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.

Single crystal growth and effect of cleavage micro-striations on the crystallinity and optical properties of mercurous halide single crystals

“…Polarizing and acousto-optic (AO) devices are widely used as important components of optical switches, modulators, and filters in modern optical technology. [1][2][3] Generally, the materials for fabricating these devices require large birefringence to split ordinary light with extraordinary light in a wide transparent range. Commercial polarizing materials, including α-BBO (0.19-3.5 μm), YVO 4 (0.5-4.0 μm), and CaCO 3 crystals (0.35-2.3 μm), are generally applied in ultraviolet-visible-near infrared bands.…”

Growth and Temperature-Dependent Mechanical and Thermal Properties of One-Dimensional Chain Structure Hg2Br2 Crystals for Infrared Acousto-Optic Device Application

“…Acousto-optic tunable filters (AOTFs), which detect object by the characteristic spectral signatures of different materials, have drawn much attention in a variety of fields, such as space exploration, medical diagnostics, atmospheric environment monitoring, and detection of military camouflage targets and harmful biological agents. , The AOTF has superior advantages of accessing the wavelength randomly and operating in several spectral bands simultaneously . Besides the improvement in target recognition in a complex spectral environment, the AOTF also features the processing of data in real time, easy integration into the optical system, and fast response time. , At present, the AOTF operated in the ultraviolet–visible to mid-wave infrared (UV + NIR + SWIR + MWIR, from 400 nm to 5 μm) is relatively mature commercially, while the AOTF applied in the long-wave infrared (LWIR, from 8 to 14 μm) has not been well developed. , …”

“…The Hg 2 Br 2 crystal has excellent acousto-optic properties, the M 2 value (2600 × 1.5 × 10 –18 s 3 /g) of which is about 2.5 times that of the Hg 2 Cl 2 crystal, and it has a wide transmission range (0.4–30 μm) . Moreover, the Hg 2 Br 2 crystal has a low acoustic velocity and attenuation coefficient, and the AOTF based on the Hg 2 Br 2 crystal has large separation and acceptance angle owing to the large birefringence of crystals. ,,, …”

“…4,5 At present, the AOTF operated in the ultraviolet−visible to mid-wave infrared (UV + NIR + SWIR + MWIR, from 400 nm to 5 μm) is relatively mature commercially, while the AOTF applied in the long-wave infrared (LWIR, from 8 to 14 μm) has not been well developed. 6,7 The intrinsic properties of acousto-optic crystals determine the wavelength regions of AOTFs. Till now, PbBr 2 , Tl 3 SeAs 3 , and Hg 2 X 2 (X = Cl, Br, and I) crystals are regarded as promising candidates in LWIR.…”

“…12 and acceptance angle owing to the large birefringence of crystals. 6,8,13,14 Up to now, some research studies have been carried out on Hg 2 Br 2 crystal growth, property characterization, and device fabrication. As early as 1970's, Barta et mainly reported the growth of mercurous halide family crystals and the design and fabrication of acousto-optic devices.…”