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This paper is dedicated to the study of an AOTF whose selectivity and side lobes are controlled thanks to acoustic square pulses with different and relatively low acoustic power. The behavior of the transmission function of a quasi-collinear acousto-optical tunable filter in TeO_2 is analyzed. The filter is used with acoustic pulses above 12 µs to manipulate the selectivity and with an electric power up to 600 mW to control the side lobes of the filtered spectrum. Using acoustic pulses requires working under a regime of a long optical pulse. The temporal response of the filter was considered to find the best parameters to perform the experiments. The selectivity was controlled from 1.3 nm to 2.5 nm with the use of acoustic pulses. The manipulation of the acoustic power applied to the filter improved the performance of the side lobe levels in regards to the main one from −9dB to −12dB.

During subsequent development of the recently proposed multi-frequency parallel spectrometer for precise spectrum analysis of wideband radio-wave signals, we study potentials of new acousto-optical cells exploiting selected crystalline materials at the limits of their capabilities. Characterizing these wide-aperture cells is non-trivial due to new features inherent in the chosen regime of an advanced non-collinear one-phonon anomalous light scattering by elastic waves with significantly elevated acoustic losses. These features can be observed simpler in uniaxial, tetragonal, and trigonal crystals possessing linear acoustic attenuation. We demonstrate that formerly studied additional degree of freedom, revealed initially for multi-phonon regimes of acousto-optical interaction, can be identified within the one-phonon geometry as well and exploited for designing new cells. We clarify the role of varying the central acoustic frequency and acoustic attenuation using the identified degree of freedom. Therewith, we are strongly restricted by a linear regime of acousto-optical interaction to avoid the origin of multi-phonon processes within carrying out a multi-frequency parallel spectrum analysis of radio-wave signals. Proof-of-principle experiments confirm the developed approaches and illustrate their applicability to innovative technique for an advanced spectrum analysis of wideband radio-wave signals with the improved resolution in an extended frequency range.

We present a principally new acousto-optical cell providing an advanced wideband spectrum analysis of ultra-high frequency radio-wave signals. For the first time, we apply a recently developed approach with the tilt angle to a one-phonon non-collinear anomalous light scattering. In contrast to earlier cases, now one can exploit a regime with the fixed optical wavelength for processing a great number of acoustic frequencies simultaneously in the linear regime. The chosen rutile-crystal combines a moderate acoustic velocity with low acoustic attenuation and allows us wide-band data processing within GHz-frequency acoustic waves. We have created and experimentally tested a 6-cm aperture rutile-made acousto-optical cell providing the central frequency 2.0 GHz, frequency bandwidth ∼0.52  GHz with the frequency resolution about 68.3 kHz, and ∼7620 resolvable spots. A similar cell permits designing an advanced ultra-high-frequency arm within a recently developed multi-band radio-wave acousto-optical spectrometer for astrophysical studies. This spectrometer is intended to operate with a few parallel optical arms for processing the multi-frequency data flows within astrophysical observations. Keeping all the instrument’s advantages of the previous schematic arrangement, now one can create the highest-frequency arm using the developed rutile-based acousto-optical cell. It permits optimizing the performances inherent in that arm via regulation of both the central frequency and the frequency bandwidth for spectrum analysis.

Principally new features of square-law nonlinearity specific to the noncollinear two-phonon acousto-optical interaction (AOI) governed by elastic waves of finite amplitude in birefringent crystals are revealed and studied. An additional degree of freedom represented by the dispersive birefringence factor, which can be distinguished within this nonlinear phenomenon, is found and characterized. This physical degree of freedom gives us a one-of-a-kind opportunity to apply the two-phonon AOI in practice for the first time. The needed theoretical analysis is developed, and proof-of-principle experiments performed with a specially designed unique wide-aperture acousto-optical cell (AOC) made of the calomel (α-Hg_2Cl_2) single crystal, are presented. The results of experiments with this AOC confirm the elaborated theory with numerical estimations and support the proposed application to optical spectrum analysis with the doubled resolution.

The components of dissipative weakly coupled states, originating due to collinear Bragg light scattering by the acoustic wave of finite amplitude, are investigated in the square-law nonlinear medium with the linear optical losses. A novel theoretical model is developed for three-wave weakly coupled states of various pulse profiles, propagating in the quasi-stationary regime with the phase mismatch. The availability of both compact and infinite support is analyzed and compared with one another. Two limiting cases for cnoidal profiles are considered in detail and estimated. Their optical components are observed during the acousto-optical experiments in an α-quartz crystalline cell with calibrated optical losses.

New physical aspects of collinear acousto-optical interaction, occurred by acoustic waves of finite amplitude, are revealed and analyzed in crystalline materials exhibiting moderate linear acoustic losses. The analysis is performed in the regime of continuous traveling waves allowing a specific mechanism of the acousto-optic nonlinearity. Our consideration has shown that such nonlinearity together with linear acoustic losses is able to affect the transmission function inherent in collinear interaction. In particular, the mere presence of linear acoustic losses by themselves leads to broadening the width of the transmission function beginning already from very low levels of the applied acoustic power. Moreover, the transmission function exhibits a marked and quasi-periodical dependence on the applied acoustic power density, and that periodicity is governed by the linear acoustic losses. As a result, the transmission function can be significantly narrowed near isolated points at the cost of decreasing the interaction efficiency. These novelties related to collinear acousto-optical interaction accompanied by moderate linear acoustic losses have been studied and confirmed experimentally with an advanced acousto-optical cell based on calcium molybdate (CaMoO_4) single crystal and controlled by acoustic waves of finite amplitude.