Holographic Grating Period Research Articles

Rotational Tuning of a Holographic Grating Period in a Mirrorless Interferometer with a Fixed Photodetector

Within the framework of geometric optics, this study analyzes the rotational tuning of the period of an interference pattern formed by converging light beams on a photodetector that is fixed relative to a mirrorless two-beam interferometer based on a beam-splitting cube. Equations are derived, whose solutions are the dependences of the tuning range on the base position of the initial light beam on the input surface of the cube and on the diameter of this beam. These dependences are obtained for several refractive indices of the cube material, and the significance of this parameter for the characteristics of the interferometer under study is shown.

Effect of holographic grating period on its relaxation in a molecular glassy film

Holographic grating (HG) relaxation has been experimentally studied in 5,5,5-triphenylpentyl 4-((4-(bis(5,5,5-triphenylpentyl)amino) phenyl) diazenyl) benzoate molecular glassy film for HG periods (Λ) of 0.50, 2.0 and 8.6 μm. A strong effect of HG period on its relaxation is found manifesting itself differently in the volume and on the surface. The volume part of HG is fairly stable during 40 days if Λ > 0.50μm whereas the surface part of HG (most probably, surface relief grating) exhibits relaxational self-enhancement which is maximal at Λ = 8.6μm. It is proposed that thermostimulated directional mass transfer in the process of relaxation can be responsible for this relaxational self-enhancement. Weak HG recording and relatively fast HG decay takes place at Λ=0.50 μm. Therefore, effective chromophore photoorientation domain of about 0.2 μm is supposed.

Holographic properties of azobenzene oligomers with differently bonded chromophore groups

AbstractHolographic 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 hexamethylene‐polyurethane 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 (m at 633 nm. The diffraction efficiency of more than 2% and the specific recording energy down to 30 ‐ 60 J/(cm2%) were achieved in both cases. In the case of type I ABO the best results were achieved with 4‐nitronaphtylazobenzene chromophore groups in hexamethylene‐polyurethane 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. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.

Holographic grating recording in azobenzene polymer films

Abstract The photo-induced birefringence grating and the surface grating in azobenzene polymer films were studied. The photo-induced birefringence (about 0.02 at 633 nm) was investigated at various intensities of laser (532 nm) beam. The effect of laser-induced heating has been introduced to the processes of photo-induced reorientation in azo polymer. The holographic grating period and the peak-to-peak value of the sinusoidal surface profile are 0.8 mm and 40 nm, respectively. The maximum diffractive efficiency of the grating is 2%. The mass diffusion responsible for the formation of the surface grating due to the temperature rise is analyzed.

Polarization Dependence of Holographic Grating in Chalcogenide Film

In this work, we have investigated the polarization dependence of and the effect of annealing in chalcogenide Se75Ge25 and As40Ge10Se15S35 thin films, with respect to the holographic grating formation. The film was irradiated by light from a linearly polarized He–Ne laser at λ=633 nm. The holographic grating period is in the film 1.8 µm. The diffraction efficiency of Se75Ge25 thin film is 0.011% in the film of 1 µm thickness and 0.065% in the film of 3 µm thickness in the S-polarization state. For As40Ge10Se15S35 thin film, the diffraction efficiency is 0.22% as recorded in the P-polarization state. The maximum diffraction efficiency increased considerably, from 0.22% to 0.75%, after annealing the As40Ge10Se15S35 thin film at 200°C. This result seems to indicate that the number of defects diminished by annealing of the thin film increase the directional optical expansion effect, which is due to the optical structure change caused by exposure to optical energy.

Diffraction-efficiency oscillations in amorphous As_2S_3 films

An experimental study of the holographic gratings recorded in nonannealed, thermally with time relaxed amorphous As2S3 films by 514.5-nm light in the presence of 632.8-nm readout light is carried out. The dependences of the maximal first-order diffraction efficiency on the holographic grating period was studied in a wide range of periods, from 0.40 to 70.0 µm. A peculiar oscillatory diffraction-efficiency temporal behavior occurring under certain conditions is reported. The obtained results are discussed in terms of photoinduced structural changes, relaxational structural changes, photoinduced anisotropy, and photoinduced recharging of the localized states in the bandgap. The diffraction-efficiency oscillations are explained by the model of annihilating defects and by multiwave mixing in a thin dynamic hologram.

Two-color holographic-grating formation in amorphous As_2S_3 films

A detailed experimental study of the holographic gratings recorded in nonannealed amorphous As2S3 films by 514.5-nm light in the presence of 632.8-nm readout light is carried out. A strong influence of a continuous 632.8-nm readout is found. The dependences of the maximal first-order diffraction efficiency and the corresponding specific recording energy on the holographic grating period were studied in a wide range of periods from 0.40 to 70.0 μm for 2-yr-old films. The obtained results are discussed in terms of photoinduced structural changes, relaxational structural changes, photoinduced anisotropy, and photoinduced recharging of the localized states in the bandgap. The photoinduced sulphur related D-- and D+-center orientation mechanism is proposed to explain the stimulating action of 632.8-nm light.

Influence of the age of amorphous nonannealed As 2S 3 thin films on holographic properties

The dependences of the maximal first order diffraction efficiency and the corresponding specific recording energy on the holographic grating period were studied. Grating period was varied from 0.40 to 70.0 μm. Both fresh and aged films were used. A large holographic recording efficiency decrease in the course of aging is found to take place. These changes are due to the effective film grain size increase caused by the relaxational structural changes and atmospheric oxygen exposure. Results are explained with the aid of stress fields induced by the evaporation and holographic recording. The obtained results can be used to optimize the hologram recording in amorphous chalcogenide films.

Nonlinear exposure dependence of the holographic recording and relaxational structural changes in amorphous As2S3 films

The exposure dependence of holographic recording has been experimentally studied in nonannealed amorphous As2S3 films for small exposures ≤1 J/cm2. The square root of the diffraction efficiency is found to depend nonlinearly on exposure. This nonlinearity increases when the film thickness is increased and the holographic grating period is decreased. No exposure threshold has been found down to exposures of 0.025–0.17 J/cm2, depending on period. Different reasons for the observed nonlinearity are discussed. Nonlinearity is explained in terms of a phenomenological model based on the simultaneous action of the photostructural and relaxational structural changes, and this model has previously been used to explain the existence of relaxational self-enhancement and the intensity threshold for holographic recording in amporphous As2S3 films. The model itself is developed further.

The investigation of volume change of photopolymerization by holography.

The volume of a photopolymerizable medium may be changed after monomer is converted into polymer. One has not yet precise method for measuring a volume change when a photopolymerization reaction occurs in a film. This paper proposes a holographic method for measuring the volume change (that is the thickness change) of a photopolymerizable film. The method relys on the fact that the volume change can cause a holographic grating period change and result in peak replay wavelength shifts. The volume change can be obtained from the Bragg law, compared the experimental result with the theoretical calculated value.