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Abstracf-The basic differential equation governinglaser noise is derived from classical and quantum mechanical considerations. Its linearized Van Der Pol form is used to derive the frequency, field, and intensity fluctuation spectra.

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This paper describes the design, construction, and testing of a probe for the measurement of electric current in a circuit. This measurement is performed by using Faraday rotation produced in a beam of polarized light that encircles the current~carrying conductor. Such a probe is an absolute instrument whose calibration only depends upon the Verdet constant of the rotative medium and is independent of the dimensions Of positions of the light path relative to the current. The time resolution of the probe is the optical transit time about the closed path and can in practice be reduced to a few nanoseconds.

The absorption of solar radiation and the emission from the atmosphere (effective sky temperature) were measured over the ranges of the millimeter region corresponding to rotational lines of ozone centered at 30,056, 36,025, and 37,830 Mhz. The measurements were made possible by the special development of a frequency-switching radiometer and a gain-compensation technique. The contributions of ozone to atmospheric absorption and emission are evaluated from the solution of the radiative transfer equation on the basis of a line-width function of temperature and pressure and the ARDC 1959 standard atmosphere; the contributions of the water vapor and the oxygen are determined from the theories of Barrett and Chung for H•.O and Meeks for O•. The intensity of the 37,830-Mhz line calculated by Gora was verified in a laboratory study. The width of this line was also found to coincide with the 2340-Mhz value at standard atmospheric conditions as derived by Walshaw from the 9.6-• ozone band. Emission by the 30,056-Mhz line and absorption of the solar radiation by the 37,830-Mhz line were detected, with the line strengths in reasonable agreement with the model calculation. 6137