Abstract
We report direct measurements of the tunable spin-flip Raman (SFR) laser linewidth, obtained by heterodyning the SFR laser output with the output from a cw gas laser. The measured linewidth for the cw SFR laser operating near 5.3 μm is < 1 kHz and is limited by the spectrum analyzer resolution. The measured linewidth of < 1 kHz is the narrowest known for any tunable source of coherent radiation in the infrared.