Polarization dependence of holographic recording in glassy azocompounds

Abstract

Polarization dependence of holographic grating recording in glassy molecular azobenzene films 8a, 11, and 16 has been experimentally studied at 633 and 532 nm with s-s, p-p, CE-1 and CE-2 circular-elliptic (differing by light electric field rotation directions) recording beam polarizations. Samples 8a and 11 with the simplest chemical structure were the most efficient at 633 nm, and sample 8a was the most efficient at 532 nm. Self-diffraction efficiency (SDE) up to 45% was achieved in 8a with p-p polarized recording beams at 633 nm. Linear p-p polarizations were the most efficient at 633 nm whereas CE-1 polarizations were the best at 532 nm. It was found that the light polarization changes in the process of diffraction depend on chemical composition, wavelength, and exposure time. Vector gratings with SDE up to 25% were recorded in 8a rotating a linear polarization by 90• . Mainly erasure of gratings took place with one beam. Coherent self-enhancement of gratings was observed only for s-p and both CE polarizations in 8a at 532 nm and for s-p polarizations at 633 nm. Atomic force microscopy measurements also were made. The evidence is found for trans-cis photoisomerization holographic recording mechanism at both 532 and 633 nm. Studied films can be applied for production of polarization holographic optical elements and for permanent optical information recording.

Self-Enhancement of Scalar and Vector Holographic Gratings in Azobenzene Molecular Glassy Films

“…Let us discuss these observations. In our previous papers [12] [13] we have come to the conclusion that HG recording in our organic molecular glasses at 532 nm is due to the azochromophore photo orientation in the process of trans-cis photoisomerization with a possible contribution of azochromophore photodegradation via polarization selective photoinduced N-N bond breaking. These processes are accompanied by mass transfer enabled by athermal fluidization [15].…”

“…The absence of SE at Λ = 0.5 µm and λ 1 = λ 2 = 633 nm (Figure 7), most probably, is due to the limited spatial resolution of sample 8a because the maximal DE at normal recording with two beams in this case is also only about 0.2% (SDE measurement was impossible due to the Bragg selectivity) compared to SDE = 45% at Λ = 2.0 µm [12]. Thus HG relaxation processes prevail over the SE ones.…”

“…The SE effect was reported for the first time in 1973 by Gaylord et al [4] for phase holograms in photorefractive LiNbO 3 :Fe crystals. It has been observed also in photochromic KBr crystals [5], sillenite-type photorefractive Bi 12 Ti 0.76 V 0.24 O 20 crystals [6], amorphous chalcogenide As-S, As-Se films [2] [3] [7], dichromated gelatin and polyvinyl alcohol films [8] and photopolymers [9]. Three types of SE can be distinguished: i) coherent SE due to the holographic recording by diffracted waves; ii) incoherent SE due to the contrast and/or transmission increase of a hologram by incoherent light; iii) relaxational (or dark) SE due to the contrast and/or transmission increase of a hologram by thermostimulated relaxation processes.…”

“…Studied azobenzene molecular glasses were synthesized and characterized by our group. They included 8a or 3-(4-(bis(2-(trityloxy)ethyl)amino)phenyl)-2-(4-(2-bromo-4-nitrophenyl) diazenyl)phenyl)acrylonitrile ( Figure 1, studied also in [12]), W-50 or 2-(2-(-4-(-(4-(bis(2-(trityloxy)ethyl)amino)phenyl)diazenyl)styryl)-6-styryl-4H- Figure 1. Chemical structure of 8a or (4(bis(2-(trityloxy)ethyl)amino) phenyl)-2-(4-(2-bromo-4nitrophenyl) diazenyl) phenyl)acrylonitrile molecule.…”

Thermal, glass-forming, nonlinear optical and holographic properties of "push-pull" type azochromophores with triphenyl moieties containing isophorene and pyranylidene fragments

“…Additional insertion of azobenzene fragment in their structures makes them also possible to form holographic volume and surface relief gratings (SRG) after exposure to laser radiation. This physical phenomena could be used for information and holographic data storage [16][17] . Unfortunately, there is still no clear relation between compound organic structures and their thermal, glass-forming and optical properties.…”