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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.

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Consider a Cerenkov laser, using for the slow‐wave structure a dielectric waveguide whose substrate consists in a nonlinear dielectric presenting the self‐focusing effect. The characteristics of the Cerenkov laser specified in the foregoing are investigated theoretically for the two‐dimensional model which takes into account the field distribution in the transverse direction. First, the dispersion relations are considered for the electromagnetic wave modes (TM waves) propagated along a two‐dimensional nonlinear dielectric waveguide. Then the dispersion relations are discussed for the coupled electromagnetic fields in the Cerenkov laser using the nonlinear dielectric waveguide. Finally, the spatial growth rate of the growing wave obtained from the dispersion relation for the coupled fields derived in the foregoing is investigated numerically in detail. From the forementioned discussion, it is found that the spatial growth rate for the Cerenkov laser treated in this paper is improved compared to the Cerenkov laser for which the slow‐wave structure is composed of linear dielectrics only.