Response characteristics of a very low level DC current amplifier which has a very high feedback resistor (1010Ω) are studied numerically and experimentally from the viewpoint of high speed response. In experiments, a positive feedback circuit is proposed and examined to improve the transient response of the amplifier. As a result, the rise time of 30 μs at 20 pA ofthe current sesitivity was obtained, by using the positive feedback circuit. It is verified that, by adapting the positive feedback circuit without causing internal oscillation, the response time of the DC amplifier is substantially improved from one half to one eighth as compared with former methods, if the shielding of feedback circuit is good enough and the very high and pure feedback resistorsare available.
The present paper describes the results of observation on the behaviour of a sectional snow cloud at Yonezawa by a Mie scattering laser radar. Laserradar offers the measurement of the phase of a cloud to a certain extent by using the depolarization property of backward scattering light. The present laser radar has two receiving channels for measuring vertically and horizontally polarized signals simultaneously. During the observation there was once a heavy snow fall which continued until the following day, besides several intermittent snow falls. From the observation of continuous snow, the most significant behavior of the cloud before the snow fall was that the ceiling height decreased gradually, after the ice-crystal cloud of the upper layer had changed to snow-flake cloud. For intermittent snow, the variation in the height of the clouds was much more prominent than in the case of continuous snow.
Crystal orientation was studied for films of microcrystalline SiGe alloys (μc-SixGe1-x) prepared at low substrate temperatures by RF sputtering of Ge target in SiH4 gas diluted with H2. The composition x of SixGe1-x alloy was controlled either by changing the substrate temperature Ts or the flow rates [SiH4/(SiH4+H2)]. It was found from X-ray diffraction measurements that the (220) orientation increased remarkably at substrate temperatures above 300-350°C. The maximum ratio of (220) peak height to (111) peak height increased to nearly 90 at the substrate temperature of 420°C. The (220) orientation was most notable when the composition was nearly 0.5.
The characteristics of stored ions in the RF quadrupole trap are measured by the RF resonance absorption method. The number of stored ions and the collision time are measured by fitting the observed absorption signals to the theoretical ones under the state of continuous ion creation. In the storage time measurement, the reduction of absorption signals after ion creation is observed by sweeping the oscillation frequency of stored ions. Since the transient ringing phenomenon appears in these observed signals when the sweep rate is high, the condition of appearance of this phenomenon and the relation between the number of ions and the maximum signal amplitude are analyzed. On the basis of these analyses, the storage time of Xe+ ions is determined to be about 20 seconds.
The optimization of the high spectral resolution lidar which uses anatomic vapor filter for remote measurement of atmospheric temperature is discussed. The procedure for selecting the most suitable atom to use as the filter is shown, and the optimum filter temperature at which to measure atmospheric temperature with the highest sensitivity is determined. It is shown that it is best to use Cs at 550K for a 5cm cell length. Error analysis indicates that the fluctuation of filter temperature is critical for accurate measurement and it was found that the fluctuation of the filter temperature must be within 0.3K for an error ±1K in atmospheric temperature. It was found that it takes only 14s to measure atmospheric tem-perature at the height of 5km with a 30m range resolution by using laser pulses with 20mJ/pulse and 25 pps, and a 35cm dia. telescope.