Angular-Spectral Characteristics of Acousto-Optic Tunable Filters Based on Mercurous Halide Crystals

Abstract

The angular and spectral properties crucial for the functionality of acousto-optic (AO) devices are determined by phase-matching geometries in AO interactions. In applications such as spectral imagers based on acousto-optic tunable filters (AOTFs), systematic throughput is constrained by the angle separating diffracted and transmitted light. This research introduces an analytical model that elucidates the angular-spectral properties of diffracted beams in mercurous halide crystals. These crystals possess a wide transmissive spectral range, from visible light to long-wave infrared light. The study computes and confirms correlations between the separation angle and parameters including incident angle, polarization, acoustic angle, and crystal birefringence. Experimental validation conducted on mercurous halide and tellurium dioxide crystals demonstrates that higher birefringence in crystals significantly amplifies the separation angle, augmenting the device’s performance. The study contributes to the development of devices with large separation angles during the design phase, enhancing systematic throughput in spectral imaging applications.

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

“…For a specific acoustic angle and a specific light wavelength, only one or two phasematching combinations satisfy PTP, as shown in Figure 2a. Since the separation angle of the phase-matching combination with a larger incident angle (dashed line) is smaller [29], and an incidence angle close to 90 • would complicate the manufacturing of the device, the smaller incident angle and its corresponding acoustic angle (solid line) are selected as the optical cut angle for the incident surface and the acoustic cut angle for the transducer surface of the AO crystal.…”