Line narrowing of polycrystalline Cr:ZnS/Se laser oscillation due to suppression of spatial hole burning in non-selective twisted mode cavities

Current work reports on comparative laser characterization of Cr:ZnS/Se polycrystalline gain media in non-selective linear polarized and twisted mode cavities. The work aimed to identify the mechanism of the spectral broadening of continuous-wave Cr:ZnS/ZnSe lasers in the non-selective cavity. Randomly polarized Er-fiber laser operating at 1567 nm with 10W maximum power utilized as a pumping source. By adjusting the orientation of intracavity waveplates with respect to intracavity polarizer, the switching between linear polarized and twisted cavity mode was realized. We demonstrated that in the presence of a spatial hole burning effect in the gain element, the spectral output of the Cr:ZnS/Se lasers in non-selective cavities is broadened to ~20-50 nm. It was shown that suppression of the spatial hole burning in the gain element could be realized by enabling circular polarization of the laser radiation in the gain element in the so-called "twisted mode" cavity. In this cavity, narrow-line oscillations with linewidth limited by wavemeter resolution (~90 pm) were demonstrated using the same laser crystals without any selective elements.