| Popis: |
Practical applications to both ground-based and satellite exploitations have demonstrated that acousto-optical spectrum analyzers of radio-signals represent really reliable signal-processing technique for the millimeter radio-astronomy. These spectrometers provide sufficiently high efficiency of operation together with the frequency resolution needed for astronomic observations. The basic component of similar spectrometer is the acousto-optical cell, whose operation is based on its ability to shape large amount of independent dynamic diffractive gratings. Each of them reproduces the amplitude, frequency, and phase of only one spectral component from the signal under analysis. A multi-pixel CCD linear array detects the obtained responses in Fourier plane of the integrating lens. The main peculiarity of this prototype lies in exploiting a large-aperture tellurium-dioxide crystalline acousto-optical cell, oriented almost along the [001]- and [110]-axes. This cell allows a two-phonon light scattering providing the improved frequency resolution in comparison with conventional one-phonon regime. This fact determines technical requirements to the framing sub-systems and performances of the prototype as a whole. Due to rather high anisotropy of tellurium dioxide, the efficiency of both one- and two-phonon light scattering depends essentially on the ellipticity of the incident light polarization, so that high-efficient operation needs the eigen-state elliptic polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. Currently, an advanced prototype has used a green laser beam at 532 nm with central acoustic frequency about 52 MHz. The first trial experiments in a two-phonon light scattering regime have shown frequency resolution of about 30 KHz. |
