Periodically tunable continuous-wave intracavity diamond Raman laser via birefringent filter

We report a periodically tunable continuous-wave intracavity diamond Raman laser employing a rotating quartz birefringent filter (BRF). Experimental results reveal a counter-intuitive phenomenon where the insertion of a lossy BRF leads to higher Stokes output power compared to the free-running regime. This power enhancement is primarily attributed to the significant spectral narrowing of the fundamental field, which increases the effective Raman gain and overcompensates for the additional insertion losses. By utilizing BRFs with thicknesses of 0.5 and 1 mm, the system achieved stable tuning ranges of approximately 0.24 and 0.3 nm, respectively, with maximum Stokes output powers of 1.24 and 1.05 W. It should be noted that although the absolute wavelength span observed at extreme BRF rotation angles can extend to 2.06 and 1.77 nm, respectively, this is primarily due to intermittent outliers. Both the output wavelength and power exhibit a strict 180° periodicity relative to the BRF rotation angle.