Quasi-collinear IR AOTF based on mercurous halide single crystals for spatio-spectral hyperspectral imaging

Analysis of Phase Mismatch for Mercurous Bromide-Based Non-Collinear AOTF Design in Spectral Imaging Applications

The spectral and spatial characteristics of Acousto-Optic Tunable Filters (AOTFs), such as a tuning curve, spectral resolution, angular aperture, and diffraction efficiency, are determined by the device's acousto-optic crystal configuration and piezoelectric transducer. For high-throughput spectral imaging applications, it is essential to enlarge the spectral bandwidth and angular aperture during the design phase of AOTFs. Thus, phase mismatch due to incident angle or wavelength was studied analytically using phase diagrams in this paper. Additionally, a performance parameter analysis model was established based on the use of mercurous bromide crystals for large angular aperture AOTF device design, and the impact of crystal and transducer design parameters on the spectral bandwidth and angular aperture was evaluated. This also experimentally validates the diffraction capability of AOTFs made from mercurous bromide crystal, which possess a broad spectral transmission ability ranging from visible to long-wave infrared.

Advanced control of an acousto-optic filter performance through arbitrary RF signals

The proposed study consists of using the capabilities of an arbitrary waveform generator to create a specific radio frequency (RF) signal to be applied to an acousto-optic tunable filter based on quasicollinear interaction. By controlling the duration and shape of the acoustic pulse, the filter transmission function can be changed in terms of selectivity and side-lobe levels. The measurement results show good agreement with the simulation model based on the fast Fourier transform. In particular, the Hamming window has been found to be a good option for suppressing side lobes in the transmission function, even when using high acoustic powers.

Broadband Wollaston prism with a large output beam separation based on mercurous halides

The paper proposes a Wollaston-type crystal polarizer suitable for broadband operation within the visible spectral band up to the far infrared band based on unique optical materials, mercurous halides (Hg₂X₂). This paper introduces the general characteristics and optical properties of these birefringent tetragonal optical materials, as well as the general description of a Wollaston prism and the process of its parameter optimization. In general, the Wollaston polarizer is constructed from two combined wedge-shaped prisms. The key parameters that affect the properties of the Wollaston polarizer are then the cut angle of these two prisms and the refractive index of the exploited optical cement (immersion) that bonds the prisms together. The optimal prism cut angles and immersion refractive index are investigated to maximize the Wollaston parameters, such as the transmittance of the polarized radiation and the separation angle of the output orthogonally polarized beams. This process is significantly dependent on the characteristics of all selected mercurous halides (Hg₂Cl₂, Hg₂Br₂, Hg₂I₂). The optimal values of the prism cut angle for each material are selected based on the outlined results. In addition, the Wollaston prism behaviour regarding real radiation propagation is modelled in detail via the Zemax optical studio. The presented models aim to aid in the real design and fabrication of a broadband Wollaston polarizer based on mercurous halides.

Spectral and temporal behavior of a quasi-collinear AOTF in response to acoustic pulses: simulations and experiments

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 TeO₂ 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.

Computational technique for field-of-view expansion in AOTF-based imagers

A rather narrow field of view (FOV) has always been considered as an essential limitation of spectral imagers based on acousto-optical tunable filters (AOTFs). We demonstrate a computational technique to overcome this constraint. It is based on preliminary precise spectral-angular characterization of beam transformation caused by light diffraction on an acoustic wave and consequent correction of acquired stack of spectral images. This technique is applicable for any geometry of acousto-optic interaction and opens the way for the development of AOTFs with significantly expanded FOV.

Temperature Effects in an Acousto-Optic Modulator of Terahertz Radiation Based on Liquefied SF6 Gas

The acousto-optic (AO) diffraction of terahertz (THz) radiation in liquefied sulfur hexafluoride (SF6) was investigated in various temperature regimes. It was found that with the increase in the temperature from +10 to +23 °C, the efficiency of the AO diffraction became one order higher at the same amplitude of the driving electrical signal. At the same time, the efficiency of the AO diffraction per 1 W of the sound power as well as the angular bandwidth of the efficient AO interaction were temperature independent within the measurement error. Increase of the resonant sound frequency with decreasing temperature and strong narrowing of the sound frequency bandwidth of the efficient AO interaction were detected.