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Measurements of the Spectral Response of the MPIfR Bolometers

An important property of a bolometer receiver is its spectral response. Knowing this function and the atmospheric transmission, the effective observing frequency for radio sources of given emissivity index can be calculated (see NIC-manual 1.4-07, Appendix C, ``Effective observing frequency''). Furthermore this information is essential in order to estimate the line contribution to the bolometer signal.

The spectral response of a bolometer receiver is a function of many parameters. Unfortunately some of them are difficult to determine and a direct measurement of the complete bolometer system is very desirable.

This can be done by using the receiver to take a spectrum of a source of known emissivity (a black body) with a spectrometer of known efficiency (a Martin-Puplett-interferometer). The spectral response is then obtained by dividing the measured spectrum by the source spectrum and the spectrometer's efficiency curve. A relative spectral calibration of this kind is usually done before a new bolometer system is shipped to the telescope.


  
Figure 1: MAMBO central channel spectral sensitivity
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Figure 1 shows the spectral sensitivity of the central channel of the 37 element 1.2 mm bolometer array used during the observing campaign in winter 98/99 (''MAMBO I''). The variation of the shape of the spectral sensitivities of the different channels is typically below 5% so that this curve gives a good estimate for all channels of this bolometer array. According to ongoing improvements of the bolometers the spectral response of a receiver depends on the year. A compilation of spectral responses of the MPIfR bolometer systems used at the 30 m MRT and the 10 m HHT can be found under:
http://www.mpifr-bonn.mpg.de/div/bolometer/spectra/
spectralresponse.html



J. GROMKE and E. KREYSA, MPIfR Bonn, Germany


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Next: Call for Observing Proposals Up: IRAM Newsletter 45 (August 2000) Previous: News from the 30m
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