Holographic Recording Properties Research Articles

Holographic Processes Involved in Rhodopsin-Mediated Phototaxis?

Phototaxis is a light-oriented locomotion found from bacteria to marine invertebrates. In many species, the photoreceptors are molecules of rhodopsin, a protein made of seven α-helical structures embedding a chromophore. Light absorption by the rhodopsin chromophore is transduced to modulate cilia motility and, finally, to alter swimming direction of the micro-organisms. Interestingly, it is well established that rhodopsin is endowed with holographic recording properties. Thus, it may be hypothesized that holographic recording of patterns of light coming from the surroundings play a role in the phototactic behaviour. Such putative functions of rhodopsin in the living organisms might be studied by technological tools, similar to those already used to investigate the holographic recording properties of artificially made rhodopsin material. Moreover, phototaxis mediated by rhodopsin might offer a relatively simple paradigm for searching so far unknown holographic–quantum–processes putatively associated with memory and learning of higher living organisms.

Volume holographic recording in nanoparticle–polymer composites doped with multifunctional chain transfer agents

We report on an experimental investigation of the properties of volume holographic recording in photopolymerizable nanoparticle–polymer composites (NPCs) doped with chain transferring multifunctional di- and tri-thiols as chain transfer agents. It is shown that the incorporation of the multifunctional thiols into NPCs more strongly influences on volume holographic recording than that doped with mono-thiol since more chemical reactions involve in the polymer network formation. It is found that, as similar to the case of mono-thiol doping, there exist optimum concentrations of di- and tri-thiols for maximizing the saturated refractive index modulation. It is also seen that recording sensitivity monotonically decreases with an increase in multifunctional thiol concentration due to the partial inhibition of the photopolymerization event by excessive thiols.

Characterization of volume holographic recording in photopolymerizable nanoparticle-(thiol-ene) polymer composites at 404 nm

We report on the photopolymerization dynamics and the volume holographic recording properties of a thiol-ene based nanoparticle-polymer composite (NPC) doped with a blue-sensitive photoinitiator, Darocur® TPO, by using a highly coherent blue diode laser operating at a wavelength of 404 nm. Our study indicates that volume gratings recorded in the NPC amount to meeting the material requirements of refractive index modulation and material recording sensitivity for holographic data storage media. It is also found that polymerization shrinkage of recorded NPC gratings is higher than that of the same thiol-ene based NPC with a green (523 nm)-sensitive photoinitiator, Irgacure® 784/BzO2. We attribute such a difference in shrinkage to the photopolymerization dynamics at these recording wavelengths. We show that this shrinkage increase at 404 nm can be mitigated to some extent by controlling the thiol-ene stoichiometry in the NPC.

Blue laser-sensitized photopolymer for a holographic high density data storage system

We present a new blue-sensitized photopolymer to achieve a higher storage density compared to green/red-recordable media. Photopolymers are prepared based on a two-chemistry system and their holographic recording properties are investigated. A matrix of long and flexible ether units of an epoxy precursor and a multi-crosslinkable amine hardener enhances energetic sensitivity and suppresses volume shrinkage effectively. Page-wise recording of 961 bits/page of digital data is demonstrated and long term recording stability is also verified for a period of roughly 2 months.

Holographic testing of fluorescent photosensitive glass–ceramics

In this paper we investigate the holographic recording properties of the fluorescent photosensitive glass–ceramics. The materials described here, stable up to 400 °C, represent a substantial advancement in the development of long lifetime media for holographic data storage. A detailed physical–chemical characterization of the proposed material is presented. It is shown that volume holograms were obtained after the recording process using a continuum high power laser in an off-axis setup.

Investigation of the light induced redistribution of zeolite Beta nanoparticles in an acrylamide-based photopolymer

We report the redistribution of colloidal zeolite Beta nanoparticles during holographic recording in acrylamide-based photopolymers. Using the techniques of confocal Raman spectroscopy and scanning electron microscopy coupled with energy dispersive x-ray analysis (SEM–EDX), we have observed a periodic pattern, whose spacing agrees with the fringe spacing of the recorded holographic diffraction grating. It was estimated that the fraction of nanoparticles redistributed as a result of the holographic recording is 40%. The effect of the nanoparticles on the average refractive index of the nanocomposite layers was studied by UV–visible spectroscopy. It was observed that the addition of zeolite nanoparticles leads to an increase of the photopolymer layer's thickness, and this is ascribed to the interaction between molecules of monomer and the zeolite nanoparticles, further supported by Raman spectroscopic studies, indicating that these nanoparticles are not an entirely inert additive. The holographic recording properties of the new nanocomposite were characterized and no significant improvement of the net refractive index modulation was observed. This result is explained after taking into account two main factors influencing the final refractive index modulation—the redistribution of the nanoparticles and the change in the monomer's volume concentration due to change in the thickness of the solid layers. The results presented here contribute to insights about the role of nanoparticles in the mechanism of holographic recording in acrylamide-based photopolymeric systems. The zeolite nanoparticle redistribution achieved in this new nanocomposite could be useful for the fabrication of holographic sensors, as demonstrated by initial studies with toluene.

Structural transformations in amorphous As x Se1−x (0 ≤ x ≤ 0.20) films

Structural transformations are examined by the employment of Raman scattering measurements for amorphous Se-rich As x Se1−x (0 ≤ x ≤ 0.2) alloys. It is found that the molecular structure of amorphous Se (a-Se) on the scale of medium-range order differs from the structure of most inorganic glasses and may be placed between 3-dimensional network glasses and polymeric ones. Further experiments show the existence of successive phases in laser-induced glass—crystalline transition with pronounced threshold behavior. By comparing peak width, peak location and Raman intensity in the range of bond modes it is derived that the changes occur not monotonically with increasing As content. The composition-induced changes of the spectra are explained by cross-linking of Se chains. Under laser irradiation, the changes in the optical transmission, holographic recording properties and Raman spectra of amorphous As x Se1−x films with 0 < x ≤ 0.2 have been examined. The dependence of the transmissivity and diffraction efficiency on the irradiation energy density shows two qualitatively different regions. Below the energy density threshold, E th, only small changes in the local structure of the system can be detected. In the low-energy region, transient changes in transmissivity are observed. Qualitative explanation of this behavior may be based on associating such with alternating of deep defect states. Above E th, the changes were attributed to crystallization transformation. The corresponding Raman spectra reveal transformation of the system from amorphous into the crystalline phase under laser irradiation. Although several articles and texts have provided reviews on various properties and applications of chalcogenide glasses, there is no thorough study of local atomic structure and its modification for Se-rich amorphous As x Se1−x . The present paper is concerned with this problem.

Structure and optical damage resistance of near-stoichiometric Zn:Fe:LiNbO 3 crystals

A series of near-stoichiometric Zn:Fe:LiNbO 3 crystals were grown by the high-temperature top-seed solution growth (HTTSSG) method from stoichiometric melts doped with 6 mol% K 2O. Infrared (IR) transmission spectra were measured and discussed in terms of the defect structure of the near-stoichiometric Zn:Fe:LiNbO 3 crystals. The results of the transmitted beam pattern distortion method show that the optical damage resistance of the near-stoichiometric Zn:Fe:LiNbO 3 crystals increases rapidly when the ZnO concentration exceeds a threshold value. The threshold value concentration of ZnO of the near-stoichiometric Zn:Fe:LiNbO 3 crystals is much lower than that of the congruent LiNbO 3 crystals. The dependence of the optical damage resistance on the defect structure of the near-stoichiometric Zn:Fe:LiNbO 3 crystals are discussed, and the holographic recording properties of the near-stoichiometric Zn:Fe:LiNbO 3 crystals are investigated.

Optical holographic recording properties of l-(2-Pyridylazo)-2-Naphthol thin film

The optical holographic recording properties of the azo dye l-(2-Pyridylazo)-2-Naphthol in PMMA thin film were studied by using the three-dimensional forward degenerate four-wave mixing technique with a ps pulse laser at 532nm. It demonstrated that the transient grating turned into a permanent grating with the increase of the pulse energy and the grating can be erased through a thermal treatment of the film. The mechanism of the fixed grating was attributed to the trans–cis isomerization of the azo molecules induced by singlet excited-state absorption and the subsequent orientation of the molecules.

Effect of wavelength of sensitizing light on holographic storage properties in LiNbO3:Fe:Ni crystal

By sensitizing with 514nm green light, 488nm blue light and 390nm ultraviolet light, respectively, recording with 633nm red light, effect of wavelength of sensitizing light on holographic storage properties in LiNbO3:Fe:Ni crystal is investigated in detail. It is shown that by shortening the wavelength of sensitizing light gradually, nonvolatile holographic recording properties of oxidized LiNbO3:Fe:Ni crystal is optimized gradually, 390nm ultraviolet light is the best as the sensitizing light. Considering the absorption of sensitizing light, to obtain the best performance in two-center holographic recording we must choose a sensitizing wavelength that is long enough to prevent unwanted absorptions (band-to-band, etc.) and short enough to result in efficient sensitization from the deep traps. So in practice a trade-off is always needed. Explanation is presented theoretically.

Absorption characteristic and nonvolatile holographic recording in LiNbO_3:Cr:Cu crystals

The absorption characteristic of lithium niobate crystals doped with chromium and copper (Cr and Cu) is investigated. We find that there are two apparent absorption bands for LiNbO3:Cr:Cu crystal doped with 0.14 wt.% Cr2O3 and 0.011 wt.% CuO; one is around 480 nm, and the other is around 660 nm. With a decrease in the doping composition of Cr and an increase in the doping composition of Cu, no apparent absorption band in the shorter wavelength range exists. The higher the doping level of Cr, the larger the absorbance around 660 nm. Although a 633 nm red light is located in the absorption band around 660 nm, the absorption at 633 nm does not help the photorefractive process; i.e., unlike other doubly doped crystals, for example, LiNbO3:Fe:Mn crystal, a nonvolatile holographic recording can be realized by a 633 nm red light as the recording light and a 390 nm UV light as the sensitizing light. For LiNbO3:Cr:Cu crystals, by changing the recording light from a 633 nm red light to a 514 nm green light, sensitizing with a 390 nm UV light and a 488 nm blue light, respectively, a nonvolatile holographic recording can be realized. Doping the appropriate Cr (for example, NCr = 2.795 x 10(25) m(-3) and NCr/NCu = 1) benefits the improvement of holographic recording properties.

Holographic recording and retrieval of polarized light by use of polyester containing cyanoazobenzene units in the side chain

We examined the holographic recording properties of polyester containing cyanoazobenzene units in the side chain. It was revealed that, when a linearly polarized object beam with an arbitrary polarization direction was recorded, the retrieved beam had the same polarization state as that of the object beam, with a constant diffraction efficiency of 0.1. Moreover, two object beams with mutually orthogonal linear polarization could be recorded and retrieved separately from the same area. This is, to our knowledge, the first example of holographic polarization multiplexing. The retrieved images were found to resolve details of ~40line pairs/mm and a 40-mum -pitched checkerboard pattern. The resolution of the system is limited by the CCD cameras that are used. Polarization encoding to increase the storage capacity and (or) the signal-to-noise ratio of holographic data recording is also discussed.

Accelerated optical holographic recording using bis-DNO

The design, synthesis and optical holographic recording properties of bis-DNO are reported. Bis-DNO is composed of two identical azobenzene oligoornithine segments (DNO) connected via a dipeptide linker. The two segments were assembled in a parallel fashion at the two amino groups of the dipeptide linker by Merrifield synthesis. Surprisingly, the response time of films of bis-DNOs was found to be much faster than that of their linear counterparts.

Laser-induced structural transformation of As xSe 1- x thin amorphous films

The changes in the optical and holographic recording properties of amorphous As x Se 1- x films with 0 ≤ x ≤ 0.2 under laser irradiation have been measured. The dependence of the transmissivity and diffraction efficiency on the irradiation energy density shows two qualitatively different regions. Below an energy density threshold, E th, only small changes in the local structure of the system can be detected. In this low- E region, the transmissivity varies reversibly with exposure. Qualitative explanation of the observed behavior may be based on associating such with alteration of deep defect states. Above E th, the changes were attributed to crystallization transformation. The Raman spectra reveal the progressive transformation of the system from amorphous into the crystalline phase under laser irradiation.

Holographic Recording in Cerium Doped Strontium Barium Niobate a-Axis Single Crystal Fibers

We have grown cerium doped strontium barium niobate (Ce:SBN60) single-crystal fibers, 250 µm-1 mm in diameter, along the a-axis by the laser heated pedestal growth method. The properties of holographic recording in the fiber are investigated. This fiber is expected to have high writing sensitivity due to its large relevant figure of merit and relatively wide grating spacing. The diffraction efficiency reaches more than 40% at 50 ms for a transmitted object beam with an exposure power of 75.2×2 µW. The angular sensitivity is 1.5 mrad at an incident angle of 21°. We also demonstrate image recording in the fiber.

Hole burning, Stark effect, and data storage: 2: holographic recording and detection of spectral holes

The properties of holographic recording and detection of spectral holes in the frequency and electric-field dimension are investigated. To optimize the storage properties of optical memory devices, based on spectral hole burning and holography, cross-talk effects between adjacent holograms have to be minimized. These interactions depend on the relative phases of the holograms chosen during the recording stage. Using free-base chlorin (2,3-dihydroporphyrin) in polyvinyl butyral as host at a temperature of 1.7 K, the influence of the relative phase difference between holograms is demonstrated in both the frequency and the electric-field dimension. Experimental results are presented for rows and columns of holograms stored either in the laser frequency or the electric-field dimension and compared to transmission data. Using both dimensions a 10 x 10 matrix of holograms has been stored within the range of a single wave number.

Measurement of electro-optic and electrogyratory effects in Bi12TiO20

We have conducted measurements of the linear electro-optic coefficient (r41) and electrogyratory coefficient (η41) in Bi12TiO20 at 633 nm. A precise knowledge of these coefficients is important for evaluating the holographic recording properties of this photorefractive material. We have employed both transverse and longitudinal electric field geometries. For each geometry, we present the results of dc as well as ac techniques. Based on these results we find r41=5.75±0.10 pm/V and ‖η41‖≤0.30±0.05 pm/V. We critically examine our measurements and discuss their relative accuracy. Our findings are compared to those previously reported by other investigators.

Influence of the substrate temperature on the holographic properties of Se and SeGe thin films

The effects of the substrate temperature (T(s)) on the optical constants of as-deposited Se and SeGe thin films and on the holographic recording properties of these films were investigated. The substrate temperature held between 35 degrees C and 50 degrees C during thin film deposition was identified as an appropriate means to improve the optical recording properties of these films.

The effect of polymer host on volume phase holographic recording properties

AbstractWe have studied the effect of unsaturated‐polyester and epoxy hosts on the volume phase holographic recording properties of media using camphorquinone and 2, 3‐pentanedione as guests. The sensitivity, determined by holographic diffraction efficiency on exposure to an Ar+ laser, was used as a probe for the chemical behavior of the medium. Intramolecular, photochemical reactions involving 2, 3‐pentanedione in the epoxy hosts are less effective than in the polyesters. For inter‐molecular reactions initiated by photoexcited camphorquinone, media having polyester hosts are again more sensitive. The availability in unsaturated‐polyester hosts of residual monomer for free‐radical addition reactions is a determining factor in the recording mechanism.

Unique Properties of SBN and Their Use in a Layered Optical Memory

Holographic storage experiments using crystal Sr(0.75)Ba(0.25)Nb(2)O(6) (SBN 75/25) as a volume-phase holographic medium show that this material is the most sensitive crystalline storage medium yet discovered. An exposure level of 0.003 J/cm(2) at 0.488 microm produces a 1% diffraction efficiency in a 5-mm length of crystal. In addition to high recording sensitivity, SBN 75-25 exhibits interesting electric-field induced effects that include electric-field enhanced recording sensitivity and voltage-switchable latent-to-active holographic reconstruction efficiency. These effects are explained in terms of drift and diffusion of photoionized carriers coupled with the nonlinear electrooptic behavior characteristic of this low Curie temperature ferroelectric crystal. Detailed measurements of the holographic recording and reconstruction properties of thick phase-volume holograms stored in SBN 75/25 are reported. A mechanism is proposed that correlates the observed electrically controlled holographic response with the dielectric behavior of the crystal. These interesting effects are used to implement a novel, layered optical memory having no moving parts and having electrical access for writing or reading selected layers. An experimental model of the layered memory was constructed to demonstrate the interrelation of the several phenomena involved in the layered concept.