Coherent population trapping resonances in cesium vapor can be used to determine DC flux densities in the range from 1 µT to 1 mT with typically 3•10 −5 relative uncertainty. For fields modulated at a few kHz, we find sensitivities of below 10 pT within 0.5 s integration time. From the signal-to-noise ratio the sensitivity can be extrapolated to 500 fT/ √ Hz. A quantitative understanding of the lineshape allows to detect DC fields of several nT even when the Zeeman components of the resonance are not resolved.

No abstract

No abstract

No abstract

The results are given of observation of solar radio emission of the S-component at 8.15 ram-2 and 2.25 ram-2 made with the 22 m radio telescope of the Crimean Astrophysical Observatory. Solar radio images are obtained at both wavelengths. The data are presented of radio emission intensity and brightness temperatures of 10 sources of the S-component as well as the result of a flare observed. The sources of the S-component appear to be opaque at millimetre wavelengths.From the observations of sources of a slowly varying component of solar radio emission (S-component) at millimetre wavelengths one may obtain information about the located layers of the active regions on the sun which the sources are associated with as a rule.The investigation at 8 ram-2 shows that excess in brightness temperatures of sources, as compared to the level of the quiet sun, attains (2.5-6) x 103 K, their sizes ranging from 1'-2' up to 4'-5'. Radio emission is of a thermal character and the sources are optically thin at this wavelength (Salomonovich, 1962; Khangil'din, 1964).Observations of two sources of S-component carried out simultaneously at 8 mm-2 and 4 mm-2 have also showed that they are optically thin at these wavelengths and have a thermal character of radio emission (Kislyakov and Salomonovich, 1963). Tsuchiya and Takahashi (1968) came to the same conclusion, observing the sources of S-component at 8.5 ram, 4.3 mm and 3.2 mm wavelengths. They note, besides, that the spectrum of S-component (the dependence of radio emission flux density upon the wavelength) becomes flat at millimetre wavelengths, beginning from 8.5 ram-2 and shorter. In the paper by Apushkinskii and Tsiganov (1967) the brightness temperatures of S-component sources, identified with ftocculi, are found to be greater at 4 ram-2 than at 8 ram-2. At the shorter millimetre wavelengths, as far as we know, the sources of S-component were not observed.In September-October 1967 the observations of the solar radio emission were made simultaneously at 2.25 mm and 8.15 ram* by the 22 m radio telescope of the Crimean Astrophysical Observatory of AS USSR in order to investigate the sources of S-component at the shorter wavelengths and to determine the spectrum of the solar radio emission. It was necessary to obtain the solar image, scanning it by the pencil * Instrumentation used at 2.25 ram-2 was developed at NIRFI.