Optically addressed As50Se50-liquid crystal structure highly sensitive to He-Ne laser radiation

Spectral dependence of photoinduced phase shift in optically addressed light modulator

“…However, a modulator with ΔΦ λ reaching at least (4)(5)π at the wavelength of maximum spectral sensitivity will also be capable of ensuring a phase shift of no less than 2π in a rather wide spectral range, thus representing a broadband modulator. In addition, obtaining a 2π phase shift at the wavelength of maxi mum spectral sensitivity will require a recording radi ation of small power (several dozen μW/cm 2 ).…”

“…Thus, upon passage from recording by blue light to that by red light, the phase shift decreased by four times, in agreement with the approximately four fold decrease in the saturation photocurrent of the given PC layer. Upon replacement of this PC layer by that of As 50 Se 50 with a spectral max imum at 570 nm, a maximum phase shift of ΔΦ λ = 2π was obtained for the recording by He-Ne laser radia tion and the readout at 814 nm [5].…”

Approach to the approximation of the transfer characteristic and correlation response of Fourier holography scheme

“…1), the transfer characteristic (1) with power-law spectra of reference images recorded on a hologram in a limited frequency range determined by the dynamic range of the EC HRS can often be approximated by exponential functions, since a) frequency-contrast characteristics of information input paths, both optical and electronic, usually decrease with increasing frequency [1], i.e. information input paths play the role of additional low-frequency filters ( LFF); b) spatial limitation of the size of the processed information by the aperture of the frame window leads to a weakening of the zero and low-frequency components of the spectrum as a result of the convolution of the spectrum with the Fourier transform of the aperture -" low spatial" frequencies; c) EC HRS, represented by the dependence of the diffraction efficiency on exposure, usually have a sigmoidal form in the area of the direct (increasing) dependence [5][6][7], which causes additional bandpass filtering on the hologramattenuation of the transfer characteristic (1) relative to the reference spectrum in the ranges of both low and high spatial frequencies [4,[8][9][10]; d) additional filtering is also due to the form factor of the hologram [11], which is especially relevant for Fourier holograms and their special caseholographic matched filters, which in reality are matched only in a limited range spatial frequencies, determined both by the dynamic range of the EC HRS, and the conditions for recording the hologramby choosing the frequency of equality of the local amplitudes of the spectrum and the plane reference beam [4,[8][9][10]. In this case, the limited dynamic range of the EC HRS, which usually does not exceed two orders of magnitude, even in the case of a low-frequency hologram, as a rule, results, if not in a rejection, then in a very strong attenuation of zero and extremely low spatial frequencies.…”