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We present an original approach to precise optical spectrum analysis based on combining the nonlinear acousto-optical processing with the cross-disperser technique. This novelty gives us a possibility to overlap all the visible range by the parallel analysis with a gained spectral resolution. For this goal, an advanced rutile-made acousto-optical cell has been designed and tested as dynamic acoustic grating at ultrahigh-frequency to provide the needed slit density to increase the resolving power and the nonlinear apodization to improve the profile of a resolvable spot. Theoretical estimations were developed for low-loss 6-cm rutile-crystal at λ=440 nm, and they show that one can expect the spectral resolution 0.0609 Å, resolving power 72,250, and the number of resolvable spots ∼39,200. The illustrative proof-of-principle experiments with that rutile-crystal-made acousto-optical cell have been carried out. Experimentally we have obtained the spectral resolution ∼0.0815 Å and resolving power ∼54,000.

We study the potentials of a wide-aperture crystalline calomel-made acousto-optical cell. Characterizing this cell is nontrivial due to the chosen regime based on an advanced noncollinear two-phonon light scattering. Recently revealed important features of this phenomenon are essentially exploited in the cell and are investigated in more detail. These features can be observed more easily and simply in tetragonal crystals, e.g., calomel, exhibiting specific acousto-optical nonlinearity caused by the acoustic waves of finite amplitude. This parametric nonlinearity manifests itself at low acoustic powers in calomel possessing linear acoustic attenuation. The formerly identified additional degree of freedom, unique to this regime, is exploited for designing the cell with an eye to doubling the resolution due to two-phonon processes. We clarify the role of varying the central acoustic frequency and acoustic attenuation using that degree of freedom. Then the efficiency of calomel is exploited to expand the cell’s bandwidth with a cost of its efficiency. Proof-of-principle experiments confirm the developed approaches and illustrate their applicability to innovative techniques of optical spectrum analysis with the improved resolution. The achieved spectral resolution of 0.205 A at 405 nm and the resolving power 19,800 are the best for acousto-optical spectrometers dedicated to space or airborne operations to date as far as we know.

We explore the potentiality of using an advanced collinear LiNbO3 acousto-optical filter as a dispersive element for a high-resolution optical spectrograph. Our analysis is focused on weak optical signals in the blue to near-ultraviolet range accessible to ground-based facilities. We examine the phenomenon affecting the filter transmission efficiency and its spectral resolution, namely, the light-induced absorption and photorefraction. A new nonlinear approach is used to determine the performance of this collinear LiNbO3 filter governed by acoustic waves of finite amplitude. The highest available spectral resolution attains δλ=0.15 Å at λ=370 nm (the resolving power R∼25,000), with an efficiency of 11%, or δλ=0.18 Å at λ=532 nm (R∼30,000), with an efficiency of 33%. A slight decrease in the spectral resolution would imply a significant increase in transmission efficiency. Then, we carried out proof of principle experiments with the collinear filter based on the congruent LiNbO3 crystal of 6.3-cm length at λ=405 and 440 nm to verify our analysis and estimations. Potential applications are tackling many issues in astronomy, from detailed abundance analysis in a variety of targets to precise radial velocity measurement.

An opportunity to exploit specific mechanisms of the acousto- optic nonlinearity to regulate performances of the collinear acousto-optical filter, realizing the sequential spectrum analysis of optical signals, is con- sidered. This possibility is theoretically analyzed and experimentally con- firmed with an advanced filter based on calcium molybdate (CaMoO4) single-crystal with a 15-μs time-aperture. It is able to operate over red and near-infrared light at relatively low radio-wave frequencies providing almost lossless regime for controlling acoustic waves of the finite ampli- tude. Under certain conditions, the transmission function of electronically tunable filter exhibits a marked dependence on the applied acoustic power density, and as a result, one can significantly squeeze the transmission function, i.e., improve the spectral resolution of this filter at the cost of decreasing the efficiency of the device partially. The identified and observed non-linear effect makes possible varying the performance data of similar advanced collinear acousto-optical filter governed by external signals of the finite amplitude. © 2013 Society of Photo-Optical Instrumentation