Yoshinari Ishido

Development of a five-band multi-spectral infrared radiometer for low temperature measurements

A five-band infrared radiometer has been developed for the measurement of spectral radiance and radiance temperature at low temperatures. The optical system of this radiometer consists of a scanning plane reflecting mirror, five narrow-band interference filters in the 6–12 μm band, a mirror-type rotating chopper, a cold source, a hot source, and a HgCdTe semiconductor detector. Measurement of radiance temperature and spectral radiance using this radiometer is carried out automatically using a personal computer. The calibration of the output signal for each spectral channel of the radiometer is carried out exactly using a blackbody source with an accurate temperature controller. The short-time stability of the radiometer is estimated to be within 0.2% mean deviation for the main spectral channel. The temperature detection sensitivity of a radiometer is evaluated as the noise equivalent temperature difference (NETD) for the optical and measuring system; the NETD for the main spectral channel is estimated to be about <0.2 °C. The minimum detectable radiance for the main spectral channel is also estimated to be about <0.002 mW/cm2 sr μm. For confirmation of the long-time stability of the radiometer, the measurement of the radiometer output ratio between the blackbody source at a temperature of 15 °C and the hot source at a constant temperature of 40 °C is carried out over 3 h; the long-time stability of measurement for the main spectral channel is estimated to be within ±0.3 °C mean deviation. The variation over time of the spectral radiance and the radiance temperature of the cloud in the sky was actually measured using the radiometer, and its usefulness was clarified.

Development of an infrared absorption measurement method using the photothermal deflection effect of thallium bromide iodide (KRS-5): Measurement with a stepped-scan Fourier transform infrared spectrometer

An optical system was produced experimentally for infrared absorption measurements based on the photothermal deflection effect of solid material (KRS-5), which does not require a cell for the medium as does absorption measurement using the photothermal deflection effect of liquids. In this study, it was shown that the photoelastic effect of photothermal beam deflection exists in KRS-5 crystals, and the necessity of regulating the polarization direction of the laser beam is described. Infrared absorption spectral measurements were done on several samples using a stepped-scan Fourier transform infrared spectrometer for the evaluation of this technique. The results agreed well with the results of transmittance measurements of the same samples. In conclusion, this new technique seems to be useful for the measurement of infrared absorption.