High resolution near IR spectrometer for the diffuse interstellar medium

We have developed a pressure scanning cold Fabry-Perot spectrometer for the study of the warm diffuse component of the interstellar medium. In order to reduce thermal background and increase sensitivity optical components are cooled to 77K in a LN_2 cryostat. Wavelength scanning is accomplished by changing N_2 pressure in the etalon chamber. The instrument can be scanned over its free spectral range of 300km;s(-1) , and it has a velocity resolution of 20km;s(-1) . A high performance InSb photodiode is used with an integrating preamplifier. This instrument, with its high spectral resolution and large field of view (~ 1(o) ) is well suited for observation of line emission from extended low surface brightness objects. Its design has been developed to allow detection of the diffuse Brackett-gamma and Brackett-alpha emission lines from the warm ionized component of the ISM.