Recording Of Volume Holograms Research Articles

A New Three-Component Photo-Initiating System for Visible Light Recording of Volume Holograms with Single-Pulsed Laser.

Versatile substituted electron-deficient trichloromethylarenes can easily be synthesized and combined with a Safranine O/triarylalkylborate salt to form a highly efficient three-component photo-initiation system that starts free radical polymerization to finally form holographic gratings with a single-pulsed laser. The mechanism of this photo-initiation most likely relies on an electron transfer from the borate salt into the semi-occupied HOMO of the excited dye molecule Safranine O, which after fragmentation generates an initiating alkyl radical and longer-lived dye radical species. This dye radical is most probably oxidized by the newly introduced trichloromethylarene derivative as an electron acceptor. The two generated radicals from one absorbed photon initiate the photopolymerization and form index gratings in a suitable holographic recording material. This process is purely photonic and does not require further non-photonic post treatments.

Use of forbidden singlet–triplet electron transitions in photopolymer material for holographic recording with high intensity nanosecond laser pulses

The goal of this research is recording of volume holograms in thick photopolymer material, based on the use of forbidden singlet–triplet transitions of the dye-sensitizer with high intensity (up to 12 GW cm−2) nanosecond pulses at λ=532nm. The material has threshold character of recording, that can lead to improved three-dimensional (3D) control of photochemical or photophysical processes. This is especially important for the microholographic approach to 3D multilayer optical data storage. The concentrations of the dye-sensitizer and electron donor in the photopolymer was optimized, and high value of refractive index change of 3.1⋅10−3 was achieved. The sensitivity of the material under research is much higher than the sensitivity of materials using two-photon absorption, which made it possible to record microholograms by a single laser pulse. Using the method of heterodyne detection, we also studied the spatial distribution of the optical inhomogeneity in photopolymer material.

Fast novel nonlinear optical NLC system with local response

Nonlinear optical performance of a novel liquid crystalline (LC) cell has been studied in two-wave mixing experiments revealing high diffraction efficiency within extremely wide intensity range, fast recording times and spatial resolution. Photo-induced modulation of the LC order parameter resulting from trans-cis isomerisation of dye molecules causes consequent changes of refractive indices of the medium (Light-Induced Order Modification, LIOM-mechanism) and is proved to be the main mechanism of optical nonlinearity. The proposed arrangement of the electric-field-stabilised homeotropic alignment hinders the LC director reorientation, prevents appearance of surface effects and ensures the optical cell quality. The LIOM-type nonlinearity, characterised with the substantially local nonlinear optical response, could also be extended for the recording of arbitrary phase profiles as requested in several applications for light-beam manipulation, recording of dynamic volume holograms and photonic lattices.

Optical nonlinearities of small polarons in lithium niobate

An overview of optical nonlinearities of small bound polarons is given, which can occur in the congruently melting composition of LiNbO3. Such polarons decisively influence the linear and nonlinear optical performance of this material that is important for the field of optics and photonics. On the basis of an elementary phenomenological approach, the localization of carriers in a periodic lattice with intrinsic defects is introduced. It is applied to describe the binding energies of four electron and hole small polarons in LiNbO3: small free NbNb4+ polarons, small bound NbLi4+ polarons, small bound NbLi4+:NbNb4+ bipolarons, and small bound O− hole polarons. For the understanding of their linear interaction with light, an optically induced transfer between nearest-neighboring polaronic sites is assumed. It reveals spectrally well separated optical absorption features in the visible and near-infrared spectral range, their small polaron peak energies and lineshapes. Nonlinear interaction of light is assigned to the optical formation of short-lived small polarons as a result of carrier excitation by means of band-to-band transitions. It is accompanied by the appearance of a transient absorption being spectrally constituted by the individual fingerprints of the small polarons involved. The relaxation dynamics of the transients is thermally activated and characterized phenomenologically by a stretched exponential behavior, according to incoherent 3D small polaron hopping between regular and defect sites of the crystal lattice. It is shown that the analysis of the dynamics is a useful tool for revealing the recombination processes between small polarons of different charge. Nonlinear interaction of small polarons with light furthermore results in changes of the index of refraction. Besides its causal relation to the transients via Kramers-Kronig relation, pronounced index changes may occur due to optically generated electric fields modulating the index of refraction via the linear electro-optic effect, also. Based on a microscopic picture and by considering the local structural environment of bound polarons, the appearance of photovoltaic currents is explained straightforwardly as a result of the optically induced carrier transfer. Both transient absorption and index changes are spatially confined to the intensity profile of the interacting light allowing for the recording of efficient mixed absorption and phase volume holograms. By means of holographic spectroscopy, these small-polaron based optical nonlinearities are verified either without or with the action of the linear electro-optic effect; their prominent features are highlighted by appropriate experimental studies wherin the ultrafast response on the picosecond time scale is the most recognized one. Based on these findings, the consequences for applications of LiNbO3 in the field of nonlinear optics and photonics are presented. Besides visionary examples like real-time, 3D holographic displays, the impact of optical nonlinearities of small polarons for present applications are discussed with frequency conversion and respective limiting effects, such as green-induced infrared absorption and optical damage, as important example.

Highly efficient volume hologram multiplexing in thick dye-doped jelly-like gelatin.

Dye-doped jelly-like gelatin is a thick-layer self-developing photosensitive medium that allows single and multiplexed volume phase holograms to be successfully recorded using pulsed laser radiation. In this Letter, we present a method for multiplexed recording of volume holograms in a dye-doped jelly-like gelatin, which provides significant increase in their diffraction efficiency. The method is based on the recovery of the photobleached dye molecule concentration in the hologram recording zone of gel, thanks to molecule diffusion from other unexposed gel areas. As an example, an optical recording of a multiplexed hologram consisting of three superimposed Bragg gratings with mean values of the diffraction efficiency and angular selectivity of ∼75% and ∼21', respectively, is demonstrated by using the proposed method.

Photopolymerizable sol–gel nanocomposites for holographic recording

The research into new photosensitive materials with advanced performance for holographic applications is an active branch in material science and photonics, still challenging the field. We proposed a new class of volume hologram recording materials, sol-gel nanocomposites, with important advantages for various holographic applications, including data storage. Here we review several aspects of different types of photosensitive sol-gel glasses that we have developed. Our photopolymerizable glasses exhibit high refractive index modulation, diffraction efficiencies close to the theoretical maxima, along with low scattering and negligible shrinkage. Beside these and other practical advantages discussed in this paper, our recently developed nanocomposite glass incorporating high refractive index species has enabled fundamental studies of new optical phenomena such as the Pendellosung effect, which was observed for the first time in the optical band.

Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm 2 and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm 2 is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation.

Volume hologram recording in diarylethene doped polymer

Volume hologram recording is implemented experimentally in the bulk of diarylethene dye- doped polymeric host-guest material. A wide range of reciprocity for holographic imaging is demon- strated, ranging from as low as 0.55 mW/cm 2 up to more than 200 mW/cm 2 . At a dye concentration of 2 × 10 -3 M and spatial frequency of 2000 mm -1 , refractive index modulations ∆ n of 2 × 10 -5 at λ = 514.5 nm and 1 × 10 -5 at λ = 830 nm were attained. Increasing the dye concentration to 3.8 × 10 -2 M resulted in higher ∆ n values of 3.8 × 10 -4 at λ = 514.5 nm and 2.1 × 10 -4 at λ = 830 nm. The high fatigue resistance of the dye allows multiple record/erase cycles without degradation. The thermal stability of the dye allows for durability of the recording material at temperatures above 115 ° C. At temperatures above 57 ° C, the hologram is found to exhibit thermal degradation at a rate far exceeding that caused by thermochromism. It is suggested that diffusion of the dye in the polymer matrix is responsible for the increased sensitivity of the hologram to elevated temperatures, which may be applied in reusable holo- graphic thermal sensors.

Photochromism of dihydroindolizines: Part VIII. First holographic image recording based on di- and tetrahydroindolizines photochromes

The photochromic compounds dihydroindolizine (DHI) and tetrahydroindolizines (THIs) containing dicyano and diesters were prepared via nucleophilic addition of the corresponding heterocyclic bases to spirocyclopropenes. These compounds showed good photochromic reactions both in solution and in polymethylmethacrylate (PMMA)-matrix by photo-irradiation. Holographic recording was measured by employing the thin films of PMMA-DHI and PMMA-THI as recording media. The PMMA-films of DHIs 1– 3 were studied with regard to their photochemical switching potential of holograms. In the PMMA-film, these coherent beams were interfering to create a holographic pattern, showing equidistant bright and dark lines. Laser light at 532 nm induced the bleaching processes 1a → 1 and 2a, 3a → 2 , 3 thus writing the pattern as sinusoidal modulated interference intensity in the photochromic material. The photochemical burning of the interference pattern by the processes 2 → 1a and 2a, 3a → 2, 3 is generating the negative holographic pattern in the form of 1 or 3. The positive recording technique showed that 1-PMMA produce a hologram grating employing a λ > 400 nm laser beam with only 1 mW/cm 2 intensity. This was sufficient to generate a holographic grating due to the high-forward quantum yield for 1 → 1a of 0.8. The present results indicate that, the UV-laser generated holograms are produced with lower light intensities compared to the vis-laser process in the negative technique. The recording of volume holograms was achieved on the basis of data and information recording system.

Volume Hologram Recording with Photopolymerization System

Volume Hologram Recording with Photopolymerization System

Cover Picture: TiO2 Nanoparticle–Photopolymer Composites for Volume Holographic Recording (Adv. Funct. Mater. 10/2005)

AbstractTiO2 nanoparticle–photopolymer composites have been employed for volume holographic recording, as reported by Sánchez and co‐workers on p. 1623. Photoinduced segregation of the high refractive index, grafted nanoparticles between polymer‐rich areas leads to improved refractive‐index modulation amplitudes with respect to the base material without nanoparticles. The cover schematically shows a holographic grating registered in this nanocomposite material. These nanocomposite materials should enable the production of holographic optical elements to efficiently control light with angle and wavelength selectivity. This could be used, for example, in liquid‐crystal display technology.A new and efficient photopolymer for the recording of volume holograms is presented. The material comprises a mixture of UV‐sensitive acrylates and grafted titanium dioxide nanoparticles with an average size of 4 nm. We report the formation of holographic gratings with refractive‐index modulation amplitudes of up to 15.5 × 10–3—an improvement of more than a factor of four over the base material without nanoparticles—while maintaining a low level of scattering and a high transparency in the visible‐wavelength range. The influence of the composition of the acrylate system on the final properties of the holographic material is also investigated and discussed. The presence of multifunctional monomers favors the compositional segregation of the different components, while the addition of monofunctional acrylate, highly compatible with the grafting of the nanoparticles, favors the dilution of these nanoparticles.

TiO2 Nanoparticle–Photopolymer Composites for Volume Holographic Recording

AbstractA new and efficient photopolymer for the recording of volume holograms is presented. The material comprises a mixture of UV‐sensitive acrylates and grafted titanium dioxide nanoparticles with an average size of 4 nm. We report the formation of holographic gratings with refractive‐index modulation amplitudes of up to 15.5 × 10–3—an improvement of more than a factor of four over the base material without nanoparticles—while maintaining a low level of scattering and a high transparency in the visible‐wavelength range. The influence of the composition of the acrylate system on the final properties of the holographic material is also investigated and discussed. The presence of multifunctional monomers favors the compositional segregation of the different components, while the addition of monofunctional acrylate, highly compatible with the grafting of the nanoparticles, favors the dilution of these nanoparticles.

Nonlinear refractive index of photo-thermo-refractive glass

Nonlinear properties of a photo-thermo-refractive (PTR) glass are studied and compared with those in fused silica and a conventional optical glass. PTR glass is a new photosensitive medium for high-efficiency phase volume hologram recording which manifests a linear refractive index modulation after exposure to UV radiation followed by thermal treatment. Nonlinear optical properties of PTR glass exposed to femtosecond laser pulses are studied. Diffraction patterns in a propagated laser beam focused in the sample were detected by a CCD, while a nonlinear refractive index was measured by a collinear-orthogonal-polarization-pump-probe (COP3) method. It was found that nonlinear refractive index of PTRG is n 2 = 3.3 × 10 −20 m 2 /W (0.33 ppm cm 2 /GW) which is about the same as for the fused silica. It is important that n 2 in PTR glass does not vary after UV exposure and thermal development.

Kinetics modeling in photosensitive glass

Abstract Kinetics of photoinduced process is studied in a new photosensitive material for volume hologram recording which is a photo-thermo-refractive glass (PTRG). A system of balance equations is derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+)+. The main approach for the system solution is a calculation of low quasistationary concentration of free electrons in a conduction band, while concentrations of generated electron and hole centers are expected to be variable. A general solution of a system is found as a combination of exponential and hyperbolic functions. It is shown that an exponential solution is the result of the absence of a re-trapping of electrons, while a pure hyperbolic solution occurs in the case of equal probability of trapping and re-trapping. The approach developed for the first stage of photo-thermo-refractive process which is photoionization and trapping, is applied for the modeling of the final result of the whole process of photo-thermo-induced refractive index transformation in glass. It is found that the refractive index increment in PTRG is better described by hyperbolic function compare to the exponential one. Kinetic parameters of induced refraction in PTRG are determined.

Comparative study of photo-induced variations of X-ray diffraction and refractive index in photo-thermo-refractive glass

Spontaneous and photo-induced crystallization have been investigated in fluorinated silicate glass by means of X-ray diffraction and optical interferometry. This glass is a photo-sensitive material for high-efficiency phase volume hologram recording. Variations of a refractive index in this glass are controlled by UV irradiation followed by a thermal development which is photo-thermo-refractive (PTR) process. A method of discrimination of weak narrow crystalline lines from a broad diffractive pattern of a vitreous material was developed, and quantitative measurements of small concentrations of crystalline phase in glass matrix were performed. The sensitivity of the method was about 0.01 wt% of crystalline phase of NaF in a silicate glass. This crystalline phase with concentration below 0.1 wt% was detected even in a highly transparent PTR glass with a modified refractive index produced by PTR processing. A correlation between the intensity of X-ray diffraction peaks of NaF and the induced refractive index was found in equally developed PTR glass samples exposed to different dosages of UV radiation.

Field improvement in a uniaxial centered lens composed of two stacked-volume holographic elements

Arrangements are described for the recording of volume holograms with two sections that, when stacked together, work as uniaxial centered lenses and allow one to solve the problem of angular selectivity in the imaging of wide objects. The performance of such systems is examined qualitatively, and suggestions aimed at improving these designs are proposed.

High-efficiency volume hologram recording with a pulsed signal beam

We present an efficient photorefractive volume hologram recording technique with a pulsed signal beam and continuous reference-beam illumination. The grating envelope can be simply controlled by manipulation of the duty cycle of the signal beam. Thus, for any grating coupling strength and different initial reference-signal intensity ratios, the diffraction efficiency can be maximized with this technique and can be greatly increased in comparison with that of the conventional recording technique.

Recording of volume hologram using a beam pattern from tapered optical fiber

A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version.

Very Selective Volume Holograms: Manufacturing and Applications

It is well known that transmissive and reflective type volume holograms have very high angular and spectral selectivity. Such highly selective holograms can find wide application in different fields, namely, three-dimensional imaging, diffraction optical elements, holographic storage, etc. The main problem in manufacturing thick holograms (of about a millimeter thickness) is in developing very thick photosensitive media, in which a grating can be recorded by illumination with an interference pattern. The analysis shows how different kinds of inhomogeneities and material shrinkage cause distortions in the reconstructed image and hologram selectivity properties. A review of the Russian materials (confirmed by experimental data) suitable for the recording of volume holograms is made.

Holographic diffraction gratings recording in organically modified silica gels

The silica gel-methyl methacrylate organically modified ceramic is proposed for recording of volume holograms. Both low-spatial-frequency (54 line pairs/mm(-1)) and high-spatial-frequency (1400 line pairs/mm(-1)) holographic gratings were successfully recorded in the medium by interference of two coherent beams of 351.1-nm wavelength. High diffraction efficiencies (93%) and extremely low absorption and scattering coefficients were measured during the holographic reconstruction by a 632.8-nm He-Ne beam. The optimum UV recording exposure was ~3 J cm(-2). A grating refractive-index modulation amplitude of 1.1 x 10(-4) was achieved. Virtually no changes in diffraction efficiency were observed after thermal-heating, light-curing, and long-term-aging experiments.