Off-axis pumped Tm:YLF vortex laser with continuously tunable wavelength

Abstract

In this paper, HG mode conversion and etalon are used to achieve a 1.9 μm vortex beam output in a Tm:YLF laser while achieving a certain range of wavelength continuous tuning. In theory, the wavelength tuning characteristic and tuning capability of the etalon are analyzed. In the experiment, the HG1,0 mode laser is achieved by off-axis pump, and the optical field distribution and beam quality are relatively consistent with the theoretical state. After the HG1,0 mode laser passes through the π/2 mode converter, the LG1,0 vortex beam output is realized. The optical field distribution and beam quality of the vortex beam are relatively close to the theoretical state. The threshold of the laser at LG1,0 mode is 3.2 W, the slope efficiency is 37.7%, the optical–optical conversion efficiency is 34%, and a laser output of 8.6 W is obtained at the highest pump power of 25.3 W. On this basis, the continuous wavelength tuning of the LG1,0 mode vortex beam from 1937 nm to 1921 nm was achieved by rotating the etalon. Through comparison, it can be found that the optical field distribution and output power of each wavelength are relatively close during the wavelength tuning process. Finally, the topological charge of the vortex beam is measured by the interference of the vortex beam with the spherical wave and the plane wave. This article is of great significance for the further research of multi-dimensional tuning to realize large-capacity optical communication.