Cavity Enhanced Raman Heterodyne Spectroscopy in Er3+: Y2SiO5 for Microwave to Optical Signal Conversion

The efficiency of the frequency conversion process at the heart of Raman heterodyne spectroscopy was improved by nearly four orders of magnitude by resonant enhancement of both the pump and signal optical fields. Our results using an erbium doped Y
₂
SiO
₅
crystal at temperatures near 4 K suggest that such an approach is promising for the quantum conversion of microwave to optical photons.