Fluorescent radiation thermometry at cryogenic temperatures based on detailed balance relation

We demonstrated a new method of radiation thermometry at cryogenic temperatures on the basis of the detailed balance relation between absorption and photoluminescence in a small n-type-modulation-doped GaAs quantum-well sample. This method has unique advantages such as being non invasive. It also does not need to be calibrated and possibly offers high spatial resolution. We measured temperatures of a sample mounted on a sapphire substrate attached to a copper cold finger at 7-101 K in a cryostat. The temperatures measured with this method were consistent with those obtained from a separate calibrated traditional temperature sensor. The estimated uncertainties were ±2 K below 50 K and ±8 K below 100 K.