Holographic Relief Gratings Research Articles

Polymer composition with phenanthrenequinone for recording relief holographic gratings

The formation of periodic reliefs of the thickness of photosensitive polymer layers after recording holographic gratings in them and stimulating material deformations by reversible plasticization in a non-solvent liquid is considered. The phenomenon was studied for the composition of a copolymer with side anthracene groups — phenanthrenquinone. Phenantrenquinone transfers the energy of electronic excitation to oxygen molecules entering through the open surface of the polymer layer which then cause the oxidation of anthracene fragments. Holographic gratings with a period of 2–5 μm were recorded by laser radiation at a wavelength of 532 nm in layers about 1 μm thick. The photoreliefs were formed during the subsequent swelling of the layer in the medium of a hydrocarbon developer. The photosensitized oxidation of the anthracene groups of the new polymer under the action of optical radiation in the spectral range 408–532 nm was studied using the electron absorption spectra. It is shown that approaching the excitation wavelength to the long-wavelength absorption maximum of phenanthrenquinone (410 nm) makes it possible to increase the sensitivity of the material layer by a factor of 15 compared to layers with methylene blue as a photosensitizer. It has been experimentally established that the amplitude of weak periodic reliefs of a deformation nature (height less than 0.01 μm), which appear immediately after the recording of holographic gratings, increases many times during the treatment of the layer with liquid hydrocarbon. Their maximum value reaches 25 % of the thickness of the recording layer. Presumably, the deformation of the inhomogeneously irradiated layer is stimulated by the transfer of the polymer material into a highly elastic state during its swelling. Photoreliefs are stable after drying. Their strength can be increased by photocrosslinking the material as a result of photodimerization of residual anthracene groups under uniform irradiation with light at a wavelength of 365 nm. The non-sinusoidality of the photorelief reduces the diffraction efficiency achievable with total reflection to values less than 0.20. The studied polymer composition can be used to form relief-phase diffractive optical elements by radiation in the blue-green region of the spectrum, provided by a number of high-power laser sources.

Formation and properties of volume and relief holographic gratings in photopolymer materials

Formation and properties of volume and relief holographic gratings in photopolymer materials

Improvement of the Technology for Manufacturing Relief Holographic Gratings on Dichromated Gelatin Irradiated with Short-Wave UV Radiation

Improvement of the Technology for Manufacturing Relief Holographic Gratings on Dichromated Gelatin Irradiated with Short-Wave UV Radiation

Accurate Morphology-Related Diffraction Behavior of Light-Induced Surface Relief Gratings on Azopolymers

Holographic relief gratings can be fabricated directly on the surface of azobenzene-containing materials (or simply azomaterials) without additional development steps. Despite often being described to have ideal sinusoidal profiles, the developing surface morphology in large amplitude gratings can affect the light distribution of the writing interferogram, causing profile deformations and deviations in the expected diffraction behavior. In this work, we characterize the temporal evolution of the surface relief grating (SRG) morphology fabricated by means of interference lithography on azopolymer films, quantitatively relating the results of a Fourier analysis of their surface profiles to the accurate measurement of efficiencies in the transmitted diffraction orders. A reliable surface structuration dynamics is empirically extracted from the analysis and used to formulate a simple but detailed diffraction model that, within the scalar diffraction theory, exhaustively describes the diffraction behavior of real SRGs without the need of complex rigorous electromagnetic theories. Our results add a deeper insight in the quantitative description of the morphology and the diffraction behavior of SRGs, which can contribute to their adoption for operating high-performance, reconfigurable, compact, and lightweight diffractive optical devices.

Improvement of the technology for manufacturing relief holographic gratings on dichromated gelatin irradiated with short-wave UV radiation

A new variant of manufacturing high-frequency holographic gratings with a spatial frequency up to 1500 mm-1 on layers of dichromated gelatin (DCG), in the processing technology of which water procedures are completely excluded, is proposed. The method is based on the use of glacial acetic acid after the photodestruction of layers by exposure to short-wave UV radiation instead of the standard method of processing holographic structures registered by coherent He-Cd laser radiation. In the course of the experiments, relief-phase holographic gratings with high diffraction efficiency up to 64% were obtained, regardless of the thickness of the DCG layers. Keywords: holographic diffraction gratings, dichromated gelatin, short-wave UV radiation, surface relief, diffraction efficiency, glacial acetic acid, isopropanol.

Formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors

The paper presents a study of the formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors. The recording process of holographic gratings at the argon-laser radiation wave length 488 nm and the process of chemical etching that enables the formation of а relief holographic grating are analysed. The optimum conditions for the formation of diffraction gratings in films of arsenic sulfide As2S3 are defined. It is shown that at the 488 nm wave length of an argon laser the optimum exposure comes to ∼5–8 J/cm2. At the recording stage a quasi-phase (relief-phase) grating is formed, with the diffraction efficiency on the order of a few per cent. Etching of the exposed sample with a solution of NaOH alkali in deionised water and isopropanol makes it possible to increase considerably the relief depth and to improve the diffraction efficiency of a thin diffraction grating approximately up to 20 % for the red spectral region, and to approach the maximal value ∼34 % for the near infra-red region. The results of the study considered look promising for the creation of relief holographic gratings which are essential in present-day optical instrument building (production of spectral devices, holographic sights, and the like).

Mechanisms of Generation of Relief High-Frequency Holographic Structures on Dichromated Gelatin Exposed to Shortwave UV Radiation

The application of two types of alternative action on gelatin in the layers of dichromated gelatin (DCG) was considered: structuring with the use of selective light tanning by the radiation of a He–Cd laser ( $$\lambda=440$$ nm) and destruction performed by exposure of layers to short-wave ultraviolet radiation ( $$\lambda<270$$ nm). The crucial role of UV exposure of samples in generating high-frequency relief-phase gratings with diffraction efficiency higher than 50 $$\%$$ on DCG layers thinner than 2 $$\mu$$ m is shown. It is noted that the application of traditional treatment methods of DCG layers leads to smoothened relief due to action of surface tension forces at high spatial frequencies. In addition, significant broadening of the domain of registered spatial frequencies (up to 1500 mm $${}^{-1}$$ ) for recording relief holographic gratings is achieved by applying the modified technique of gelatin treatment based on reduced time of water procedures and by using the isopropanol baths for quick layer dehydration.

High-frequency relief holographic gratings created by exposing dichromated gelatin to short-wave UV radiation

The possibility of creating effective relief holographic gratings with a high spatial frequency of 1500 mm−1 on the layers of dichromated gelatin (DCG) using the destructive effect of short-wave UV radiation on gelatin is shown for the first time.

Design of discretely depth-varying holographic grating for image guide based see-through and near-to-eye displays.

For the see-through and near-to-eye displays, light throughput and uniformity of luminance over the field of view are improved by employing an optical image guide with discretely depth-varying surface relief holographic gratings. In the design process, a newly developed mathematical model, in conjunction with rigorous coupled wave analysis of diffraction efficiency, eliminates massive and time consuming iteration of non-sequential ray tracing but rapidly identifies the depth-varying structure and optimum optical performance. The depth-varying grating based approach achieved a 1.37x improvement in light throughput compared to the conventional depth un-varying design, 315 cd/m2/lm, along with improved uniformity over the field of view of 35 (H) x 20 (V) degrees with an eye box size of 17 (H) x 14 (V) mm.

Perylenediimide-based distributed feedback lasers with holographic relief gratings on dichromated gelatine

One dimensional second-order distributed feedback (DFB) lasers consisting of polystyrene (PS) films doped with a perylenediimide laser dye, deposited over dichromated gelatine (DCG) photoresist layers with solvent resistant relief gratings recorded by holographic lithography, are reported. The advantage of using the grating on DCG in the final device is that the fabrication process is simplified and the grating pattern better preserved, since no etching methods to transfer the grating to another substrate are needed. A very simple model, proposed to explain the experimental waveguide properties, has allowed identifying the waveguide mode at which DFB emission appears, which was the key to optimize the device performance. In the frame of this model, the thickness of the PS and DCG films could be adjusted in order to minimize the laser threshold and to control its wavelength tuneability. The performance of these lasers is comparable to that of recently reported devices based on the same active material, but deposited over high-quality DFB gratings engraved on SiO2 by nanoimprint lithography.

Time-dependent holographic recording in biopolymer DNA-acridine orange films

It is established that DNA films sensitized by organic dyes (for example, acridine orange), subjected to pulsed excitation in the dye absorption band, allow for several types of time-dependent holographic recording. Dynamic holographic gratings on the dye triplet states and thermal and relief-phase holographic gratings of nondestructive type have been recorded. The efficiency and lifetime of these gratings depend strongly on the concentration of dye, the type of its bonding with the biopolymer, and the recording-pulse energy. High-efficiency relief holographic gratings formed due to the structural transformations occurring in the biopolymer matrix when the energy of recording laser pulses dissipates into heat spontaneously and completely (or almost completely) disappear with time at room temperature. Some data on the distribution of acridine orange molecules over binding sites in the DNA matrix are obtained.

Control of the Molecularly Reoriented Direction in Surface Relief Holographic Gratings Using Photoreactive Liquid Crystalline Copolymers

Molecularly oriented surface relief (SR) structures in photo-crosslinkable liquid crystalline copolymer films were fabricated using a 325 nm He–Cd laser with p–p and s–s polarized intensity holographic beams. The SR height increased as the exposure energy increased. In contrast, the molecular orientation structure depended on the exposure dose. For all doses, molecular migration from the lower exposure region to the higher one was due to the difference in the crosslinking density. The SR height reached up to 280 nm for a film that was initially 1.0 µm thick. The diffraction efficiency depended on the fabricated SR grating, while the difference in the molecular reorientation area and the direction of the SR gratings explained the diffraction properties.

Control of the Molecularly Reoriented Direction in Surface Relief Holographic Gratings Using Photoreactive Liquid Crystalline Copolymers

Control of the Molecularly Reoriented Direction in Surface Relief Holographic Gratings Using Photoreactive Liquid Crystalline Copolymers

Photochemically deposited surface relief gratings of an azo-dye-labeled phospholipid from the aqueous phase

Surface relief holographic gratings are fabricated on the polybutadiene-coated walls of a cell filled with an aqueous solution of an azo-dye-labeled phospholipid. A low power (2 mW) 488 nm argon ion laser wavelength is used. Laser-excited azo dye reacts to produce a permanent surface-relief pattern on the polybutadiene substrate. Gratings are recorded for varying concentrations of the phospholipid solution as well as laser intensity. Lithographic masks are used to show that the photochemical pattern on the substrate is an exact replica of the light intensity distribution, and so the technique can be used for holographic recording as well as for biomolecular applications.

Inorganic Materials for Archival Holographic Recording

Inorganic material systems for archival holographic recording are considered. The emphasis is on bleached silver halide emulsions and CdS and Se colloidal solutions. The bleached silver halide emulsions were investigated to determine the salient parameters that influence photolytic stability and diffraction efficiency. The experimental and theoretical investigations reveal that the silver halide grains, the gelatin matrix, and the gelatin matrix voids are contributing to the holographic storage mechanism. By the adsorption of bromine from the processing solutions on the silver halide grains, it is possible to extend the photolytic stability almost indefinitely. By suppressing the influence of the gelatin matrix and the gelatin matrix voids by chemical processing, it is possible to obtain increased diffraction efficiencies reaching 70%. The colloidal solutions were investigated to determine the basic mechanisms for photodepositing ultrathin surface relief holographic gratings. The results reveal that the photodeposition includes primary photoreduction and secondary adsorption controlled processes. A model is developed to predict the spatial frequency response of the colloidal solutions showing that the recorded spatial resolution is limited by the particle sizes.

Tandem of surface relief holographic gratings as a multiple-beam splitter

Tandem of surface relief holographic gratings as a multiple-beam splitter

Tandem of surface relief holographic gratings as a multiple-beam splitter

A new type of 1 × 9 multiple-beam splitter making use of two surface relief holographic gratings in stack is reported. The grating periods differ by a factor of three and the zero and ±1 diffraction orders generated by either grating on normal or slightly oblique incidence of a plane wave have nearly identical diffraction efficiencies. The fundamental feature of the design is the quoted ratio between grating periods rather than the specific choice of the profile shape. Splitters which generate nine beams (diffraction orders) bearing about 90% of the total output power with less than 4% non-uniformity in their diffraction efficiencies were achieved. Possible extension to 9 × 9 multiple-beam splitting using a tandem of crossed grating is addressed, too.

Laser induced periodic structures in porous silicon

Permanent relief holographic gratings with variable modulation depth have been induced in porous Si films using the interference of two beams obtained by a frequency-doubled Nd:YAG laser ( γ = 530 nm) and a conventional optical setup. Consequently, the gratings have been confined in the porous Si film and the diffraction has been observed by reflection. For an angle of 6° between the interfering beams and for diffracted light at 530 and 633 nm, the Raman-Nath condition is fulfilled and we have observed up to 11 diffraction orders (large phase modulation). We assume that the periodic structures are obtained by thermal effects, which appear in porous Si film from very low laser beam fluences.

Holographic recording by photodeposition techniques

Photodeposition is an emerging new thin-film material deposition and optical image patterning technique with photographic recording characteristics. In the past, lasers and incoherent light sources were exploited for photodeposition of various materials in micropatterns. Here we report that photodeposition can also be used for recording holographic relief gratings of 2000 lines/mm and periodically modulated depths of 1 to 20 nm.

Antireflection effect in ultrahigh spatial-frequency holographic relief gratings

An interpretation model for low reflectivity in ultrahigh spatial-frequency holographic relief gratings is proposed. The model is based on the concept that the grating effective index, caused by grating ultrahigh spatial frequency, is graded in the depth direction and forms an antireflective constitution similar to the multilayer coating. Numerical results show that a sinusoidal grating is antireflective over wide groove depth, wavelength and incident angle ranges, and a grating with nearly triangular section, having a circle arc index distribution, has a very low reflectivity, >10(-4)%. Reflectivity vs groove depth, obtained experimentally for a holographically recorded photoresist grating, agrees fairly well with the numerical results.