Abstract
A spectrometer with different cells for photo-acoustic or thermal detection of optical absorption at liquid helium temperature is described. Three types of detectors can be used: a microphone a carbon-glass thermometer or the (semiconducting) sample itself. The first tests are made in the near-infrared range on III-V materials doped with chromium (GaP) and vanadium (GaAs, GaP and InP). They demonstrate the high sensitivity of the thermometer.