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1SPIE’s International Technical Group Newsletter

HOLOGRAPHY DECEMBER 1999

HolographySPIE’sInternational

TechnicalGroup

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continued on p. 5

VOL. 10, NO. 2 DECEMBER 1999

Instant holographyThe three dimen-sional display ofimages of movingobjects has been adream for many de-cades. Rangingfrom a study of mi-croscopic objects,such as cells, in theirnatural environmentto three dimensionalmovies, this dreamhas been realizedunder certain cir-cumstances. Shortrecordings of mov-ing objects havebeen made holo-graphically in silverhalide films. Butapart from limited sensitivity, this type of re-cording requires the wetprocessing of film.Azobenzene-containing polymers have beenunder intensive investigation during the lastdecade as materials for digital as well as holo-graphic storage. However, since storage inthese polymers involves the physical reorien-tation of long polymer chains, this process wasthought to take place over several seconds, ifnot minutes. We have shown that hologramscan be written in side-chain azobenzene poly-mers with a single pulse lasting 5ns from apulsed laser.1

The cyanoazobenzene side-chain polyester,P3aA, is prepared by transesterification of thecyanoazobenzene containing diol and diphenylpththalate in the melt under vacuum. The diolis prepared in a sequence of reactions startingfrom bromopropyl alkylation of diethylmalonate, reduction to the corresponding1,3-propanediol, ketal protection with ac-etophenone, coupling with cyanoazobenzenephenol and finally deprotection by acidic alco-holysis. Approximately 3 mg of the polyestermaterial is dissolved in 150 microlitres chlo-roform and cast on to a clean substrate. The

film is dried in an oven at a temperature of 90˚Cfor ten minutes.

A polarization holographic set-up is usedto record holographic gratings (Figure 1). Weuse a commercially-available small-frame fre-quency-doubled YAG laser, lasing at 532nm,as the source. This laser delivers Q-switchedpulses of 5-7ns duration at 20 Hz, with a peakpower output of 1.6MW/pulse. A polarizationbeamsplitter (PBS) is used in conjunction withappropriately-oriented quarterwave plates(QWP) to derive the orthogonally polarizedbeams. The two beams overlap on the polyes-

ter film. A HeNe la-ser is used to read-out the diffractiongratings. We findthat after just onepulse from the laser,several orders ofdiffraction of theHeNe laser can beseen. The diffrac-tion efficiency inthe first order ex-ceeds 4% at a spa-tial frequency of160lines/mm.

Significantly, anatomic force micro-scopic scan of the ir-radiated polyester

shows considerable surface relief. A peak-to-valley value of approximately 90nm was ob-tained at a spatial frequency of 900lines/mm.Several groups around the world have observedsurface-relief in azobenzene polymers when ir-radiated with CW laser beams. However, thepresence of a surface relief after just one 5nspulse shows considerable mass redistributionin a short time. Later research, done with col-leagues from the University of Jena, Germany,shows that a surface relief can be obtained withjust a 100ps pulse.

Figure 1. A polarization holographic set-up to record instant holograms. In the figure, PBS, is a polarizationbeam splitter, HWP, half-waveplate, QWP, quarter-waveplate and M, mirror.

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LAB NOTES

Diode laser holographyFor several decades now, the vast majorityof holographic images have been createdusing a continuous-wave gas laser. Rela-tively expensive, cumbersome and ineffi-cient in terms of power-in/power-out ratio,it has always seemed that the gas laser wasjust crying out for it’s own replacement.

The promise of inexpensive, high-powerlaser sources for work in holography hasnow been realized with the availability ofthe latest generation of laser diodes. Holo-grams up to 8×10" in size, with high dif-fraction efficiency and depth, have been cre-ated using sources as inexpensive as $7.99.Currently, power ranges in the visible partof the spectrum of up to 50mW can be ob-tained for less than $50. These are so smallin size that if you dropped one on the floor,you would have to get down on your handsand knees to find it. These higher-powereddiodes are capable of creating bright, deep,display-quality, large-format holograms.

Laser diodes have been in use for a num-ber of years already, and have been replac-ing the traditional gas laser in an increasingnumber of applications (bar code scanners,optical data storage, etc.). One of the lasthold-outs has been holography—wheresingle-mode operation and long coherencelength is a must.

With the newer generation of laser di-odes, along with advancements in driver cir-cuitry design (including optical feedbackcircuits for stability), these small wondersof laser light now exceed their gas prede-cessors in all three areas of importance: co-herence length, stability and price. Throughinterferometric testing in my lab, I havemeasured a 35mW diode out to 14' of co-herence length while maintaining extremelystable, high-contrast fringes. Keep in mindthat this 14' coherence measurement indi-cates a minimum, not a maximum—the ac-tual limit of coherence length is still un-known! This raw diode was $34, or roughlyless than one dollar per milliwatt of outputpower.

The “recent” use of diode lasers for ho-lography began in November of 1998 whenholographer Steve Michael reported the cre-ation of a hologram using an off-the-shelf,

a single-beam setup are the plate and ob-ject, this eliminates the need for large isola-tion tables. Just build a small isolation plat-form for these items and you’re all set. Thehigher diffraction efficiency of the newer re-cording materials allows for great resultswith single-beam transfers (includingimageplane) as well.

After a long dry-spell of new and excit-ing techniques with continuous-wave holog-raphy, diode lasers are providing a wealthof uncharted territory. As output powerscontinue to rise and prices continue to drop,the promise and ability for the creation oflarge-format display holography becomesmore of a reality for those who felt it wasout of reach. In the not-too-distant future,the addition of inexpensive green and bluediode sources will make full-color hologra-phy a reality as well.

Frank DeFreitasE-mail: [email protected]: 610/770-0341

For further information on the wwweb:

The Internet Webseum of Holographyhttp://www.holoworld.comA complete record of all my experiments,from laser pointers to higher-powereddiodes.

3-D Imageryhttp://www.3dimagery.comSteve Michaels site containing his workwith laser pointers and suggested set-ups.

Holography in Norwayhttp://www.techsoft.no/holography/Website containing diode laserexperiments by Vidal Hegdal and RonnyAndreassen including advanced single-beam illumination techniques.

Sam’s Laser FAQhttp://www.misty.com/~don/laserdio.htm#diotocThe laser diode section of the on-line“bible” of lasers and laser technology.

battery-operated laser pointer (with averageoutput power of 35mW). I immediately con-firmed Mr. Michael’s results in my own labafter purchasing a laser pointer at my neigh-borhood drug store. I purchased several addi-tional laser pointers and distributed them toseveral other holographers who also obtainedpositive results using the $7.99 laser source.

In 1999, I have continued to experimentwith higher-powered diode lasers along withcolor control and alternative power sources,including solar energy. (I have a 15mW diodein the lab that operates off of a solar panel out-side an upper-floor window. This charges alead-acid based battery pack that runs the di-ode at 3volts—free energy!). I eventuallypartnered with Sam Savage of Bell Labs,Whippany NJ, in developing our own diodelaser system, taking into account the specialrequirements for holographic image record-ing—long coherence length and ultra-stable,high-contrast fringe recording.

There are a number of factors involved withthis research that require a rethinking of thetraditionally approach to holography. With theadvent of ultralong coherence length, it nolonger becomes necessary to match beam-pathdistances in split-beam recording setups. Justplace your components wherever they are mostconvenient and offer the best subject illumina-tion for recording. This will introduce new andmore creative table geometries, and make moreefficient use of available table surface area.

With the increased diffraction efficiency ofthe newer holographic recording materials,along with the advantages that the new diodelasers bring to the table, single-beam work isbecoming more and more appealing as well.Some laser diodes can be operated without anycollimating optics in place—depending onwhere the photodiode is located in the diodeassembly (some photodiodes in modules relyon reflected light from the collimating optics).Diode operation in this fashion provides a beau-tifully clean spread of laser light—as clean asif the beam had been spatially filtered. Thiseliminates all optical components from thesingle-beam set-up (including expensive spa-tial filters), leaving only the diode itself andthe recording media/object. Since the onlyitems that need to be isolated from vibration in



Self-organizing photorefractive neural networkOver the past few decades there has been agrowing interest in neural networks. Indeedthese systems have been found to be good al-ternatives to traditional computers for solvingcertain problems such as pattern classificationor recognition. They are particularly well-suitedto the processing of complex and/or noisy data.

Neural networks basically consist of a largenumber of elementary processors that work inparallel and are connected to each other. Free-space optics is therefore particularly useful forthe implementation of this kind of systems,thanks to its high connectivity and massive par-allelism. However, very few optical neural net-works with large capacities have yet been built.

Among all possible optical techniques, vol-ume holographic interconnects are most prom-ising because of their potentially high capac-ity. Indeed, holographic memories with 109 datapoints, or equivalent elementary holograms,have already been demonstrated.1 If these ho-lograms are read out every millisecond, we getan equivalent computation of 1012 operationsper second.

To explore the possibilities of holographicinterconnects, we have designed and built a self-organizing neural network producing “topologi-cal maps”.2,3 This kind of system performs theautomatic classification of patterns. The setupuses a laser beam divided into two separate arms(reference and signal). The intensities of thebeams in both arms are modulated thanks to twoferroelectric spatial light modulators (SLMs).The beams recombine and interfere inside aphotorefractive crystal where they write a seriesof holograms (Figure 1). These holograms arethen read out with reference beams to determinethe response of the system. The entire set of read-ing beams constitutes the input pattern. The ad-vantage of using photorefractive materials is thatthey allow us to dynamically write, erase andmodify the holograms.4

During the learning stage, several examplesof patterns are presented to the setup. Whenpresenting a particular input pattern, the CCDcamera detects a diffraction pattern that corre-sponds to the response of the system. Accord-ing to this response, an algorithm implementedin a host computer defines how the hologramsshould be reinforced or erased. At the end ofthe learning stage, each input pattern generatesdiffracted light in a localized area of the cam-era only. The relative locations of the responsesfor different patterns should reflect the corre-lations between these patterns: two responsesshould be closer to each other the more similarthe corresponding input patterns are. This clas-sification is said to preserve the topology ofthe input data. The system actually finds therelevant features in the patterns and uses themto perform the sorting. The classification is

made without any control by the experimenterand requires no prior knowledge of the data.

An example of classification is shown in Fig-ure 2. The input patterns are binary vectors thatcode the characteristics of some animals (size,presence of hairs or feathers, number of legs...).They are taken from Reference 2. Once the learn-ing is complete, each presentation of a patternproduces a diffracted spot. Its location is shownin Figure 2, which represents the CCD array, bythe position of the name of the correspondinganimal. The system succeeded in sorting the ani-mals according to the given characteristics. Forinstance, birds are grouped together and so aremammals. Moreover, predatory birds are closeto predatory mammals.

So far we have been able to classify up to100 patterns, each containing more than 100 fea-tures. The classification sometimes makes localerrors, but the global ordering is good. Some mi-nor problems remain to be solved, but we esti-mate that the capacity of the present setup is al-ready about 1 million interconnect updates persecond, which makes it one of the most power-ful optical neural networks, in terms of capacity,ever built.

Y. Frauel, G. Pauliat, A. Villing, andG. RoosenGroupe Non Linéarités PhotoréfractivesLaboratoire Charles Fabry de l’Institutd’OptiqueUnité Mixte de Recherche 8501 du CentreNational de la Recherche ScientifiqueBat. 503, BP 14791403 Orsay Cedex, FranceE-mail: [email protected]

References1. X. An, D. Psaltis, and G. W. Burr, Thermal fixing

of 10,000 holograms in LiNbO3:Fe, Appl. Opt. 38

(2), p.386, 10 January 1999.2. T. Kohonen, Self-organizing Maps, Springer,

Berlin, 1997.3. Y. Frauel, T. Galstyan, G. Pauliat, A. Villing, and

G. Roosen, Topological map from a photorefractiveself-organizing neural network, Opt. Comm. 135,p. 179, 1 February 1997.

4. D. Psaltis, D. Brady, and K. Wagner, Adaptiveoptical network using photorefractive crystals,Appl. Opt. 27 (9), p. 1752, 1 May 1998.

Figure 1. Photograph of the setup.

Figure 2. Example of classification: input vectorscoding characteristics of animals.



Pixel size limit for a holographic memory systemHolographic data storage provides apromising technology for large-den-sity data storage and large data band-width. The theoretical data storagedensity is at the order of one bit perλ3 inside the photorefractive material.The data access rate can be up toGbytes per second due to the intrin-sic parallelism of holography. Themain barriers for providing a com-mercially competitive holographicmemory system are the bulky systemvolume and cost. These barriers canbe overcome by using phase conju-gate reconstruction and small pixelsize for the spatial light modulator(SLM) and detector array in the ho-lographic memory system. This issomething we are currently studyingat Professor Demetri Psaltis’ Optical Informa-tion Processing Lab at the California Instituteof Technology

Phase conjugation reconstructs the back-propagating signal beams and self-focuses ontothe original images without using a bulky andexpensive imaging system. A compact read/write holographic memory module with phaseconjugate readout has been proposed and ex-tensively analyzed.1,2 The cost of this modulewas studied and compared with current maturesilicon storage and hard disk technologies. Thestudies show that the holographic memory costcompared to DRAM technology is determinedby R/M. Here, M is the number of hologramsmultiplexed inside the photorefractive materialand R is the pixel area of SLM and detectorarray used in the holographic memory com-pared to the pixel area of the silicon storageavailable in the market.

The number of holograms M is limited bythe dynamic range of the material M/# and thephoton budget for the reasonable read/writedata-rate of the system. It is crucial to reduceor keep the ratio R to within a small limit forthe holographic module, especially consider-ing the consistent and fast shrinkage of featuresizes in the silicon industry. With current tech-nology, R is around 16 with 4×4µm pixel areafor SLM and photo sensor and 1×1µm forDRAM cell. However, to keep the ratio R atthis number, the pixel area has to be reduced toaround 1×1µm for holographic memory by thetime DRAM cells shrink down to 0.2×0.2µm.The silicon industry predicts this will happenby 2007.

The minimal pixel size in a holographicmemory system is fundamentally limited by theholographic recording and reconstruction band-width, in addition to the bandwidth of the opti-cal system such as the numerical aperture oflenses, and the interface Fresnel losses. The

holographic recording and reconstruction band-width is caused by the different gratingstrengths recorded due to different grating pe-riods, directions and modulation depths forvarious signal spatial frequencies inside thematerial.3 For our previous holographic mod-ule, which had a LiNbO

3 crystal in a 90˚geom-

etry, we calculated the holographic bandwidthinside the material, with the consid-eration of the interface losses. Thetheoretical simulation indicates thatthe holographic bandwidth is broadenough for submicron feature infor-mation to be recorded and recon-structed with 488nm-wavelengthlight.

Experimental measurement of theholographic bandwidth proved thetheoretical results. Sub-micron holo-graphic features were demonstratedby the recording and reconstructionof a resolution mask with pixel sizesfrom 2×2µm down to 0.2×0.2µm. InFigure 2, (a) shows the direct imageof the mask with an objective lenses(NA 0.65) and (b) shows the phaseconjugate reconstruction of the ho-logram magnified with the same ob-jective lens. The reconstruction im-age shows no degradation from thedirect image of the mask, whichproves the theoretical prediction ofsubmicron feature-recording ability.It also demonstrates the feasibility ofusing pixel sizes down to 1×1µm inholographic memory systems andshows how essential phase conjuga-tion is for removing the expensive,high-quality, large-NA imaginglenses previously required for imag-ing small pixels.

An actual 1×1µm random data

Figure 1. A compact holographic memory module with phaseconjugation.

mask was also used to record holograms in thissystem, and holographic read-out bit-error-ratewas measured at 7×10-5, with an assumption ofGaussian distribution for the ON and OFF pix-els. However, using small pixels raises chal-lenges for the development SLMs and detec-tor arrays with high spatial resolution.

Wenhai LiuMS 136-93, Dept. of Electrical EngineeringCalifornia Institute of TechnologyPasadena, CA 91125Phone: 626/395-3889Fax: 626/568-8437E-mail: [email protected]://optics.caltech.edu

References1. J-J. P. Drolet, E. Chuang, G. Barbastathis, and D.

Psaltis, Compact, integrated dynamic holographicmemory with refreshed holograms, Opt. Lett. 22,p. 552, 1997.

2. E. Chuang, W. Liu, J-J. P. Drolet, and D. PsaltisHolographic Random Access Memory (HRAM),Proc. IEEE 87 (11), pp. 1931-1940, 1999.

3. W. Liu and D. Psaltis, Pixel size limit inholographic memories, Opt. Lett. 24, p. 1340,1999.

Figure 2. (a) The direct image of the mask, magnified by anobjective lens (NA 0.65). (b) The phase conjugate reconstruc-tion of the hologram, magnified by the same lens.

a

b



In order to extend the scope of these inves-tigations for practical holographic applications,the set-up was modified to fabricateFraunhofer-type holograms. The object beamwas expanded to cover a transparency contain-ing the word “Risø”. The size of the object was12mm. A single spherical lens was placed im-mediately behind the object, with the polyes-ter film kept close to the focus of the lens. Theunfocussed reference beam overlapped with theobject beam on the lens, and the resulting ho-logram was approximately 1 mm. The imagewas quite bright and can be viewed with na-ked eye on a screen. The appearance of the im-age is instantaneous, not requiring any chemi-cal processing.

Since the output of the laser was 20Hz, itis, in theory, possible to record a holographicmovie. When a large number of holograms arerequired as in this case, the individual holo-grams must necessarily be small. The holo-graphic set-up shown in Figure 1 makes opti-

Instant holographycontinued from cover

Announcement and Call for Papers

Holography 200010-15 July 2000 • St. Pölten, Austria

World-renowned holographers have been invited to contribute papers on the following topics:

Holography and Art • Recording Materials • Display HolographyHolographic Imaging • Holographic Applications • Security Holography

Holography and Storage Media • Stereograms

Submit abstracts to: Prof. Dr. Werner SOBOTKA • Holography 2000 • Herzogenburgerstrasse 68A-3100 St. Pölten, Austria • Fax: ++43 2742 313 229 • [email protected]

Exhibition: Irmfried Wöber • Holotrend • Kahlenbergstrasse 6 • 3042 Würmla • Fax: ++43 2275 8281 • [email protected]

Chairman: W. SobotkaCochairs: Tung H. Jeong, Hans I. Bjelkhagen, Margaret Benyon

Exhibition and Art Forum: Irmfried Wöber

mum use of the hologram size by receiving thesame range of spatial frequencies from eachpoint on the subject. This results in an imagethat is uniformly resolved over its entire ex-tent.2 In order to view the full object through asmall hologram, we believe that we can makeuse of a technique that was proposed originallyby Leith et al..3 In this case, a large lens, whichneed not be of good quality, is used to recordthe hologram. Large scale Fresnel lenses areavailable commercially. The idea is to preservethe spacebandwidth product of the object in thehologram. A reconstruction of the object isviewed through the same lens. A faithful re-production of the object demands a high reso-lution hologram, which the azobenzene poly-mers are capable of. One disadvantage of thistechnique is that the image can only be viewedby a limited audience. However, we believe thatthis technique will be potentially useful forviewing microscopic objects and in particleimage velocimetry.

P. S. Ramanujam* and S. Hvilsted*Optics and Fluid Dynamics Dept.Risø National LaboratoryDK-4000 Roskilde, DenmarkPhone: +45 4677 4507Fax: +45 4677 4565E-mail: [email protected]

References1. P. S. Ramanujam, M. Pedersen, and S. Hvilsted,

Instant Holography, Appl. Phys. Lett. 74, p. 3227,1999.

2. R. J. Collier, C. B. Burckhardt, and L. H. Lin,Optical Holography, Academic Press, 1971.

3. E. N. Leith, D. B. Brumm, and S. S. H. Hsiao,Holographic Cinematography, Appl. Opt. 11, p.2016, 1972.



Circle-to-point conversion and optical rotary jointsDoppler shifts in the optical spectrum maybe detected either by heterodyne methodsusing coherent sources or by direct detec-tion of filtered and dispersed return light.The coherent method requires diffractionlimited optical trains and a local oscilla-tor. The direct detection method is farmore relaxed, requiring only “photonbucket” collection optics and a series ofblocking filters and etalons to separate thefrequency-shifted light into a radial pat-tern. The direct detection of a Fabry-Perotpattern can best be done with a PMT ormicrochannel plate that has been con-structed to have many equal-area electri-cally-isolated detection rings. Such a de-tector, placed at the image plane, canhandle large fields of view and is good atpreserving precious photons.

A less expensive alternative would bea device that could effectively transformthe output of the etalons into a string offoci spaced correctly to fit into a line offibers or onto a linear-CCD or photo-di-ode array. This device could be called acircle-to-point converter and simply redi-rects all the rays that enter each of the cir-cular annuli into unique off-axis focalpoints. One way to do this is to cut outannular sections of the edges of lenses andpiece them together with appropriate off-sets in their respective focal positions. Anextension of this method would be to cutup plastic Fresnel lenses or diffractivelenses. These devices can also be thoughtof as fractured zone plates, re-assembledfor the purpose of separating and detect-ing the Doppler shift imparted to a nar-row frequency laser pulse by winds ormoving objects. The increments in fre-quency occur in equal area annuli, so thecoarse appearance of such an optic is thatof a zone plate as well. The main purpose forthis optical element is the remote detection ofregional wind speeds.

The same peculiar optical element consti-tutes a kind of optical rotary joint, useful incoupling wideband signals from a spinningplatform to a stationary platform. In this alter-native application, the device is best made witheach annulus being the same width rather thanthe same area. That would make it appear to bea coarse axicon rather than a coarse zone plate.Otherwise, they are, or can be, the very sameoptical element. Each annulus is simply an off-axis focusing DOE or HOE that gets shiftedlaterally by some arbitrary increment betweenzones. Shooting them in a step-and-repeat fash-ion, we would simply change the way they aremasked between exposures.

Figure 1 shows a likely layout of the circle-

to-point pattern and Figure 2 is the correspond-ing rotary joint pattern. The circle-to-point pat-tern is used with full illumination over the aper-ture (designed to have as many as 24 annularregions in a 25mm diameter). The rotary jointwould be used with individual modulated lasersor fibers addressing each zone with only a pen-cil beam. The number of channels would be lim-ited by the size of the beams and the allowablecrosstalk. The focus is shifted conveniently offthe axis of rotation and out of the path of anyzero-order light in both applications.

The method of fabrication and replicationcan be the same for each device. We made unitswith 24 zones as computer-generated binarypatterns recorded directly in photopolymer.They could also have been patterned into photo-resist and dry-etched into silica. We opted toadd a high-frequency carrier to eliminate the

possibility of cross talk from higherorders. Alternatively a correct blazecould have been used at lower fre-quencies so that the parts could eas-ily be fabricated by mechanical rep-lication. We also made the samefunctional units by starting with a ho-lographically-constructed master thatwas subsequently stepped betweenexposures along with a mask of 7 or24 rings. The HOE constructed thisway can then be copied optically inone step into another volume record-ing material for higher volume pro-duction.

The diffractive design and fab-rication of the rotary joints were car-ried out independently by MathiasJohansen and Sverker Hard, atChalmers University of Technologyin Sweden, and the design of thecircle-to-point converter was con-tributed by Matt McGill and othersat Goddard Space Flight Center,with fabrication being done atRalcon development lab. Patentshave been filed for or granted to bothparties, and both are deserving, butI can’t help being amused by the en-tirely coincidental invention of thesame complex diffractive optical el-ement for two widely differentiatedapplications. It makes me wonderhow often such things occur. Opti-cal interconnects is another fieldwhere similar devices may be used,and could be searched for. It wouldnot be a surprise to find the samedevice in the literature of that fieldand possibly also in holographicmemories.

Richard D. RallisonRalcon Dev Lab8501 S 400 W Box 142Paradise, UT 84328Phone: 435/245-4623Fax: 435/245-6672E-mail: [email protected]://www.xmission.com/~ralcon

References1. Matthew J. McGill, M. Marzouk, V. S. Scott, and J.

D. Spinhirne, Holographic circle-to-pointconverter with a particular application for Lidarwork, Opt. Eng. 36, pp. 2171-2175, August 1997.

2. Mathias Johansson and Sverker Hard, Design,fabrication, and evaluation of a multichanneldiffractive optic rotary joint, Appl. Opt. 38 (8),pp. 1302-1310, 10 March 1999.

3. R. D. Rallison, Fractured zone plates for spatialseparation of frequencies, Proc. SPIE 3633, pp.92-102,1999.

Figure 1. Diffractive circle-topoint converter.

Figure 2. Diffractive optical rotary joint.



Large aperture bacteriorhodopsin filmsIn the middle of the1980s, the first reportsappeared describing anew type of optical re-cording material: opticalf i lms made from thebiological photochromeb a c t e r i o r h o d o p s i n(BR).1-2 At that time BR-f i lms were not verymuch more than a curi-osity. The material wasvery expensive and dif-ficult to process, but thepotential of BR as anoptical material was rec-ognized.

In nature, BR acts asa light-driven photonpump3 and converts sun-light into chemical en-ergy, a function that hasbeen optimized duringevolution. The accompa-nying photochromism is,from a biological point ofview, nothing more thana side-effect. For potentialapplications the photo-chromic properties are themost interesting features,but there are also someothers, among them is its efficient light con-version. The quantum efficiency of the primaryphotoreaction of BR is 64%. This means thatonly 1-2 photons are needed to drive a BRmolecule into its photocycle. The spectral shiftof about 150nm between the absorptionmaxima of the bleached (λ

max= 410nm) and un-

bleached material (λmax

= 570nm) is quite large.With yellow and blue light, the BR materialcan be cycled between the two states. Bothwavelengths are in the visible and, unlike manyother photochromic materials, no UV light isneeded. Last but not least is the excellentreversibility of BR-films. They may be usedover and over without noticeable degradation.

All these parameters make the naturallyoccurring BR-form, so-called wildtype BR (orBR-WT), an interesting material for opticalrecording: at least in principle. However, thestorage time of BR-WT films, i.e. the time ittakes for the bleached material to returns ther-mally to the unbleached state, is rather low: inthe millisecond range. High light intensities aretherefore necessary to achieve acceptable con-trast in such a film.

With the appearance of the first mutatedBR,4,5 the variant BR-D96N, this problem wassolved.6 BR-D96N was the first material wherethe tools of gene technology had been used to

modify the physical properties of a biomate-rial for the sole purpose of creating a valuabletechnical material.

Much effort was put into the developmentof BR-D96N films for optical recording.7 TheBR-films can now be used for polarization re-cording, a very useful technique for the im-provement of the signal-to-noise ratio in opti-cal recording with BR-films. Their applicabil-ity for a variety of optical applications has been

demonstrated, among themnonlinear filtering, holo-graphic pattern recognition,associative memories and in-terferometry.8

For several applications itis desired to have the record-ing medium be large: one ex-ample is high-resolution holo-graphic interferometry. Forlensless recording, whichgives the best results in thisrespect, films with dimensionscomparable to the old silverhalide plates are needed. Now4" BR-films can be preparedreliably in good quality and atreasonable cost. Their firstapplication is to serve as re-versible recording media in aholographic camera for non-destructive testing.9

Is a biomaterial like BRcompetitive to synthetic mate-rials for optical recording? Eachof the parameters of BR-filmsmay be reached, or even ex-ceeded, by other materials—but the combination ofreversibility, sensitivity, polar-ization recording etc. is unique.

Norbert HamppInstitute for Physical ChemistryUniversity of MarburgHans-Meerwein-Str. Geb. HD-35032 Marburg, GermanyE-mail: [email protected]

References1. N. N. Vsevolodov and G. R. Ivanitskii, Biophysics

30, p. 962, 1985.2. A. A. Kononenko, E. P. Lukashev, A. V.

Maximychev, S. K. Chamorovsky, A. B. Rubin, S.F. Timashev, and L. N. Chekulaeva, Biochim.Biophys. Acta 850, p. 162, 1986.

3. H. Luecke, B. Schobert, H. T. Richter, J. P. Cartailler,and J. K. Lanyi, Science 286, p. 255, 1999.

4. D. Oesterhelt and G. Krippahl, Ann. Microbiol.(Paris) 134B, p. 137, 1983.

5. H. G. Khorana, M. S. Braiman, B. H. Chao, T. Doi,S. L. Flitsch, M. A. Gilles-Gonzalez, N. R.Hackett, S. S. Karnik, and T. Mogi, Chem. Scr.27B, p. 137, 1987.

6. N. Hampp, C. Bräuchle, and D. Oesterhelt, Proc.Europ. Conf. Biotechn. EIT, p. 124, 1988.

7. N. Hampp, C. Bräuchle, and D. Oesterhelt,Biophys. J. 58, p. 83, 1990.

8. N. Hampp and C. Bräuchle, Studies in OrganicChemistry 40, p. 954,1990.

9. N. Hampp, A. Seitz, T. Juchem, and D. Oesterhelt,Proc. SPIE 3623, p. 243, 1999.

Figure 1. Three generations of BR-films.The earliest films had an aperture of Ø= 16mm in a Ø = 25.4mm mounting.The 90×90mm large-aperture filmscome in a 4" mounting and have anactive area about 40× bigger than theconventional BR-films. The BR-D96Nfilm (left) is completely bleached,whereas the BR-WT film (right) is in itsinitial purple state. The 8"×12" BR-filmin the rear is a prototype.

Figure 2. The FringeMaker™ system for non-destructive testing and vibration analysis uses 4"size BR-films for recording.

Figure 3. View inside the FringeMaker™ showingthe mounting of the BR-film and the other opticalcomponents.

Table 1. Optical and holographic properties oflarge aperture BR-D96N-films

spectral range recording 520-640 nmerasure 400-430 nm

exposure (at 532 nm) 0.1-3 mJ/cm2

polarization recording yesdiffraction efficiency 2-3 %resolution ≥ 5000 lines/mmmounting 100×100×20 mmaperture 90×90 mmoptical density (570 nm) 1-3maximal bleaching ratio 95 %thickness of BR film 4.1 mmthickness of BR layer 20-50 µmantireflection coating broadbandreversibility > 106 recordingsshelf life years



Volume phase holographic gratingsfor astronomical spectrographsThe National OpticalAstronomy Observato-ries (NOAO) in Tucson,Arizona, and KaiserOptical Systems, Inc.(KOSI) in Ann Arbor,Michigan, have under-taken a study to evalu-ate the usefulness ofvolume phase holo-graphic (VPH) gratingsfor astronomical appli-cations. Funded by theNational Science Foun-dation, the effort in-volved the fabricationand evaluation of eightdifferent VPH gratings.

VPH gratings differin many ways from theclassical surface relief(SR) gratings currentlyused in astronomicalspectrographs. The lightis diffracted by modula-tions in the refractive index of the grating vol-ume rather than by surface structure. This al-lows a VPH grating to be encapsulated, which,in turn, protects the grating from a variety ofenvironmental factors that might otherwise bedetrimental to surface gratings. The volumeaspect of the VPH grating controls the energyenvelope of the diffracted light by the Braggcondition similar to the diffraction of X-raysby crystalline structures. Very high diffractionefficiencies are possible with VPH gratings thatin some cases can be nearly a factor of twohigher than that achievable with SR gratings.Although this Bragg condition may providehigh efficiencies at a specific wavelengths, itcan unfortunately lead to narrower angular and/or spectral bandwidths for a fixed grating con-figuration than that of a SR grating. However,a VPH grating can be tilted, or tuned, to shiftthe Bragg response to other wavelengths be-yond the design band with efficiencies that canexceed those of the classical SR grating.

Astronomical spectrographs typically re-quire the use of quite large beam diameters.The upper limit has typically been set by theunavailability of SR gratings with sizes largerthan about 200mm. With VPH grating technol-ogy, however, it will be possible to fabricatevery large grating structures (up to 1m) en-abling new concepts in instrumental design.

Another additional benefit is the fact thatVPH gratings can be operated in a true Littrow

configuration. This simplifies the spectrographcamera design since it would no longer have tobe oversized to compensate for the anamorphicmagnification present in a non-Littrow design.

KOSI has also developed a grating conceptthat actually takes advantage of the narrowbandwidths produced by VPH gratings. Theirpatented holoplex element contains two grat-ings within one grating assembly. The first in-teracts with, and diffracts, a specific wavelengthof light. As the wavelength deviates from theBragg condition, the grating diffraction effi-ciency approaches zero at some other wave-length. Through careful process control, KOSIis able to fabricate grating pairs that comple-ment each other in such ways as to diffract twodifferent spectral regions at the same angle ofdiffraction. In other words, one grating diffractsa specific wavelength regime while remaining“invisible” to the light at another spectral re-gion, while the complementary grating has highefficiency at the second spectral region, butminimal efficiency at the first.

The grating produced for the NSF study wasdesigned to diffract both the light of Hydro-gen-alpha (656nm) and Hydrogen-beta(486nm) to the same diffraction angle of 23˚with a 1200 and 1620l/mm grating pair. Al-though this particular grating performs exceed-ingly well, with nearly 93% peak diffractionefficiency at 656nm, the 1200 l/mm compo-nent has a slightly narrower bandwidth than

desired and diffracts15% of the light origi-nally intended for dif-fraction by the 1620 l/mm grating. This lossresults in a peak effi-ciency of only 75% at486nm rather than the90% efficiency pre-dicted. This type of mul-tiplexed VPH is of par-ticular interest in astro-nomical applications inwhich the simultaneousobservation of multiplespectral features is de-sired. Figure 1 showsthe simultaneous spec-tra obtained for a faintblue galaxy with thisparticular NSF grating.

The NSF study isnearing completion asall eight gratings havebeen fabricated and are

currently under analysis. In response to the veryencouraging results achieved by VPH gratings,several observatories around the world(NOAO, Anglo-Australian Observatory, Euro-pean Southern Observatory, etc.) are investi-gating the implementation of VPH gratings inexisting and new astronomical spectrographs.A market demand of 120 gratings is expectedfor the next three year period. This includesVPH gratings ranging in line density from 200-2400l/mm and with sizes of 60-200mm in di-ameter. These gratings are for use in the opti-cal (300-1000nm) and non-thermal infrared (1-1.7µm) spectral regions. Future instruments onthe next generation of telescopes will likelyrequire access to gratings with sizes of 300mmand larger. There is also growing interest inusing this grating technology for the thermalinfrared (1.5-5µm) spectral region if these grat-ings can be shown to operate at liquid nitrogentemperatures.

Samuel C. BardenNational Optical Astronomy Observatories950 N. Cherry Ave.Tucson, AZ 85719Phone: 520/318-8263Fax: 520/318-8360E-mail: [email protected]://www.noao.edu/ets/vpgratings/

Figure 1. A CCD frame of the spectra produced by the holoplex grating is shown to the left. Theextracted hydrogen-alpha and hydrogen-beta spectra of a faint blue compact galaxy are displayed onthe right.



Holoknight ritual held during interferometry ’99A new “Holoknight” was named recently in aceremony performed at the banquet of The In-terferometry ’99 Conference, held in PultuskCastle, near Warsaw. The most recent additionto the International Order of Holoknights wasProfessor Mitsuo Takeda, of the University ofElectro-Communications, who received a tra-ditional sword (A Samurai sword in this case),the symbol of the order. The exclusive orderwas founded in 1988 by Dr. Hans Rottenkolberof Amerang, Germany, a well-known holog-rapher, who also established the original rules.

Each year, the most recently selectedHoloknight selects a well-known holographerfrom the optics community, from a countryother than his own, and one who also has a repu-tation as an excellent international host. Thenew candidate is presented to the group for ap-proval as the next Holoknight to be presentedwith his own sword and parchment in the lan-guage of the selecting Holoknight. Each mem-ber promises to promote and defend the fieldof holography, to promote international friend-ships, and to assist each other in all such en-deavors.

The order now has seven members from fivecountries. “Mitsuo of Tokyo” was selected by“Ole of Trondheim” (Ole Lockberg) and was

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knighted during the banquet by “Werner ofBremen” (Werner Juptner). “Jim of California”(Dr. Jim Trolinger) and “Paul of Alsace” (PaulSmigielski), read Laudatios and letters fromother holoknights to complete the ritual. Thenext Holoknight will be a “Holosamurai” se-lected by “Mitsuo of Tokyo”, and the knight-ing ritual will take place during the San DiegoSPIE meeting in 2000. The selection is keptsecret until the moment of the ritual.

It seems this year that a major challenge forthe new Holoknight was getting the swordthrough the various customs of several coun-tries from Poland to Japan. The new sword rodewith airplane captains, was held in custody forseveral hours in Moscow, and was almost con-fiscated in Japan; however, it now hangs inProfessor Takeda’s office.

James D. TrolingerMetroLaser Inc.18010 Skypark Circle, Suite 100Irvine, CA 92614-6428Phone: 949/553-0688E-mail: [email protected]

Figure 1. Holoknight ritual at Interferometry ’99.Professor Mitsuo Takeda is named “Mitsuo ofTokyo”. Holding the sword (out of the picture) isWerner of Bremen. Officiating were “Jim ofCalifornia”, left, and “Paul of Alsace”, right.



2000Photonics West22-28 January

San Jose Convention CenterSan Jose, California USAIncluding international symposia on• LASE ’00—High-Power Lasers andApplications

• OPTOELECTRONICS ’00—IntegratedDevices and Applications

• BiOS ’00—International Biomedical OpticsSymposium

• SPIE/IS&T’s EI ’00—Electronic Imaging:Science and Technology

Education Program and Short CoursesTechnical Exhibit 25-27 January

International Symposium onMedical Imaging

12-18 FebruaryTown and Country HotelSan Diego, California USATechnical Exhibit: 15-16 February

Calendar 2000 Symposium onNondestructive Evaluation

Techniques for Aging Infrastructure &Manufacturing4-10 MarchNewport Beach Marriott Hotel and Tennis ClubNewport Beach, CaliforniaTechnical Exhibit: 29 Feb. - 1 March

Int’l Conference on Trends in OpticalNondestructive Testing3-6 MayLugano, SwitzerlandContact: Pramod K. Rastogi, IMAC, DGC, SwissFederal Institute of Technology Lausanne, 1015Lausanne, Switzerland. Phone: ++41-21-6932445.Fax: ++41-21-6934748. E-mail: [email protected]

SID Symposium 200014-19 MayLong Beach, California USAContact: Society for Information Display, 1526Brookhollow Dr., Ste. 82, Santa Ana, CA 92705-5421 USA. Phone: (1) 714/545-1526. Fax: (1) 714/545-1547. E-mail: [email protected]. Web: www.sid.org

Optical Science, Engineering, andInstrumentation

SPIE’s Annual Meeting30 July - 4 AugustSan Diego Convention CenterSan Diego, California, USATechnical Exhibit: 1-3 August

Holography 200010-15 July 2000

St. Pölten, AustriaContact: Prof. Dr. Werner SOBOTKA, Hologra-phy 2000, Herzogenburgerstrasse 68, A-3100 St.Pölten, Austria. Fax: ++43 2742 313 229. E-mail:[email protected]

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HolographyThis newsletter is published semi-annually by SPIE—The International Society for

Optical Engineering for its International Technical Group on Holography.

Technical Group Chair Michael Klug Managing Editor Linda DeLanoTechnical Editor Sunny Bains Advertising Sales Mark Murgittroyd

Articles in this newsletter do not necessarily constitute endorsement or the opinionsof the editors or SPIE. Advertising and copy are subject to acceptance by the editors.

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InstrumentationEngineers

Enlarging the viewing angle ofcomputer-generated hologramsIt has become quite practical to synthesize semi-gigapixel Fresnel-type computer-generated ho-lograms (CGHs) of 3D objects using personalcomputers, because computational power has im-proved dramatically since the 1960s, when theelements were originally proposed.1 This meansthat, if you have a personal computer, you canmake your own CGH. However, it is not easy tooutput the CGH at your home, because the re-quired output resolution is smaller than one mi-cron. This is roughly 50 times higher than theresolution of regular laser printers.

The electron-beam printer is ideal devicefor 3D CGH writing because of its excellentresolution.2,3 Though it is the best device formass production, it is obviously not suitablefor home use. Classical photographic reductionis often used by those requiring an easier wayof fabricating CGHs. If the element is calcu-lated using collimated reference beam, its view-ing angle is equal to or less than its diffractionangle. Therefore, the viewing angle dependson the pixel pitch of the CGH. Since the reso-lution of the photographic film or camera lim-its the diffraction angle, the resulting viewingangle is not enough for binocular viewing.

We are investigating the use of a lenslessFourier hologram4 for the photographic reduc-tion of the CGH because the viewing angle isindependent of the resolution but proportionalto the number of pixel in the hologram.5 Sincethe lensless Fourier hologram is recorded withthe point reference source beside the object, thepoint illumination or converging illuminationmust be located near the hologram for imagereconstruction. This kind of the special illumi-nation is not practical. We have, therefore,made a secondary hologram using a collimatedreference beam and the object beam from thereconstructed image of the lensless Fourier-typeCGH. With this approach, we have obtainedthe holograms with a viewing angle wider than20˚ that can be reconstructed with collimatedwhite- light illumination. The proposed methodcan also be applied to rainbow holograms6, 7 toreduce image blur and computation time.

Figure 1 shows a pairof white-light recon-structed stereoscopic im-ages from a transmissionhologram made by thismethod. The recorded ob-ject is a wire-frame cubeand its size on the holo-gram is 2.8×4.0mm. Thenumber pixels in the mas-ter CGH is 3200×2200(horizontal × vertical) andthe pixel pitch is about5.5µm. The horizontalviewing angle is as wideas 22.6˚, about seventimes wider than that ofthe CGH calculated withcollimated referencebeam. Since the masterCGH is calculated as a fullparallax hologram, aviewer can appreciate ver-tical parallax as well ashorizontal parallax. Wehave also made reflectionholograms and rainbowholograms.

Although, the pro-posed method requiresoptical transfer to make secondary holograms,it can be done automatically with a spatial lightmodulator as the first hologram shown in Fig-ure 2. The final goal of our research is makinghomemade CGHs easier.

Hiroshi Yoshikawa and Mikio YamagishiDepartment of Electronic EngineeringNihon University7-24-1 Narashinodai, FunabashiChiba 274-8501 JapanPhone: +81 474 695391Fax: +81 474 679683E-mail: [email protected]://www.ecs.cst.nihon-u.ac.jp/~hiroshi/

References1. J. P. Waters, Holographic image synthesis utilizing

theoretical method, Appl. Phys. Lett. 9, pp.405-407, 1966.

2. T. Hamano and H. Yoshikawa, Image-type CGH bymeans of e-beam printing, Proc. SPIE 3293, 1998.

3. T. Hamano, M. Kitamura, and H. Yoshikawa,Computer-generated holograms with pulse-widthmodulation for multi-level 3-D images, Proc. SPIE3637, 1999.

4. George W. Stroke, Lensless Fourier-TransformMethod for Optical Holography, Applied PhysicsLetters 6, pp. 201-203, 1965.

5. H. Yoshikawa and M. Yamagishi, Enlargingviewing angle of computergenerated holograms,Proc. SPIE 3749, 1999.

6. S. A. Benton, Hologram reconstructions withextended incoherent sources, J. Opt. Soc. Am. 59,p. 1545A, 1969.

7. H. Yoshikawa and H. Taniguchi, ComputerGenerated Rainbow Hologram, Optical Review 6,pp. 535-538, 1999.

Figure 1. Reconstructed images from the proposed transmission hologram.(a) View from left. (b) View from right.

Figure 2. Schematic setup of the CGH printer.

holography - sunnybains.com€¦ · holography december 1999 spie’sholography international...

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