Infrared absorption measurement using the photothermal deflection effect of thallium bromide iodide (KRS-5): Examination of basic characteristics

Abstract

An infrared absorption measurement technique based on the photothermal deflection effect of thallium bromide iodide (KRS-5) is proposed. The optical system for infrared absorption measurement by this technique consists of a crystal block of KRS-5, an XY axis translation stage, an off-axis parabolic reflector, a He–Ne laser, and a position sensitive detector. To estimate the sensitivity of the system, its typical frequency characteristics and the thermal diffusion length of a block of KRS-5 were measured. The thermal diffusion length was measured over the chopping frequency range of 5–15 Hz. The accuracy of the measured thermal diffusion length was compared with that theoretically calculated using the physical constants of the thermal conductivity, density, and specific heat. The measured results agreed well with those calculated theoretically within ±4 μm. We also analyzed the frequency characteristics for a carbon black sample and estimated the detection limit of absorption that is characteristic for some irradiance levels at the sample surface. The results suggested that our proposed technique is useful for infrared absorption measurement.