INFRARED-ABSORPTION MEASUREMENT USING THE PHOTOTHERMAL DEFLECTION EFFECT OF THALLIUM BROMIDE IODIDE KRS-5 - EXAMINATION OF BASIC CHARACTERISTICS

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 freq uency characteristics and the thermal diffusion length of a block of K RS-5 were measured. The thermal diffusion length was measured over the chopping frequency range of 5-15 Hz. The accuracy of the measured the rmal 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 mm. We also analyzed the frequency characte ristics for a carbon black sample and estimated the detection limit of absorption that is characteristic for some irradiance levels at the s ample surface. The results suggested that our proposed technique is us eful for infrared absorption measurement. (C) 1998 American Institute of Physics. [S0034-6748(98)05011-4].