Polarization Characteristics of Raman Scattering in KGW Raman Laser Crystals by Polarized Incident Light

Potassium gadolinium tungstate (KGW) crystals are prospective Raman gain media in the development of solid-state Raman lasers. Especially, the
$N_{p}$
-cut KGW crystal with the maximum Raman gain for the Raman shifts of 768 cm
⁻¹
and 901 cm
⁻¹
are of great importance for generating laser sources, such as watt-level continuous-wave and nanosecond pulsed KGW Raman lasers in spectral range from UV to IR [1]–[4]. The polarization of the Stokes waves in the above laser source is parallel to that of the fundamental waves, either aligned with the
$N_{g}$
axis of KGW crystals corresponding to the Raman shift of 768 cm
⁻¹
, or with the
$N_{m}$
axis corresponding to the Raman shift of 901 cm
⁻¹
. In particular, it has been demonstrated that the Stokes waves based on the Raman shift of 901 cm
⁻¹
with the polarization along the
$N_{g}$
axis can be generated in the orthogonally polarized dual-wavelength laser [5]. Therefore, the polarization of Stokes waves is not unique to a Raman shift of the KGW crystal, which is related to the polarization of fundamental waves. To the best of our knowledge, there is no report on the relationship between the fundamental and Stokes wave polarizations in KGW Raman lasers, that is, the incident light and Raman scattering polarizations in KGW crystals.