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Large format digital colour holograms

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Large format digital colour holograms
Produced using RGB pulsed laser technology
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Large format digital colour holograms produced using RGB pulsed laser technology
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RGB pulsed laser technology provides a natural way to circumvent the problems of vibration inherent in conventional CW holographic printer schemes. Using such technology we have been able to print 1-step dot-matrix digital holograms at speeds of up to 50 RGB colour pixels per second in relatively compact printer configurations. Typical hologram pixel sizes that have been employed are around 1 mm diameter. Both full parallax and single parallax digital reflection holograms have been generated in this way with sizes of up to 1 m × 1.5 m. RGB transmission rainbow holograms have also been generated using this approach. Quicker generation of digital holograms is possible using a variety of 2-step pulsed laser printer schemes, the simplest of which consists of the contact or close copying of an original master dot-matrix hologram that has been specially processed. Other 2-step techniques such as H1:H2 schemes have required more powerful RGB pulsed lasers and yet have shown that they are capable of producing one–off smaller format holograms at high speed.
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so thank you Hans they're inviting me to speak today I'd like to to discuss a little bit and tell you a little about the technology we've been developing jeweler for digital color holographic printing and particularly using pulsed lasers so the technology that we used to produce these types of display over here the so I'd like
to to talking to start with about what is 0 1 and 2 digital holographic printer why we use a pulsed lasers in the 1st place then the design of the type of printers that we and the XYZ using and the lasers that we use in them and then I'd like to talk a little bit about some improvements we made to the laser technology particularly with reference to short cavity pulsed lasers some then I'd like to also discussed a new type of printer that we testing at the moment which is based on the L cost display technology and then also would like to come to the cockpit the topic of copying holograms because obviously when you write a hologram pixel-by-pixel like we do over here even with a pulsed laser it takes a rather a long time and um probably won't have time to talk about the work we've done today also on high energy pulsed lasers usually you need a relatively small energies to produce these types of holograms because you the pixel size is small but for some applications and some schemes union higher energy lasers we have been working on that so this is a general scheme of the type of
holographic printer that we've been developing can be used to make what we call 1 step hologram which is I guess like this or it can also be used to make a variety of master holograms from which you then copy using a variety of schemes to produce a final holograph basically we have 3 pulsed lasers this more difficult looks like this mouse uh red pulsed-laser green pulsed-laser and blue pulsed-laser would basically splits each 1 of these beams using beam splitters into a reference being which then goes through some conditioning optics and is then brought to bear on holographic films and so also of course object beam which goes through games and conditioning and then if we use an LCD to imprint digital data on that object being a high numerical aperture objective to focus down to produce a little 1 millimeter by 1 millimeter pixel the same point where you have the impinging reference being and then that causes a greeting to form on the holographic film and of course then we have an advance the film advanced system which allows us to advance the film in 2 dimensions on and then of course we have exactly the same thing for the red and the green and blue and all the pixels and finally overlap so that's the basic scheme that we're talking about
we think about copying because you can make a master hologram all the final hologram like that we think about copying than we think that we make a master hologram would go to make a final copy from it so we have various types of copies we can make from this type of technology so on this diagram we have the green and turquoise places the master and then obviously the red is the and exposed film that you can make a copy on and you just use a context coupling scheme typically with a pulsed laser so typically the context the masters typically the master is a reflection hologram and you need a low-energy scanning a laser beam to do that on over here you can also make what we call a close copy so again you make a different type of master with additional data on a different digital data on it and you copy at a slight distance using usually an aperture and you can all but
you're probably know then the scheme of copying which is called h 1 h 2 where you make a master and then at a large distance which corresponds to the viewing distance of a hologram you make a copy and typically when you're talking about RGB holography you want a reflection master and you need a higher energy RGB laser which is 1 of the reasons we've been doing work also on high-energy RGB lasers so that's a typical
um photographic print this particular 1 is the 1 we use in Vilnius to print holograms and has been used to print that 1 it's made by XYZ imaging which is in Montreal Canada which is a company that we stand out to 4 5 years ago and I could just the sink so it's comprised of the main optical units where you have the pulsed laser and all the objects obviously the computer control underneath all the power supplies for the laser etc. and then on this side is the film advance unit where you have a film carriage which can move from left to right and the actual film is on role is in a vacuum tensioning system which brings it up and down that's another holographic printed that we produced enjoy a lot in
I think 2001 identical optical scheme as the previous 1 except really the only thing in which is different is that instead of a film advanced system we use a glass plate so typically this system could use a meter by meter glass plate and then you can write holograms onto glass coated materials so why
not use pulsed lasers and not users CW lasers well the the obvious reason is is freedom from vibration and particularly when you talk about the one-step printers or making a master when you print so fast speed using a pulsed laser maybe say 60 holographic pixels the 2nd even with a small pixel size like we have over here your you that you have to move the film fast and given the fact that you need a micron resolution to your interference pattern that you can work out that you need to have exposure times which render microsecond so is not very efficient to use a CW laser the best of times because obviously the energy would have to be be all the power would be very large and then you just shattering reverse small period of time and so you have the motion of the film which ultimately provides a constraint also the vibration if you think of copiers then it depends intrinsically perhaps you don't need to use pulsed lasers um it depends whether you overlap the pixels the area that you're copying so in the contact copy for example you can use the slit for a spot and sometimes the spots can be juxtaposed sometimes they can be overlapped if this strongly overlapped then you have the problem of the interference patterns adding up coherently or incoherently and generally you want to keep things stable whether or not you use a pulsed laser and then in this case so for the case of strongly overlapping pixels you pick pulsed-laser simply because they're useful devices which happen to have the correct wavelength the same way the things that you've made a master and if they're not so strongly overlap is in some coping schemes then the vibration obviously is a strong constraint and using a pulsed laser gets you over that particularly for the H 1 H 2 scheme where you've got the master and the copy of a very large distance from your potentially very sensitive to vibration and using a pulsed laser can be a great benefit I so the type
of printers we using at the moment of based on what we call long cavity of pulsed laser technology so this is an old photo of RGB pulsed-laser that we may probably in 2001 but the lasers which we using at the moment very similar repetition rate something like 30 hertz energies approximately 3 Mitchell's chills each Calif well colors of 448 532 660 nanometers and pulse lengths which typically 40 to 50 nanoseconds some this type of technology by itself has a less than ideal stability pulsed stability and you generally need to active stabilization of the cavity lengths to get sufficient stability so that you don't get horrible black pixels when you print some of these telegrams on the LCD technology that we use in the current printers is the standard twisted nematic LCDs 1 of the problems it has is limited to around 30 hertz repetition rate and then you have to heat to around 50 degrees centigrade to get that sort of repetition rates from it and these panels that we use a relatively inefficient like to
just talk a little bit more in detail of the current design that we use for a holographic printer and and basically to show how it can be used to make the different forms of holograms to be masterful the one-step hologram so when we designed this we call it a universal law dual-mode holographic printer because the same holographic printer could be switched to produce transmission holograms reflection holograms one-step holograms rainbow holograms h 1 h 2 etc cetera and in each case the digital data was transformed and the geometry of the recording was changed a little bit but just to go during really briefly on this diagram shows just the green channel let's say generally we stack the green the red and the blue 1 on top of the other and they have a pretty much identical optical schemes so here is the green pulsed-laser thing going through a splitter forming a reference beam of object being sorry and the reference beam the reference beam can be directed even as a beam which comes from the opposite side of the holographic film in which case you have reflection hologram or it can be directed around here to the same side of the holographic film in which case you have a transmission hologram in the object being comes down here into a telescope we use a lens array microlens array here which we specially designed to basically but it does a few things including choose the pixel size of the hologram and also to condition the microstructure of the individual holographic pixel and holographic films so 1 of my 1st where is it and this is the LCD so the basically the been comes through the lens of race and the access really rays from the misery will then be collimated by this eliminate an LCD which for certain types of holograms needs to be moved in the two-dimensional fashion in synchronization with the film for other types of Lagrange doesn't and then it goes downstream through polarizer into a high numerical aperture lens which we designed especially for each of the different colors then this film obviously I've said before any other diagram it's it's mate to move in a two-dimensional fashion it can also be moved with certain rollers so that the angle with respect to the axial raising in the object beam can be changed the going on this is
another view of it from the side so you can see clearly the LCD here uh polarizer going through the the heian a lens being focused down onto a pixel and here again in a detail where you see the lens focusing the race down and where we've put the film plane downstream of the Fourier plane so that the reference beam is actually not quite large and we would use this technique for example typically in creating a transmission master hologram where we would strongly overlap the pixels but this would be another
scheme for example when we have a reference beam from the opposite side of the film that we create a reflection hologram but again when the film is downstream and again we create the relatively strongly overlapped set of holographic pixels and this is this would be suitable from H 1 H 2 copies it which in reflection now if we were making an h 1 h 2 copy we could also change the density in the vertical and horizontal directions for example we can
also make transmission transmission masters using just 1 color and facts you don't need an RGB laser for this and you can make a rainbow holograms and you can film into an angle so you can get the chromatic angle alternatively you can use of ones that system so here this would be the scheme that we use for this hologram when you have the reference beam coming from the opposite side so it's a reflection holograms and sign this time the emulsion is just a little bit downstream of the 4 airplanes so you get a smaller pixel and you tend not to overlap the pixels simply because you want to use it as a one-step final holograms and so you don't want to diminish the diffraction efficiency by averaging the holograms so you were right plurality of pixels which are juxtaposed rather than overlap going on to the type of
places that we use you know if you can see the some of the figures are so small that this would be a modern laser that we'd use in the current printers it's basically a thing laser which is built out of 20 cavities 1 oscillates at 1 0 6 4 9 meters and we frequency double that 532 nanometers the other is a Yankee laser which is oscillating at 1 3 1 9 9 0 meters now the cross section for the 1 3 1 9 and then the meter line is rather smaller than the 1 0 6 4 but you can inhibit the 106 for quite easily from lasing and so you can then double and triple to produce 660 and 440 and this produces a nice scheme for producing an RGB laser generally we use a linear cavity for example here we have 2 and members and error an output cut and the crystal here these lands lamp-pumped generally found and we have several frequency-selective elements within the cavity to ensure that the temporal coherence is what you want and also the energy stability and of course that passively Q-switched so we use saturable absorbers and the 1 3 1 9 laser is very similar to the 1 6 4 laser so you can see that I can find my cursor again looking at the green laser the output comes out of the output coupler generally is then focus through the KTP crystal producing 532 and then the beam is collimated in the 1 3 1 9 nanometer laser we use a doubling and tripling crystal appropriate for those wavelengths and would produce red and blue get generally the quality of the beam really good because during the and linear conversion you focused on 2 very small size have natural diffractive cleaning looking at the sort of parameters that we can we get around formally chose you can see here's actually 1 laser that we made I just took was from our manual and we measured 4 . 8 6 in the rate 3 . 4 8 in the blue and 6 and the green you could see that without active stabilization the stability is not too good if you can look at the 3rd line down it's in some points the plus minus 10 % the which is not so great when you wanna write a
hologram like that so 1 of the things which is really important is to actively stabilise will actually passively or actively stabilise the laser cavity and then just here I draw a graph of energy versus time over 10 to 16 hour period will look at the output of the laser and when we apply stabilization you see you have very good signal which is quite appropriate for writing holograms a minute you stop stabilization you get mode of the type of places are characterized by motorists step frequency-selective elements in them and that the optical path length of the laser cavity can change so generally what we do is we um the several different techniques but in Jolo we tend to use a heated Reimerink whereby we have a cylindrical million to which we heat to very accurate fashion and we put an in mirror on the end of that says we he creates the cylinder the end there will move by some very small distance if we plot that a real merit temperature here which is equivalent to the cavity length versus the standard deviation and energy you see that you have this sort of natural shape you have 2 minima and you have some maximum and you really want like to sit in this minimum region you can also plot the energy versus the the cavity length and you can see that it's the inverse of so you can actually look at the energy of this laser and it tells you where it wants to be in what it's doing and so you can of course make and mathematical algorithm with a computer to change the temperature of the Romero and then track and so for example you see over this period here where we stabilized it generally the temperature is being changed like this the so this was probably no need to
show you some examples of the celebrated because you've seen plenty today and in the coffee room but of course JOA and XYZ have done quite a few were campaigns with advertising agencies and stuff using this technology of 1 step printing generally you can get very high relatively high quality results so that's where we are
today the printing at 30 hertz so hologram like this takes about 6 hours to print generally if you use a work 28 millimeter uh what 1 . 6 mm pixel and around 24 hours if you use a . 8 mm pixel and what is we want to improve that also the current technology today is rather as I said it's a little bit unstable and you need to actively stabilise the lasers in order to make them behave well if you make too much noise around your printer it will miss this source so it would be nice to stabilize it to improve the laser technology 1 of the ideas we had with this which we feel is a very promising and were starting to do work on it is generally reducing the size of the laser so long cavity lasers basically have cavity length so big what we do what we started to do now is to make them around this large and this is a commercial laser which we made we make a nite included some just for reference referring to show you the size of of the disk laser is approximately the same size as our RGB lasers it's random meter long the resonators themselves are around me too long so the resonator both resonators would sit in like this and still out pretty much the whole of the laser and other nonlinear conversion optics would sit in the middle we've now gone down to a laser which is this size around 120 millimetres long and that then produces the 106 for nanomedicine 1 3 1 9 centimeters because you need to to those of the latest but that's a detail showing you the actual pump chamber for the land and if I remove on this during the pump chamber you see just the 65 mm Crystal of Newtonian now here and you see the sort of scheme that we use in which is very much identical to the long cavity laser itself output capital which also happens to be an um if you have a high reflection Romero polarizer you switch and and summer waveplates to stop spatial hole-burning since it's a linear cavity so very similar to the design of the lung cavity lasers using very similar crystals and
stuff of course it produces less energy this is a little scheme shown you how we do the nonlinear conversion gain it's identical crystal KTP with various telescopes and you get 532 nanometers and generally we can get 400 micro jewels pulse in and in comparison to the old technology long cavity lasers of 3 Mitchell said about it's easy to get this thing to work at 60 hertz it's easy to get it to work at higher because you could go to maybe 120 hertz with this land to technology without too much problem because it's smaller it's much more rigid and so generally the optical path length stays much better fixed so yeah has a thermal lands that the old lasers you have to optimize the laser for particular frequency of repetition of these you can just you know it's easy because the geometry is is less stringent because it's smaller and more generally the kind of stability is that we can get is from millions of pulses we can get better than plus or minus 3 per cent
that the typical realization of the blue or the red channel so you could produce exactly the same way red typically we can get 450 Mike rituals but also we've demonstrated this up to 60 hertz same same
stability and you can also make a red and the blue whereby you get the red and the blue from the single 1 3 1 9 or you make just below so typically if you run it in just the blue mode where you try to get all of your 1 3 1 9 to be converted to 440 then you can get around 250 rituals pulse so the type of
stabilization systems we use for the short cavity lasers are a little different from the long cavity lasers and this is illustrated by this graph here again this is the temperature of the rear mirror amount and as we scanned the temperature of the real mayor amount we can plot the standard deviation of the output energy and you see you have various stable operation followed by very abrupt onset of unstable operations and it's more difficult to actively stabilise laser like this because in fact the laser just doesn't tell you what it's doing it's working fine and then if the laser drifts into an unstable reason it will simply from the 1st pulse start behaving badly to generate how we stabilise these lasers is we surround them by a metal surface on which we completely control the temperature uh and then assuming you don't have any heat sources within the volume you know that the temperature at any point within that synthesis is constant so we can maintain the volume temperature very accurately then if before we write a hologram we make a scan as we show in this graph you can simply position the laser In say for example this position here and it will sit there for hours and hours and hours and hours and tens of millions of pulses the like
this for example where you could see a lot of pulses over 15 hours and there's not 1 single policy which is outside the limited class of minus 4 % pp
it's worth saying just a little bit about some of of the performance of these lasers because generally the smaller you make the laser but shorter the shorter the policy you would expect to come out of it and the silver halide emulsions are generally much more sensitive to pulse lengths over 30 nanoseconds you go on the 30 nanoseconds depending on wavelength and then the diffraction efficiency that you can get tends to drop so it's a great concern to try and get something like 40 50 nanoseconds out of these laser systems and the 1st warriors squashing the whole thing down would just get you into the 10 nanosecond regimes that wouldn't be very useful however we see that what you can do is you can change the output coupler the reflectivity which is more or less useful but more importantly you can actually change the initial transmission of the saturable absorbers within the cavity and so for example looking at this graph here we go from 30 nanoseconds add up to over 150 nanoseconds so as we change the initial transmission of saturable absorber of course
as you change the initial transmission of the sexual absorber and you get a longer pulse you pay a price for that and that's the energy goes down so for example if you look at this graph over here we can start off with around 8 many jewels this is the 1 6 4 9 meters for a 20 % initial transmission and then as we go up to the 80 % region which would give us near 100 nanoseconds output pulse then we're going down to around 1 minute the nevertheless
you don't need much energy for holograms like this so 1 minute show it's not such a problem you can actually go further than this and you can say well why why do we want to use lamps in the 1st place why not go to diet pumping and I guess the answer to that is that if you need more energy than lamps relatively inexpensive and is there a good way to get more energy if you need less energy and so on and you need higher repetition rates than dyads articulate a good solution over 200 hertz perhaps you'd say you wanna go to our diets so with that in mind we've been developing a diet systems based on exactly the same architecture here for example is a laser that we're working on at the moment typical cavity length is around 90 mm and so it's small thing around this big pump with a CW laser diode is of the collimation optics the dilute radiation would come through a fiber-optic which flux in just here and this is
a better view of the whole thing you can see here the 8 0 8 cm died radiation would come in and would be focused into the newtonian YAG crystal which could also be for example vanadate as well some and you have very it's a very similar layout you have a real hard this time coated in a slightly different way to transmit data related reflect the same 1 3 1 9 and output coupler polarizer exactly the same stuff and generally you you can get round about 100 might rituals of 1 3 1 9 0 that 50 nanosecond pulses in the kilohertz regime so those are the sort of innovations in the laser
parts of the technology that we're trying to make the moment but it's also very important to pair this up with the new panel technology which is available as you all know L cost displays now I really providing resolution in In displays they have better performance than their LCD cousins you can get around 71 % efficiency reflective efficiency in you would it they can work at much higher repetition rates as I said before the LCD panels work up to 30 hertz not printers if you really try hard and you heat them with these panels you can go up to 60 hertz and probably 120 and even more probably with the latest panties panels from Sony up to 2 100 hertz so that really helps you a lot in writing a hologram like this if you can keep the if you can make the writing times smaller also it's interesting because the efficiency of these panels is better contrast ratio better you get better holograms and you need less energy and that fits in very nicely with using short cavity lasers and some places so we have a demonstration system which working on at the moment which is an actually printer which is working at 60 holographic pixels per 2nd and potentially we wish to upgrade this 200 and 20 pixels it's based on the display from Britain and brilliant called the B R 7 6 8 h c and you can see the type of panels that you have there the type of printer that we now have to design is a little bit different and its work just going through but the sort of changes you have a this is a game for 1 colour channel you have a green laser here so ought could be readily on and it's that's it into through beamsplitter into a reference beam which goes around here and it's puts it into an object beam which goes around here this world is just to make the reference path length equal to the object path length and then it goes into the standard lens arrays system that we talked about before but then you have to change a little bit because you need to make very specialized for specialized optical system In order to use these reflective panels generally you need to initiate a focal telecentric reversing system using a McNeil polarizer with the course displays coupled with the the high numerical aperture objective to do that that's just
the details of that system there and that's the ray trace of a showing the material polarizer where your light comes in and is going to the L. C. L. cost display being reflected back and then is being brought to be high in a lens and then made into a pixel at this point here the of that's another
detail of the type of objects that we're using but
then going back to copies because of copying and is very important because even if you write these holograms very quickly then not quick enough position before this hologram takes around 6 hours to make we get to 60 hertz will take 3 hours to make 120 1 and a half hours is still a long time on the printers of course quite expensive so it's generally when you go to advertising clients they want to have hundreds thousands of these holograms and very quickly so how do you do that is useful to make master holograms quickly using this technology and the printers will be smaller and cheaper but you still have a problem you can't get those speeds you can't make something work probably at 10 kilohertz with this technology and or at least I can't see how to do it so it's important to talk about copies so I bring up the slide that I had before which is the types of copy that you can use the contact copy the close copy for the H 1 H 2
copies we've been working on both the contact copy and also the h 1 h 2 copies each 1 H 2 got of course needs a lot more energy and generally panchromatic materials not so sensitive as the old monochromatic material so you need jewels of energy and so we haven't fully explored that yet and we haven't got jewels in the red and the blue has yet although we have hundreds of many jails so up present target for copying is more the content copier and I just like to
say a few words on the type of experiments we've been doing with the contact copying this is a schematic version of common contact Copia using a long cavity RGB laser so the laser typically In this box here with optics and then we put our film to be copied in this book and do we can
use this little we can use a spot method and this is this particular set of diagrams shows a spot scanning methods we have investigated from probably
see here better white laser beam coming out of the box and then heating a sandwich which is composed of a master hologram should basically tuned version of that hologram so that you don't have any collapse of the emulsion replays exactly the right laser wavelengths and so and then you basically but the unexposed hologram of plate on top of it film on top of it and then scanned in a two-dimensional fashion they can do
that with a slit as well and how report here some results from this slit scanning that we've done so the the types of energy that we use a written up here with copying a 30 by 20 cm hologram choose into these wavelengths very carefully and then afterwards the copy shifted down 20 nanometers to be more visible and in color corrected so that would serve of 50 millimetres and we plot here the time to write the entire hologram versus the relative efficiency to the master and you can see that I want to deal with the the the form of these graphs which is statistically significant by the way but as you increase the time you also increase the overlaps because your overlapping the slits at each time and the diffraction efficiency generally progresses the more you overlaps and you can see from the brain you getting up to near 100 % of the red is slightly less than the blue slightly less
this is making coincident points let's you recall holograms at the same time and you can also call this is an overlap versus the relative efficiency and
basically the results the following that with without white slept with that you can master you can get around 50 to 70 % average diffraction efficiency relative efficiency which is a little bit less than what you need really commercially we'd like to get 110 descendants use a single color you can get up to 300 % so there's a big difference there but if you use time cocking to 1st use sleep with red the green then below you can get to nearly 90 % so you can get pretty commercial results interesting if you do it in the opposite direction I think we've heard this already In this conference from several people if you do it in the opposite direction and use blue 1st you do not get such a good result at all if you copy with blue 1st typically we're getting 50 to 60 % efficiency
so regarding Joe's technology copying with a pulsed laser and kind conclusions now answer it is almost at a commercial level and and we expect really commercial results very very soon the 1 thing that we would and we are trying to we would like to try and we are trapping is using a double their motion because if we can put the 2 great things we can to grating separately we feel we can get that extra diffraction efficiency to make the difference then of copying these types of holograms effectively you can copy them them very very quickly see a few minutes potentially for a hologram like this and if you can get the quality good and the diffraction efficiency good then we see a large market for that and but you until you
thank thank you and all presentation I assume we may have some questions following however you want to write this how you define diffraction efficiency of you're getting 3 100 per cent the fraction of it yeah that's it so we can as its I guess that's a loose definition that what we're doing is we're measuring the brightness of the hologram using them as essentially a power so we're measuring the power but we get you know we set up a system which eliminates the hologram we measured in the power we get From the replay on the master and then on the copy of we divide the 2 so it's a ratio of the replay powers if you like so when I say 300 % means that the the power that you get when you replay the final copy is 3 times greater than the same in the same geometry replace system on the last and thank you for this yeah yet on this little little the what will be the same thing this this is a single layer of all they might so if you need to get some but then that is yes the so you can go with a this because if you're not only motion for FIL being and separately uh we think this will be a piece the balance wall initial thickness of flow function to but sticking might also because people would be very difficult both datasets resulting fossil of the optimal policy will collide players is they might as well more my question is about the thickness of you what you know that's obviously a very good question and is not the 1st time that we've tried to double their emotions we've tried in the past to produce them and that when we were producing the original PSG 3 emulsion for these projects we were very hopeful to get a double their motion and she he didn't work as well as we thought it would work however we probably spend too little time on that so what we're doing now is we will try and do a variety of different tests 1 of the things that I think we feel is that you can do theoretical calculations on all of these things there are a number of variables and it's difficult to say what's gonna work at the end what when we produce the 1st panchromatic material it was very empirical was trying this trying that was wasn't some mathematical calculation so point taken that we are approach would be to try several different batches several thicknesses etc. and see if we can get some better results the beginning of the end of you like the next speaker is and a ready and he will you want to use your computer so in the meantime when you said that a lot of and some more questions about what the question wrong you can use you and you partners was controlled by the state of the art so 1 must be what's also agreed on the rules this is what you would come in the thinking of the using today as 1 of blue green and 1 for Blu-ray and of course yes if I thought that you have incorrectly who questions the 1st these these possible to use a single the old lady there is to do the work you leave the room linking work not supposedly there's just a variety of field later OK this the 1st question the 2nd question is what is the difference you have just described to us the printer's widely used this cholera parameters that are able to recover only the 2nd we have 3 collars printers this week so ecology there's combined together to bring the what difference this with 1 so the 1st question and not call yeah I think the that the the issue is you're asking me if you can use a small CW laser to do this and yeah but the problem is that with CW lasers you have vibration and also that you move your film rapidly if you want to think about metrics all these type of holograms very rapidly and this was also what do you think you can't way yeah I mean in principle you can do that you just have to take a long time to do it on and it you can do contact cooking of course with CW lasers so perhaps I would say that the diode lasers and more useful as CW in the copying because there generally you want to overlap just let's which means that you need inference parametric stability but because the copy and the master is so close together it's very stable anyway so CW lasers a very useful you don't need much energy on the the writing this type of master say it's not so useful yet there you are I think maybe we talk with his hands as saying we should close to you I think what we can have some more questions at the end of the session if you have time before for lunch for all of he gives because they were there thank you very much for this interesting and was b and if