A 4x1 GHz array acousto-optical spectrometer

In this paper an array acousto-optical spectrometer (AOS) with four 1 GHz bands and a frequency channel spacing of 1 MHz is presented. A discussion about the requirements which have to be fulfilled by the presented instrument for applications in radio astronomy is given as well as e detailed description of the optical design. Remarkable test results have been achieved such as an Allan-Variance minimum time of about 1000 s, identical noise performance, and identical frequency calibration of all bands. The reproducibility of measurements has been demonstrated by tests with CH3CN, using an absorption cell. The question of the maximum number of bands per array AOS is discussed. Although it may seem promising to increase the number of bands per optical unit to e.g. eight or more instead of four, a strong limitation has been found due to the increasing r.f. power level on the Bragg cell which affects the baselines of the spectra.