Hideyuki Minato

Remote refractive index difference meter for salinity sensor

A remote refractive index difference meter was designed and tested for use as a salinity sensor. the principle is to measure the difference between the real seawaters index and the standard seawaters. The meter is composed of a semiconductor laser, a partitioned water cell, and a solid position detector. The performance of the sensor is also described. >

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.

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 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.