Holographic Film Research Articles

A point diffraction interferometer with random-dot filter

The characteristics and performance of a point diffraction interferometer with random-dot filter are analyzed in detail. Such interferometers are of simple construction and easy to align, and can be used to accurately measure optical wavefronts. The characteristics of the instrument are treated theoretically and analyzed by computer simulation. An experimental system is also constructed to confirm the theoretical results. It is found that the filter should be prepared to have a large number of dots using a high-resolution, low-granularity film such as holographic film in order to obtain a good fringe pattern with minimal noise.

Holographic Gratings in Photosensitive Acrylic Polymers with High Refractive Index Diphenyl Sulfide

To investigate the effects of polymer matrices on the diffraction efficiency of holographic grating, a series of chiral compounds of bornyl acrylate (BA), bornyl methacrylate (BMA), and their enantiomers derived from borneol were synthesized. Instead of conventional liquid crystals, in this investigation we used a high refractive index diphenyl sulfide (DS, n20D=1.6327) mixed with initiators, bornyl acrylate, bornyl methacrylate, and multifunctional monomers to prepare the photosensitive holographic grating films. Membranes having a large refractive index difference (Δn) between the cured grating arrays and revealing high diffraction efficiency (DE) were created by using the compositions. The dynamic formation of the holographic grating and the dependence of the diffracting efficiency on laser exposure time and intensity were carried out. It was found that the intensity of the writing laser may affect the polymerization rate leading to various results of holographic grating. Bragg grating and Raman–Nath grating depending on the incident writing angles were all obtained. We also investigated the plural recording function of the photosensitive films, the morphologies of the polymer matrices, and laser light grating through the holographic grating membranes. Thermogravimetric analyses of the photosensitive membranes were also estimated.

Light-diffusion mark constituted with two-dimensional speckle patterns for enhancing hologram anticounterfeiting characteristics

We propose a new speckle method for enhancing the anticounterfeiting ability of holograms. The method adds light-diffusion marks on holograms. These marks are constituted with periodic speckle patterns. The size of element patterns is very small, so a microscope must be used to check the 2-D microstructure of a mark. When a laser beam illuminates a light-diffusion mark, the diffused light produces a special matrix intensity distribution. Because it is difficult to create an identical random speckle arrangement using different process setups, the matrix intensity distribution diffracted from a specially created light-diffusion mark is nearly impossible to counterfeit. Although holographic films possess birefringent phenomena, the diffraction efficiencies of marks that fit some confinement conditions can be kept stable for light with different polarizations. The proposed method is a good choice for enhancing hologram anticounterfeiting characteristics.

Effects of the chirality and functionality of monomers on the holographic gratings formed in photosensitive films

AbstractPhotosensitive holographic polymer films were fabricated. Instead of liquid crystals, a nonreactive high‐refractive‐index diphenyl sulfide was mixed with several monomers and an initiator for the preparation of the holographic grating films. To investigate the formation of periodic arrays of the photosensitive refractive‐index modulation films and the effects of the chirality and functionality of monomers on the diffraction efficiency, chiral monomeric (−)‐bornyl acrylate, (+)‐bornyl acrylate, and the racemate (±)‐bornyl acrylate were synthesized and copolymerized with various multifunctional monomers. A reasonable schematic of the photosensitive polymerization mechanism was proposed. The effects of the multifunctional monomers, initiator concentrations, and feed monomer concentrations on the diffraction efficiencies were investigated. The morphologies of the polymer matrices were studied with scanning electron microscopy. Pictures of real light diffraction patterns with 15 grating points were obtained. In comparison with those described in the literature, the diffraction efficiency obtained in this investigation was relatively high. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2246–2254, 2003

Holographic optical coherence imaging of tumor spheroids

We present depth-resolved coherence-domain images of living tissue using a dynamic holographic semiconductor film. An AlGaAs photorefractive quantum-well device is used in an adaptive interferometer that records coherent backscattered (image-bearing) light from inside rat osteogenic sarcoma tumor spheroids up to 1 mm in diameter in vitro. The data consist of sequential holographic image frames at successive depths through the tumor represented as a visual video “fly-through.” The images from the tumor spheroids reveal heterogeneous structures presumably caused by necrosis and microcalcifications characteristic of human tumors in their early avascular growth.

Diarylethene Materials for Rewritable Volume Holographic DataStorage

The photochromic diarylethene,1,2-bis(2-methyl-5-(4-formylphenyl)-thien-3-yl)perfluorocyclopentene(1a) is studied and its applicable potential in rewritable volumeholographic data storage is verified. Holographic recording films of10-µm thickness have been fabricated. The refractive index modulation(Δn = 1.15×10-3) between the open- and close-ring formsis detected to be large enough so that the films are suitable for theproduction of volume holographic storage. The experiments of anglemultiplexing and rewriting holograms show that the materials are fitfor volume holographic data storage.

Digital Holography for Instantaneous Spray Diagnostics on a Plane

AbstractWe present a measurement technique that is capable of simultaneously determining sizes and positions of multiple transparent droplets in a plane from scattered light features. The technique is largely independent of particle intensity and mutual obscuration. Reflected and refracted light from the droplets in a pulsed laser sheet is recorded holographically to yield the smallest possible probe volume and the largest possible number density. Larger droplets are best analyzed at the image plane; in this case, the droplets appear as two spots (glare points), whose separation is proportional to the droplet diameter. Smaller droplets are easier to analyze at an out‐of‐focus plane, where their images appear as fringe patterns whose spatial frequency is related to droplet size. Photographic techniques allow only one of these planes to be chosen and are therefore not suitable for multidisperse sprays. Optical holography allows to analyze arbitrary depths, but often suffers from low sensitivity and long analysis times. With digital holography, the spray images are captured digitally by a CCD camera and reconstructed numerically; as in optical holography, the particle reconstruction plane can be freely chosen a posteriori to optimize the measurement. We discuss the issues raised by the transition from holographic film to a CCD sensor as the recording medium, and demonstrate the capabilities of the digital technique.

High-speed adaptive interferometer for optical coherence-domain reflectometry through turbid media.

Two-wave mixing in a dynamic holographic film acts as the adaptive beam combiner in a short-coherence interferometer that performs optical coherence-domain reflectometry (OCDR) through turbid media. This approach combines the high spatial resolution and sensitivity of coherence-domain reflectometry with photorefractive quantum-well-based adaptive homodyne detection. A depth resolution of 28 microm and penetration through 16 mean free paths in a turbid medium have been obtained in this adaptive OCDR application.

Holographic material film composed by Norland Noa 65® adhesive

Abstract A new recorder material, with the possibility to apply to record computer holograms is reported. This material is the Norland Optical Adhesive NOA 65 ® , composite by acrylate monomer with mercapto-ester; these adhesives can be applied easily for any substrates such as plastics or glasses without dark room and critical conditions. Due that, their Norland NOA 65 ® adhesive absorption spectra are localized at UV region λ =300. We record with lithographic techniques some grating, showing good diffraction efficiency with 93%. This material has good resolution to make some diffraction gratings. An important characteristic of this photopolymer is that it is not necessary to use the conventional developed process. In our case, this step corresponds only to the cured polymers process. These properties are attractive because they open the possibility to control the phase material modulation with only controling the cured process. The phase modulation of this material is due mainly to refraction index.

Metal ion-sensitive holographic sensors.

Holographic sensors for Na+ and K+ have been fabricated from crown ethers incorporated into polymeric hydrogels. The methacrylate esters of a homologous series of hydroxyether crown ethers were synthesized and copolymerized with hydroxyethyl methacrylate and the cross-linker ethylene dimethacrylate (3 mol %) to form stable hydrogel films (approximately 10 m thick) containing covalently bound (0-97 mol %) 12-crown-4, 15-crown-5, and 18-crown-6 pendant functionalities. The films were transformed into silver-based volume holograms using a diffusion method coupled with a holographic recording using a frequency-doubled Nd:YAG laser. The resulting holographic reflection spectrum was used to characterize the shrinkage and swelling behavior of the holograms as a function of polymer composition and the nature and concentration of alkali, alkaline earth, and NH4+ ions in the test media. Optimized film compositions containing 50 mol % crown ether showed substantial responses (< or = 200 nm) within 30 s at ion concentrations of < or = 30 mM, which could be rationalized on the basis of the known complexation behavior of the crown ethers. An 18-crown-6 holographic film was shown to be able to quantitate K+ concentrations over the physiologically relevant range. It was virtually unaffected by variations in the Na+ background concentration within the normal physiological variation (approximately 0.13-0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.

그레이스케일 마스크를 이용한 미소렌즈 배열의 제작

홀로그래픽 필름으로 제작된 그레이스케일 마스크를 통하여 두꺼운 포토레지스트를 자외선으로 근접 노광하여 주기 300 <TEX>$\mu\textrm{m}$</TEX>, 두께 17 <TEX>$\mu\textrm{m}$</TEX>, 초점거리 2.2 mm인 10<TEX>$\times$</TEX>10 미소렌즈 배열을 제작하였다. 그레이스케일 마스크는 컴퓨터로 설계한 미소렌즈 배열을 필름 출력기를 이용하여 고해상도 흑백 필름에 그레이스케일로 기록 및 현상하고 이를 다시 홀로그래픽 필름에 축소복사(6.6배)하여 제작하였다. 본 제작방법은 저렴한 비용으로 100%에 가까운 fill-factor를 얻을 수 있고, 비구면 렌즈를 구현하기가 쉽다는 장점을 가진다. Some 10<TEX>$\times$</TEX>10 micro-lens arrays of a period of 300 <TEX>${\mu}{\textrm}{m}$</TEX>, a thickness of 17 <TEX>${\mu}{\textrm}{m}$</TEX>, and a focal length of 2.2 mm are fabricated by exposing a thick layer of photoresist through a grayscale mask via UV proximity printing. The grayscale mask is fabricated in a holographic film by reducing (6.6X) a high-resolution black-and-white film where a grayscale patters of a micro-lens array designed by a computer has been written using a film recorder. The proposed method has the advantage of a low fabrication cost, a fill-factor of almost 100% and the ease of realizing an aspheric lens.

Evolution of anisotropic reflection gratings formed in holographic polymer-dispersed liquid crystals

The temporal evolution of an anisotropic reflection grating produced in a holographic polymer-dispersed liquid crystal film is investigated. We find that this type of grating is preceded in time by an isotropic concentration grating, and that the development of the anisotropic grating can be delayed until several seconds after laser exposure. The formation of an anisotropic grating is nearly coincident with the onset of phase separation of liquid crystal and implies a macroscopic ordering of liquid crystal droplet directors. Detailed knowledge of grating evolution may allow in situ control over the polarization sensitivity of the hologram.

Optical behaviour of display performance enhancement films

Abstract The optical properties of holographic display screen enhancement films are investigated. Experimental data show that the on-axis scattering from such films is significantly stronger than the off-axis scattering. The results are modelled using the beam propagation method in two dimensions. Good qualitative comparisons between experimental and theoretical results are obtained.

Optical behaviour of display performance enhancement films

The optical properties of holographic display screen enhancement films are investigated. Experimental data show that the on-axis scattering from such films is significantly stronger than the off-axis scattering. The results are modelled using the beam propagation method in two dimensions. Good qualitative comparisons between experimental and theoretical results are obtained.

Theoretical simulation of holographic polymer-dispersed liquid-crystal films via pattern photopolymerization-induced phase separation.

A theoretical simulation has been performed to elucidate the emergence of nematic domains during pattern photopolymerization-induced phase separation in holographic polymer-dispersed liquid crystals. We consider a reference system consisting of a single-component nematic, namely, 4-n-heptyl-4(')-cyanobiphenyl (T(NI)=42 degrees C), and a polymer network made from multifunctional monomers. To mimic pattern photopolymerization, the reaction rate was varied periodically in space through wave mixing. In the theoretical development, the photopolymerization kinetics was coupled with the time-dependent Ginzburg-Landau model C equations by incorporating the local free energy densities pertaining to isotropic liquid-liquid mixing, nematic ordering, and network elasticity. The simulated morphological patterns in the concentration and orientation order parameter fields show discrete layers of liquid-crystal droplets alternating periodically with polymer-network-rich layers. The Fourier transforms of these patterns show sharp diffraction spots arising from the periodic layers. As the layer thickness is reduced, the liquid-crystal molecules are confined in the narrow stripes. The liquid-crystal domains appear uniform along the stripes, which in turn gives rise to sharper diffraction spots in Fourier space. Of particular interest is that our simulated stratified patterns are in qualitative agreement with reported experimental observations.

Dynamic holography in a broad-area optically pumped vertical GaAs microcavity

A broad-surface-area vertical GaAs microcavity was operated as an adaptive holographic film. The cavity mirrors were transparent to high-energy (millijoules per square centimeter) hologram writing pulses at a wavelength of 730 nm that generated optically pumped gain gratings in a 1-µm-thick active layer of GaAs. The gain gratings were probed with a low-intensity (mW) tunable laser at wavelengths near the GaAs band edge in the high-reflectance bandwidth of the cavity Bragg mirrors. When the structure was designed with low mirror reflectances [(R1R2)1/2=90%] to operate below the lasing threshold, the cavity resonance bandwidth was sufficiently broad to permit homogeneous hologram readout over a large (several square millimeters) area. Diffraction efficiencies of approximately 10% were predicted and approached experimentally. These results represent a first step toward the realization of a holographic vertical-cavity surface-emitting laser structure.

3D bit-oriented optical storage in photopolymers

The bit-oriented data storage of conventional optical disks may be expanded into the third dimension by using microscopic reflection gratings instead of pits. Microgratings are holographically induced in a photopolymer layer. The Bragg selectivity of holographic volume gratings makes the application of multiplexing methods possible. High storage density may be achieved by combining wavelength multiplexing and multilayer storage. Wavelength multiplexing is realized by recording several gratings overlapping with write beams of different wavelengths. All gratings are recorded simultaneously in the same volume element. By translating a photopolymer sample perpendicularly to the laser beam axis during exposure, stripe-shaped microgratings are induced dynamically with constant linear velocity. The length of a grating is defined by the exposure time. Stripe-shaped gratings are required to realize an areal structure of recorded data similar to the pit-land structure of conventional disks that allows us to overtake the progress made in proceeding CD/DVD technology. Experimental results have been obtained for writing and reading of microholograms in different photopolymer materials including DuPont holographic recording films and CROP photopolymers from Polaroid.

Adaptive femtosecond optical pulse combining

We combine two nominal 100 fs pulses into a pulse train using an adaptive holographic quantum-well film as an adaptive pulse combiner in a two-wave mixing geometry. The two pulses in the combined pulse train are phase-locked and are immune to drifting optical path differences or delay times between the two input pulses. The phase is controlled by the choice of center wavelength. The spectrum of the pulse train is equivalent to the spectral interferogram between two ultrafast pulses.

Droplet size effect on the memory-mode operating temperature of smectic-A holographic polymer dispersed liquid crystal

The memory-mode operation of a polymer dispersed liquid crystal (PDLC), which depends on the stiffness of the layer structure in the smectic-A phase, has been analysed by comparing ordinary PDLC and holographic PDLC (HPDLC). Although both PDLC films were fabricated from the same material, the temperature range of the memory-mode operation was lower in the HPDLC than in the ordinary PDLC. In calorimetric analysis, the differential scanning calorimeter curves of the ordinary and holographic PDLC films were the same. Therefore, the liquid-crystal phase does not depend on the structural difference. This suggests that the force exerted against the layer structure of the smectic phase is greater in HPDLC because the droplet size is smaller and the ratio of the surface to volume is higher.

Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications

This review covers a spectrum of optoelectronic properties of and uses for semi-insulating semiconductor heterostructures and thin films, including epilayers and quantum wells. Compensation by doping, implantation, and nonstoichiometric growth are described in terms of the properties of point defects and Fermi level stabilization and pinning. The principal optical and optoelectronic properties of semi-insulating epilayers and heterostructures, such as excitonic electroabsorption of quantum-confined excitons, are described, in addition to optical absorption by metallic or semimetallic precipitates in these layers. Low-temperature grown quantum wells that have an arsenic-rich nonstoichiometry and a supersaturated concentration of grown-in vacancies are discussed. These heterostructures experience transient enhanced diffusion and superlattice disordering. The review discusses the performance of optoelectronic heterostructures and microcavities that contain semi-insulating layers, such as buried heterostructure stripe lasers, vertical cavity surface emitting lasers, and optical electroabsorption modulators. Short time-scale applications arise from the ultrashort carrier lifetimes in semi-insulating materials, such as in photoconductors for terahertz generation, and in saturable absorbers for mode-locking solid state lasers. This review also comprehensively describes the properties and applications of photorefractive heterostructures. The low dark-carrier concentrations of semi-insulating heterostructures make these materials highly sensitive as dynamic holographic thin films that are useful for adaptive optics applications. The high mobilities of free carriers in photorefractive heterostructures produce fast dielectric relaxation rates that allow light-induced space-charge gratings to adapt to rapidly varying optical fringe patterns, canceling out environmental noise during interferometric detection in laser-based ultrasound, and in optical coherence tomography. They are also the functional layers in high-sensitivity dynamic holographic materials that replace static holograms in Fourier imaging systems and in experimental Tbit/s optical systems. Semi-insulating heterostructures and their applications have attained a degree of maturity, but many critical materials science issues remain unexplored.