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The optical properties of single crystals of tellurium (Te) are investigated in order to develop acousto-optic (AO) devices operating in the longwave infrared spectral region. The optical transparency of carefully cut and polished plates and large size samples of Te crystals was measured from 4 to 24 µm. The absorption of ordinary and extraordinary polarized optical beams was measured along various directions in the crystal with respect to the optic axis. Using a 10.6 µm CO2 laser the absorption coefficient for the best samples of Te was found to be 0.07 cm − 1 for the ordinary and between 0.07 and 4.0 cm − 1 for the extraordinary polarized optical beam. Here, we also discuss the possible application of Te crystals in fabricating AO imaging filters.

The acoustic, optic and acousto-optic properties of tellurium crystals have been examined in order to develop an acousto-optic tunable filter (AOTF) operating in the long-wave infrared (LWIR) region. The AOTF design is based on the wide-angle regime of light diffraction in the YZ plane of the birefringent crystal operating from 8.4 to 13.6 µm. Device characteristics were obtained from both theoretical and experimental investigations. Experiments were carried out using both a 10.6 µm pulsed CO2 laser as well as a tunable CO2 laser operating in a continuous wave mode from 9.2 to 10.7 µm. The AOTF was tuned over the acoustic frequency range of 81.5–94.7 MHz. The filtering performance in the tellurium device was provided by a pure shear elastic wave propagating at a 95.8° angle with respect to the positive direction of the optic axis, while an ordinary polarized optical beam was incident at the Bragg angle of 6.0° relative to the acoustic wavefront. At 10.6 µm, the measured spectral bandwidth of the filter was 127 nm and the optical transmission coefficient was around 8.8% with 2.0 W drive power. This paper presents detailed results from both the theoretical as well as experimental device characterization including the spectral images obtained with a 256 × 256 mercury cadmium telluride camera cooled to 77 K.

We examined the physical properties of infrared optical glasses composed of tellurium, germanium, selenium, sulfur and silicon. In particular, we measured optical, acoustic and photoelastic parameters of the following alloy compounds: germanium–selenium–tellurium (Ge–Se–Te), germanium–selenium–sulfur–tellurium (Ge–Se–S–Te), germanium–silicon–tellurium (Ge–Si–Te) and silicon–tellurium (Si–Te). Like single-crystal tellurium, the glasses demonstrate good acousto-optic (AO) diffraction efficiency and have reasonable optical transparency in a wide spectral region covering wavelengths from 1.5 to 20 μm. The optical, acoustic and photoelastic properties of the tellurium-based compounds were measured using infrared lamp sources of radiation as well as He–Ne and CO2 lasers. In this paper, we report on the optical, acoustic and photoelastic parameters of a selection of these compounds and discuss the advantages and disadvantages of using these glasses for AO device applications. We also present the measured characteristics of an AO cell fabricated in a Si20Te80 glass material which exhibited high optical uniformity and long-term chemical stability.

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