No abstract

No 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.

No abstract

PACS 42.40. Lx, 42.70.Jk, 42.70.Ln Holographic properties of two types (I and II, specified in the text) of azobenzene oligomers (ABO) have been experimentally studied in the spectral region of low absorption at 633 nm. In the case of type I ABO the chromophore groups were covalently bonded to either tolyl-polyurethane or hexamethylenepolyurethane matrix. In the case of type II ABO azobenzene chromophores were dispersed in polystyrene matrix, and their concentration was varied from 0.005 to 0.200 mol/l. Samples were in the form of 10 µm thick films. In both cases the diffraction efficiency exposure time dependences were measured for the holographic grating period of 2 µm at 633 nm. The diffraction efficiency of more than 2% and the specific recording energy down to 30 -60 J/(cm 2 %) were achieved in both cases. In the case of type I ABO the best results were achieved with 4-nitronaphtylazobenzene chromophore groups in hexamethylenepolyurethane matrix. The chromophore concentration threshold within 0.01 -0.04 mol/l range, the holographic efficiency growth with chromophore concentration and the photosensitization effect were found in the case of type II ABO. 1 Introduction Organic materials have been extensively studied as recording materials for scalar and vector holography [1, 2] because they allow for wider tailoring of properties than inorganic materials. Azocompounds are among the most efficient holographic recording materials, which we have studied, also in previous papers [3]. In this paper we report on further studies of azobenzene oligomers (ABO), for holography in the red spectral region, which is of special theoretical and practical interest. First, the unclear physical mechanism [4] that enables recording in the spectral region with very low absorption is of large interest. Second, the hologram recording in this region allows one to obtain higher diffraction efficiency (DE) and to use cheaper lasers. Two groups of materials have been studied: ABO with covalently bonded chromophore groups (type I ABO) and ABO with dispersed (without the covalent bondings, type II ABO) ones. The matrices were also varied. The polyurethane structure was modified by tolyl (Tl) or hexamethylene (HM) in the case of type I ABO (Fig. 1). (These matrices we further designate as Tl and HM matrices.) Polystyrene matrix was used in the case of type II ABO. Each type of samples has its advantages and disadvantages. Oligomers with chromophore groups covalently bonded to the matrix exhibit higher DE and photosensivity yet the synthesis standardization is difficult. On the contrary, ABO with dispersed chromophore groups until now have exhibited lower holographic efficiency but their synthesis is much easier and more predictable. In this work we show that their efficiency can be comparable to that of the first group.