Acousto-optic interaction model with mercury halides (Hg2Cl2 and Hg2Br2) as AOTF cristals

Abstract

Acousto-optic tunable filters (AOTF) are used in the development of hyperspectral imagers from the ultra violet (UV) to the long wave infrared (LWIR). They have the advantage to be an all-solid-state and robust device with no-moving parts that can fast tune their filtered frequency carrier. Such a device is developed by bonding a piezoelectric transducer on a specially cut birefringent crystal. In the LWIR there is a global investigation on efficient solutions for AOTF in future spectral filtering applications. Crystal of mercurous chloride (Hg2Cl2) and mercurous bromide (Hg2Br2) are candidates that demonstrate an advantage in this spectral domain, thanks to a broadband transparency and a fairly large value of their figure of merit M2. Industrial development of those crystals has recently started and presents an excellent opportunity to prospect feasibility of such AOTF development. The purpose of our work is to develop a numerical tool to have a better understanding of the acousto-optic interaction inside mercurous halides crystals. Unfortunately, all the characteristics of those mercurous halides based crystals are not well known nowadays. One important component of the photoelastic tensor is always missing. It implies that the unique interaction configuration that optimizes the diffraction efficiency for a wavelength range can’t be computed analytically with the usual techniques. To overcome this difficulty, we propose a numerical tool based on an acousto-optic interaction and an acoustic wave propagation models. We will also include the AOTF considerations and the theoretical background needed to carry out the filter design.