus is more difficult to manufacture. The visual characteristics of the Aztec structure are similar to the volume hologram, in that single colors, rather than rainbow colors, can be viewed. Also, a combination of single colors can be encoded into a single master, yielding unique visual effects.
 Good morning, ladies and gentlemen. I would like to talk to you about advances in holographic replication with the structure I've called Aztec. I realize some of you here have had some acquaintance with Aztec, but this talk is directed to those who have never ever heard of it. So what do we have out there today? Basically two types, surface relief structures that are replicated mechanically, volume reflective structures that are replicated optically. Let's look at the larger group, which as you already heard is a predominant method of replicating holograms. Surface relief structures can be divided into rainbow holograms to fraction grading structures. Rainbow holograms, rainbow colors, no single colors, three-dimensional horizontal parallax only viewable with lighting in one direction. And these we know from these the familiar Visa Dove and the Mastercard Globe. Fraction grading patterns, also rainbow colors, no single colors, mostly 2D, also 2D and 3D. Very complex patterns viewable from many angles. And here are some examples taken from a recent book called Optical Document Security. How are the surface relief structures made? Well, I think we're all pretty much familiar with the general process, but let's just review it. The alfaxus lithupecnix configuration, reference and object light are on the same side of the recording surface. Made like this, object reference, interference fringes perpendicular to the surface. The recording medium is photo resist. So when the development takes place, you're left with a surface that looks like a sine wave. And to replicate it, you form a nickel master from the photo resist. From the nickel, you can press the pattern into plastic. And then the plastic is metallized. And that's what we normally see as an embossed hologram. What about volume structures? Behavior is totally different. Full parallax with a single color uses a denisee configuration. Object and reference beams are on the opposite sides. It's optical instead of mechanical replication. So here's how they're made. Reference and object on opposite sides. Interference fringes parallel to the surface. And reconstruction. Reference light reflects off of the semi-transparent layers, usually photographic emulsion, documented gelatin or photopolymer. You get coherent reconstruction. No surface relief here whatsoever. The only way this can be replicated is optically. And generally, it's like you have photopolymer reeled off across a cylinder, which has a master hologram on it. And you actually make holograms on the production line. This is a process that is inherently more expensive than embossing. And here's an example of what you see. Full parallax, single color. And we're looking above and below and to the right and to the left of this particular image. How do we improve upon conventional holograms? We also, we have a very strong hint in nature's surface relief volume reflection hologram, the Morpho butterfly. Here's the Morpho retinor. Beautiful blue iridescent color. There is no color pigment in this wing. Here's another species, the Morpho absoloni. A slightly different color. Also, no color pigment here. How does that color arise? Here, by the way, is just a display case of Morphos. It's ubiquitous in the Caribbean. This is from the Caribbean island of Aruba. We did micrographs of the wing structure. And as you can see, at low magnification, it looks like a linear grading. But as the magnification increases, you see there's a complexity to the wing structure. And if we look more closely at the wing structure, we can see that it has this Christmas tree-like structure with little parallel veins extending out on either side. These veins are spaced a halfway-length apart for the light that is seen in reflection. And white light comes in from the top surface. White light comes in here, reflects off of each of these veins coherently, and all the other colors are absorbed. Can this be duplicated in photoresist? Well, the answer is yes, with the following modifications. Replace the undercut structure with a step structure. Achieve brightness by coating the step structure with a highly-reflecting metal like aluminum. How do we make it? We combine the off-axis and volume-recording geometries. By the way, the name Aztec is an acronym for diazo-footer-resist technology. But it also refers to the final structure that we get when we do this recording. And the way we make it is to combine the two methods that we just saw. We make in the same photoresist medium the volume-grading, which gives parallel fringes. And we have the so-called opening-grading. I'll describe that term later, which is off-axis grading, which gives fringes that are perpendicular to the surface. So we get two sets of interference fringes perpendicular to each other. Sorry. I seem to be missing a slide. Well, I'm sorry. So the opening structure opens up the surface to developer edgint. And one way of doing this is with three coherent aims, producing a honeycomb structure. And then if we put the steps into the structure, we get what I'm calling a single-color photonic crystal. We get single colors in the zero order, and we get diffractive colors dispersed off at angles away from the normal. If we record in narrow millimeter, centimeter-wide strips with slightly different step heights, we get what I call a color stripe grading. And here's a spectral scan of several of those stripes. It's also possible to not only use three beams to record the opening-grading, but to use five beams. And we get a structure kind of like this. And if we magnify it at normal incidence, we see many parallel planes. And looking at it at 60 degrees, we see very well-defined terraces. And again, many well-defined terraces here as well. And we can also use seven beams. Incidentally, the use of even beams leads to objectionable moray patterns. The contrast ratio from the high to the low exposure area is proportional to the square of the number of beams. So in this case, 49 to 1. In the previous case, 25 to 1 with three beams, it's 9 to 1. And here's the one with seven beams. We can also have a cell with polydispersed liquid crystal introduced. And we can change the voltage with a polydispersed liquid crystal. The index of refraction changes linearly. And therefore, the color that's seen in reflection is changed. And we can also isolate certain regions of the top surface to be tuned to red, blue, or green. What about the Aztec hologram? In this case, we may find that the off-axis color spectra is objectionable. So we want to reduce that. So we have an object beam and two reference beams. One reference is on the same side. The second reference is on the opposite side. So with a diffraction efficiency, then the off-axis minimizes and the volume maximizes like shown here. The surface diffraction efficiency varies as a Bessel function. The volume efficiency varies as a hyperbolic function. But the steps have to be extremely well defined in order for that efficiency to be high. If the steps are only moderately defined, it drops. The steps are barely defined. It drops even more. When we make the hologram, we do it as a so-called symmetric construction where the interference fringe curves are actually curved. And the development leads to slight curves in the structure. But the structure still shows the characteristic steps. And here are some single color images made with varying step heights. The blue image of the step height of 121 nanometers. The image on the right with a wavelength of 600 nanometers in the step height of 182 nanometers. And generally speaking, the steps here are about anywhere from five to ten steps. So this is at least an order of magnitude larger than your typical embossed hologram. We can also make an asymmetric profile where the so-called opening fringes that come in at a very large angle. And we're left with an asymmetric configuration which actually leads to very high efficiencies. Here's a typical set of efficiency curves for a five-level structure. By tilting this from a plus one to minus one, we can actually get different colors as shown here. We can also, if we go as much as ten levels, we get an envelope with many different merit curves underneath. If many narrow residences are closely spaced and wavelength, a single level plays, forms an envelope, and the result is a kind of a rainbow full parallax hologram. And this curve is based on scalar theory, but for an overall pitch of, in this case, three microns, it follows the full vector theory very closely. And here is an example of a blazed hologram embossed into plastic seen from the top. We can even see there's a degree of undercutting here. And here's a side view. And again, I'm saying that your typical embossed hologram has a depth about equal to one of these steps. So you can see we've got anywhere from 10 to 14 steps here. The reason this looks somewhat random is because this is a diffuse image, and the overall pattern would have a random pattern for diffuse images. But because the steps are very well defined, the color is quite uniform. And this is the object from which those micrographs were made. And here we're looking above and below and to the right and to the left. So there is full parallax. The full parallax is maintained. The color, the single color is maintained. And these little circles here, these little circles and this cross are focused in the plane, but this larger cross in the background is a full two inches behind the surface. And we see that's still sharp focus and this is rather extraordinary, I think, for an embossed hologram. It's also possible to replace the aluminum with other materials, other dielectric materials of high index that are actually transparent in the visible. For example, titanium dioxide and zinc sulfide at very high indices of refraction and actually form a very visible image, but they are transparent. So as a hologram replica device, the Aztec structure first allows for full parallax single colors that can be mechanically replicated. Second, it allows for easily viewed and simpler images in full color. And third, it's more difficult to replicate because of the complexity of the profile. And finally, challenge for the future. We should be able to find some way of embossing undercut structures. In that case, there would be no metal or dielectric coating required. The holographic method is ideal for recording undercut structures. The real challenge would lie in somehow finding a way to replicate that. And I know from experience that trying to replicate undercut structures is extremely difficult, but if we had, and I'm assuming we have great advances in embossing materials, we had some embossing materials with high elasticity, a lot of nice features, but if we could do that, then we could indeed replicate the butterfly, the original butterfly structure, and we wouldn't need these metal coatings. So, so far we're doing okay with the metal coating as is. It's very similar to standard embossed holography. The main difference is it's a deeper structure. That's it. Thank you. Thank you, James. In this short time to bring so much information, and I have to thank you in first another question. Have you ever tried tried metalizing an actual morpho butterfly wing and trying embossing that? That's an interesting thought, Jeff, but the actual morpho butterfly wing is extremely fragile. If you just touch it, it just rubs off. You really can't even touch it. It's extremely fragile, yes. Is it known how the butterfly grows its wings? I mean, the biological process is known or not yet? Well, I've had some people ask me, why has it taken you so long to develop this? And I said, well, think how long it took God to evolve this magnificent structure. I'm assuming a couple of million years. Yeah. Have you ever looked into the rubber inner masters? There's a bunch of literature about these sort of rubber soft inner masters to create from the photo resist, and I wonder if you've ever looked into any of that. I've looked at many, many, many, maybe some of the later ones I haven't seen, but certainly that's anything like that. I'll be very happy to look at. Thank you very much. And again, I think that it's still a very hopeful technology.
 Good morning, ladies and gentlemen.  I would like to talk to you about advances in holographic replication with the structure I've called Aztec.  I realize some of you here have had some acquaintance with Aztec, but this talk is directed to those who have never ever heard of it.  So what do we have out there today?  Basically two types, surface relief structures that are replicated mechanically, volume reflective structures that are replicated optically.  Let's look at the larger group, which as you already heard is a predominant method of replicating holograms.  Surface relief structures can be divided into rainbow holograms to fraction grading structures.  Rainbow holograms, rainbow colors, no single colors,  three-dimensional horizontal parallax only viewable with lighting in one direction.  And these we know from these the familiar Visa Dove and the Mastercard Globe.  Fraction grading patterns, also rainbow colors, no single colors, mostly 2D, also 2D and 3D.  Very complex patterns viewable from many angles.  And here are some examples taken from a recent book called Optical Document Security.  How are the surface relief structures made?  Well, I think we're all pretty much familiar with the general process, but let's just review it.  The alfaxus lithupecnix configuration, reference and object light are on the same side of the recording surface.  Made like this, object reference, interference fringes perpendicular to the surface.  The recording medium is photo resist.  So when the development takes place, you're left with a surface that looks like a sine wave.  And to replicate it, you form a nickel master from the photo resist.  From the nickel, you can press the pattern into plastic.  And then the plastic is metallized.  And that's what we normally see as an embossed hologram.  What about volume structures?  Behavior is totally different.  Full parallax with a single color uses a denisee configuration.  Object and reference beams are on the opposite sides.  It's optical instead of mechanical replication.  So here's how they're made.  Reference and object on opposite sides.  Interference fringes parallel to the surface.  And reconstruction.  Reference light reflects off of the semi-transparent layers,  usually photographic emulsion, documented gelatin or photopolymer.  You get coherent reconstruction.  No surface relief here whatsoever.  The only way this can be replicated is optically.  And generally, it's like you have photopolymer reeled off across a cylinder,  which has a master hologram on it.  And you actually make holograms on the production line.  This is a process that is inherently more expensive than embossing.  And here's an example of what you see.  Full parallax, single color.  And we're looking above and below and to the right and to the left of this particular image.  How do we improve upon conventional holograms?  We also, we have a very strong hint in nature's surface relief volume reflection  hologram, the Morpho butterfly.  Here's the Morpho retinor.  Beautiful blue iridescent color.  There is no color pigment in this wing.  Here's another species, the Morpho absoloni.  A slightly different color.  Also, no color pigment here.  How does that color arise?  Here, by the way, is just a display case of Morphos.  It's ubiquitous in the Caribbean.  This is from the Caribbean island of Aruba.  We did micrographs of the wing structure.  And as you can see, at low magnification, it looks like a linear grading.  But as the magnification increases, you see there's a complexity to the wing structure.  And if we look more closely at the wing structure, we can see that it has  this Christmas tree-like structure with little parallel veins extending out on either side.  These veins are spaced a halfway-length apart for the light that is seen in reflection.  And white light comes in from the top surface.  White light comes in here, reflects off of each of these veins coherently,  and all the other colors are absorbed.  Can this be duplicated in photoresist?  Well, the answer is yes, with the following modifications.  Replace the undercut structure with a step structure.  Achieve brightness by coating the step structure with a highly-reflecting metal like aluminum.  How do we make it?  We combine the off-axis and volume-recording geometries.  By the way, the name Aztec is an acronym for diazo-footer-resist technology.  But it also refers to the final structure that we get when we do this recording.  And the way we make it is to combine the two methods that we just saw.  We make in the same photoresist medium the volume-grading, which gives parallel fringes.  And we have the so-called opening-grading.  I'll describe that term later, which is off-axis grading,  which gives fringes that are perpendicular to the surface.  So we get two sets of interference fringes perpendicular to each other.  Sorry.  I seem to be missing a slide.  Well, I'm sorry.  So the opening structure opens up the surface to developer edgint.  And one way of doing this is with three coherent aims,  producing a honeycomb structure.  And then if we put the steps into the structure,  we get what I'm calling a single-color photonic crystal.  We get single colors in the zero order,  and we get diffractive colors dispersed off at angles away from the normal.  If we record in narrow millimeter, centimeter-wide strips  with slightly different step heights, we get what I call a color stripe grading.  And here's a spectral scan of several of those stripes.  It's also possible to not only use three beams to record the opening-grading,  but to use five beams.  And we get a structure kind of like this.  And if we magnify it at normal incidence, we see many parallel planes.  And looking at it at 60 degrees, we see very well-defined terraces.  And again, many well-defined terraces here as well.  And we can also use seven beams.  Incidentally, the use of even beams leads to objectionable moray patterns.  The contrast ratio from the high to the low exposure area  is proportional to the square of the number of beams.  So in this case, 49 to 1.  In the previous case, 25 to 1 with three beams, it's 9 to 1.  And here's the one with seven beams.  We can also have a cell with polydispersed liquid crystal introduced.  And we can change the voltage with a polydispersed liquid crystal.  The index of refraction changes linearly.  And therefore, the color that's seen in reflection is changed.  And we can also isolate certain regions of the top surface  to be tuned to red, blue, or green.  What about the Aztec hologram?  In this case, we may find that the off-axis color spectra is objectionable.  So we want to reduce that.  So we have an object beam and two reference beams.  One reference is on the same side.  The second reference is on the opposite side.  So with a diffraction efficiency, then the off-axis  minimizes and the volume maximizes like shown here.  The surface diffraction efficiency varies as a Bessel function.  The volume efficiency varies as a hyperbolic function.  But the steps have to be extremely well defined in order for that efficiency to be high.  If the steps are only moderately defined, it drops.  The steps are barely defined.  It drops even more.  When we make the hologram, we do it as a so-called  symmetric construction where the interference fringe curves are actually curved.  And the development leads to slight curves in the structure.  But the structure still shows the characteristic steps.  And here are some single color images made with varying step heights.  The blue image of the step height of 121 nanometers.  The image on the right with a wavelength of 600 nanometers in the step height of 182 nanometers.  And generally speaking, the steps here are about anywhere from five to ten steps.  So this is at least an order of magnitude larger than your typical embossed hologram.  We can also make an asymmetric profile where the so-called opening fringes that come in at a very large angle.  And we're left with an asymmetric configuration which actually leads to very high efficiencies.  Here's a typical set of efficiency curves for a five-level structure.  By tilting this from a plus one to minus one, we can actually get different colors as shown here.  We can also, if we go as much as ten levels, we get an envelope with many different merit curves  underneath. If many narrow residences are closely spaced and wavelength, a single level plays,  forms an envelope, and the result is a kind of a rainbow full parallax hologram.  And this curve is based on scalar theory, but for an overall pitch of, in this case,  three microns, it follows the full vector theory very closely. And here is an example of a blazed  hologram embossed into plastic seen from the top. We can even see there's a degree of undercutting here.  And here's a side view. And again, I'm saying that your typical embossed hologram has a depth  about equal to one of these steps. So you can see we've got anywhere from 10 to 14 steps here.  The reason this looks somewhat random is because this is a diffuse image, and the overall pattern  would have a random pattern for diffuse images. But because the steps are very well defined,  the color is quite uniform. And this is the object from which those micrographs were made.  And here we're looking above and below and to the right and to the left. So there is full parallax.  The full parallax is maintained. The color, the single color is maintained. And these little  circles here, these little circles and this cross are focused in the plane, but this larger cross  in the background is a full two inches behind the surface. And we see that's still sharp focus  and this is rather extraordinary, I think, for an embossed hologram. It's also possible to  replace the aluminum with other materials, other dielectric materials of high index that are actually  transparent in the visible. For example, titanium dioxide and zinc sulfide at very high indices  of refraction and actually form a very visible image, but they are transparent. So as a hologram  replica device, the Aztec structure first allows for full parallax single colors that can be  mechanically replicated. Second, it allows for easily viewed and simpler images in full color.  And third, it's more difficult to replicate because of the complexity of the profile.  And finally, challenge for the future. We should be able to find some way of embossing  undercut structures. In that case, there would be no metal or dielectric coating required.  The holographic method is ideal for recording undercut structures. The real challenge would lie  in somehow finding a way to replicate that. And I know from experience that trying to replicate  undercut structures is extremely difficult, but if we had, and I'm assuming we have great advances  in embossing materials, we had some embossing materials with high elasticity, a lot of nice  features, but if we could do that, then we could indeed replicate the butterfly, the original  butterfly structure, and we wouldn't need these metal coatings. So, so far we're doing okay with  the metal coating as is. It's very similar to standard embossed holography. The main difference  is it's a deeper structure. That's it. Thank you. Thank you, James. In this short time to bring so  much information, and I have to thank you in first another question. Have you ever tried  tried metalizing an actual morpho butterfly wing and trying embossing that?  That's an interesting thought, Jeff, but the actual morpho butterfly wing is extremely fragile.  If you just touch it, it just rubs off. You really can't even touch it. It's extremely fragile, yes.  Is it known how the butterfly grows its wings? I mean, the biological process is known or not yet?  Well, I've had some people ask me, why has it taken you so long to develop this? And I said,  well, think how long it took God to evolve this magnificent structure. I'm assuming a couple of  million years. Yeah. Have you ever looked into the rubber inner masters? There's a bunch of literature  about these sort of rubber soft inner masters to create from the photo resist, and I wonder if you've  ever looked into any of that. I've looked at many, many, many, maybe some of the later ones I haven't  seen, but certainly that's anything like that. I'll be very happy to look at.  Thank you very much. And again, I think that it's still a very hopeful technology.
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Good morning, ladies and gentlemen. I would like to talk to you about advances in holographic replication with the structure I've called Aztec. I realize some of you here have had some acquaintance with Aztec, but this talk is directed to those who have never ever heard of it. So what do we have out there today? Basically two types, surface relief structures that are replicated mechanically, volume reflective structures that are replicated optically. Let's look at the larger group, which as you already heard is a predominant method of replicating holograms. Surface relief structures can be divided into rainbow holograms to fraction grading structures. Rainbow holograms, rainbow colors, no single colors, three-dimensional horizontal parallax only viewable with lighting in one direction. And these we know from these the familiar Visa Dove and the Mastercard Globe. Fraction grading patterns, also rainbow colors, no single colors, mostly 2D, also 2D and 3D. Very complex patterns viewable from many angles. And here are some examples taken from a recent book called Optical Document Security. How are the surface relief structures made? Well, I think we're all pretty much familiar with the general process, but let's just review it. The alfaxus lithupecnix configuration, reference and object light are on the same side of the recording surface. Made like this, object reference, interference fringes perpendicular to the surface. The recording medium is photo resist. So when the development takes place, you're left with a surface that looks like a sine wave. And to replicate it, you form a nickel master from the photo resist. From the nickel, you can press the pattern into plastic. And then the plastic is metallized. And that's what we normally see as an embossed hologram. What about volume structures? Behavior is totally different. Full parallax with a single color uses a denisee configuration. Object and reference beams are on the opposite sides. It's optical instead of mechanical replication. So here's how they're made. Reference and object on opposite sides. Interference fringes parallel to the surface. And reconstruction. Reference light reflects off of the semi-transparent layers, usually photographic emulsion, documented gelatin or photopolymer. You get coherent reconstruction. No surface relief here whatsoever. The only way this can be replicated is optically. And generally, it's like you have photopolymer reeled off across a cylinder, which has a master hologram on it. And you actually make holograms on the production line. This is a process that is inherently more expensive than embossing. And here's an example of what you see. Full parallax, single color. And we're looking above and below and to the right and to the left of this particular image. How do we improve upon conventional holograms? We also, we have a very strong hint in nature's surface relief volume reflection hologram, the Morpho butterfly. Here's the Morpho retinor. Beautiful blue iridescent color. There is no color pigment in this wing. Here's another species, the Morpho absoloni. A slightly different color. Also, no color pigment here. How does that color arise? Here, by the way, is just a display case of Morphos. It's ubiquitous in the Caribbean. This is from the Caribbean island of Aruba. We did micrographs of the wing structure. And as you can see, at low magnification, it looks like a linear grading. But as the magnification increases, you see there's a complexity to the wing structure. And if we look more closely at the wing structure, we can see that it has this Christmas tree-like structure with little parallel veins extending out on either side. These veins are spaced a halfway-length apart for the light that is seen in reflection. And white light comes in from the top surface. White light comes in here, reflects off of each of these veins coherently, and all the other colors are absorbed. Can this be duplicated in photoresist? Well, the answer is yes, with the following modifications. Replace the undercut structure with a step structure. Achieve brightness by coating the step structure with a highly-reflecting metal like aluminum. How do we make it? We combine the off-axis and volume-recording geometries. By the way, the name Aztec is an acronym for diazo-footer-resist technology. But it also refers to the final structure that we get when we do this recording. And the way we make it is to combine the two methods that we just saw. We make in the same photoresist medium the volume-grading, which gives parallel fringes. And we have the so-called opening-grading. I'll describe that term later, which is off-axis grading, which gives fringes that are perpendicular to the surface. So we get two sets of interference fringes perpendicular to each other. Sorry. I seem to be missing a slide. Well, I'm sorry. So the opening structure opens up the surface to developer edgint. And one way of doing this is with three coherent aims, producing a honeycomb structure. And then if we put the steps into the structure, we get what I'm calling a single-color photonic crystal. We get single colors in the zero order, and we get diffractive colors dispersed off at angles away from the normal. If we record in narrow millimeter, centimeter-wide strips with slightly different step heights, we get what I call a color stripe grading. And here's a spectral scan of several of those stripes. It's also possible to not only use three beams to record the opening-grading, but to use five beams. And we get a structure kind of like this. And if we magnify it at normal incidence, we see many parallel planes. And looking at it at 60 degrees, we see very well-defined terraces. And again, many well-defined terraces here as well. And we can also use seven beams. Incidentally, the use of even beams leads to objectionable moray patterns. The contrast ratio from the high to the low exposure area is proportional to the square of the number of beams. So in this case, 49 to 1. In the previous case, 25 to 1 with three beams, it's 9 to 1. And here's the one with seven beams. We can also have a cell with polydispersed liquid crystal introduced. And we can change the voltage with a polydispersed liquid crystal. The index of refraction changes linearly. And therefore, the color that's seen in reflection is changed. And we can also isolate certain regions of the top surface to be tuned to red, blue, or green. What about the Aztec hologram? In this case, we may find that the off-axis color spectra is objectionable. So we want to reduce that. So we have an object beam and two reference beams. One reference is on the same side. The second reference is on the opposite side. So with a diffraction efficiency, then the off-axis minimizes and the volume maximizes like shown here. The surface diffraction efficiency varies as a Bessel function. The volume efficiency varies as a hyperbolic function. But the steps have to be extremely well defined in order for that efficiency to be high. If the steps are only moderately defined, it drops. The steps are barely defined. It drops even more. When we make the hologram, we do it as a so-called symmetric construction where the interference fringe curves are actually curved. And the development leads to slight curves in the structure. But the structure still shows the characteristic steps. And here are some single color images made with varying step heights. The blue image of the step height of 121 nanometers. The image on the right with a wavelength of 600 nanometers in the step height of 182 nanometers. And generally speaking, the steps here are about anywhere from five to ten steps. So this is at least an order of magnitude larger than your typical embossed hologram. We can also make an asymmetric profile where the so-called opening fringes that come in at a very large angle. And we're left with an asymmetric configuration which actually leads to very high efficiencies. Here's a typical set of efficiency curves for a five-level structure. By tilting this from a plus one to minus one, we can actually get different colors as shown here. We can also, if we go as much as ten levels, we get an envelope with many different merit curves underneath. If many narrow residences are closely spaced and wavelength, a single level plays, forms an envelope, and the result is a kind of a rainbow full parallax hologram. And this curve is based on scalar theory, but for an overall pitch of, in this case, three microns, it follows the full vector theory very closely. And here is an example of a blazed hologram embossed into plastic seen from the top. We can even see there's a degree of undercutting here. And here's a side view. And again, I'm saying that your typical embossed hologram has a depth about equal to one of these steps. So you can see we've got anywhere from 10 to 14 steps here. The reason this looks somewhat random is because this is a diffuse image, and the overall pattern would have a random pattern for diffuse images. But because the steps are very well defined, the color is quite uniform. And this is the object from which those micrographs were made. And here we're looking above and below and to the right and to the left. So there is full parallax. The full parallax is maintained. The color, the single color is maintained. And these little circles here, these little circles and this cross are focused in the plane, but this larger cross in the background is a full two inches behind the surface. And we see that's still sharp focus and this is rather extraordinary, I think, for an embossed hologram. It's also possible to replace the aluminum with other materials, other dielectric materials of high index that are actually transparent in the visible. For example, titanium dioxide and zinc sulfide at very high indices of refraction and actually form a very visible image, but they are transparent. So as a hologram replica device, the Aztec structure first allows for full parallax single colors that can be mechanically replicated. Second, it allows for easily viewed and simpler images in full color. And third, it's more difficult to replicate because of the complexity of the profile. And finally, challenge for the future. We should be able to find some way of embossing undercut structures. In that case, there would be no metal or dielectric coating required. The holographic method is ideal for recording undercut structures. The real challenge would lie in somehow finding a way to replicate that. And I know from experience that trying to replicate undercut structures is extremely difficult, but if we had, and I'm assuming we have great advances in embossing materials, we had some embossing materials with high elasticity, a lot of nice features, but if we could do that, then we could indeed replicate the butterfly, the original butterfly structure, and we wouldn't need these metal coatings. So, so far we're doing okay with the metal coating as is. It's very similar to standard embossed holography. The main difference is it's a deeper structure. That's it. Thank you. Thank you, James. In this short time to bring so much information, and I have to thank you in first another question. Have you ever tried tried metalizing an actual morpho butterfly wing and trying embossing that? That's an interesting thought, Jeff, but the actual morpho butterfly wing is extremely fragile. If you just touch it, it just rubs off. You really can't even touch it. It's extremely fragile, yes. Is it known how the butterfly grows its wings? I mean, the biological process is known or not yet? Well, I've had some people ask me, why has it taken you so long to develop this? And I said, well, think how long it took God to evolve this magnificent structure. I'm assuming a couple of million years. Yeah. Have you ever looked into the rubber inner masters? There's a bunch of literature about these sort of rubber soft inner masters to create from the photo resist, and I wonder if you've ever looked into any of that. I've looked at many, many, many, maybe some of the later ones I haven't seen, but certainly that's anything like that. I'll be very happy to look at. Thank you very much. And again, I think that it's still a very hopeful technology.
two types, surface relief structures that are holograms. Surface relief structures can be divided into rainbow holograms to fraction colors, no single colors, three-dimensional cylinder, which has a master hologram on it. And relief volume reflection hologram, the Morpho Here, by the way, is just a display case of micrographs of the wing structure. And as you can And the way we make it is to combine the two of several of those stripes. It's also possible to not only use three beams to record the patterns. The contrast ratio from the high to the still shows the characteristic steps. And here the steps are very well defined, the color is hologram replica device, the Aztec structure for easily viewed and simpler images in full color. And third, it's more difficult to similar to standard embossed holography. The main