Single-prism polarizer for laser emission with higher power

Давыдов Б.Л. Монопризменный поляризатор для лазерного излучения повышенной мощности // Оптический журнал. 2022. Т. 89. № 6. С. 33–42. http://doi.org/10.17586/1023-5086-2022-89-06-33-42

Davydov B.L. Single-prism polarizer for laser emission with higher power [in Russian] // Opticheskii Zhurnal. 2022. V. 89. № 6. P. 33–42. http://doi.org/ 10.17586/1023-5086-2022-89-06-33-42

B. L. Davydov, "Single-prism polarizer for laser emission with higher power," Journal of Optical Technology. 89(6), 332-338 (2022). https://doi.org/10.1364/JOT.89.000332

Subject of study. The properties of a new prismatic polarizer-analyzer of laser (optical) emission with higher power were investigated. The polarizer was designed based on a birefringent crystal in the form of a single total internal reflection prism with a triangular cross-section. Spectral dependences of the geometry of the cross-section in the refraction plane were investigated for two selected polarizer materials. Aim. The study was aimed at designing a polarizer in the form of an individual single-element device capable of functioning in the laser beams with higher power that maintains the original direction of radiation propagation with minimum optical losses and without anamorphosis of the beam cross-section. Method. The transmission of radiation through an optically anisotropic crystalline prism with an arbitrary triangular cross-section was investigated using mathematical modeling. Snell’s equations, which were developed for refraction and total internal reflection of radiation on the faces of an anisotropic prism, were used. Based on the obtained solutions, the spectral dependences of angular structural parameters of prismatic polarizers were calculated under conditions of maintaining the collinearity of the input and output rays and their refractions on the input and output faces fixed at Brewster’s angles. The energy losses and spectral ranges of operation of prismatic polarizers composed of two selected crystalline materials with a priori defined geometry were analyzed. Main results. A new prismatic polarizer was designed and investigated. Its main feature corresponds to anisotropic total internal reflection of optical radiation from one of the faces of a birefringent single prism under Brewster’s refractions on the input and output faces. We established that the device exhibits minimum optical losses, collinearity (or coaxiality) of unpolarized and polarized beams, and no anamorphotic distortion of the cross-section of the output p-polarized beam. Furthermore, we demonstrated that in the case of virtually symmetric prisms for which the difference between the structural angles and Brewster’s angles is 3°–7°, the effect of anamorphism of the beam cross-section is negligibly small. The spectral ranges of the device operation were determined for several specific designs. A weak dependence of spectral bands on the selected orientations of the polarizer crystal was observed. It manifests in the symmetry of the obtained dependences. We demonstrated that the prisms composed of YVO₄ crystals are the most advantageous for obtaining the widest spectral bands in the near- and mid-infrared spectral ranges. Angular tolerances for the divergence of the incident beams were determined based on analysis of the angular deviations of the incidence angles from the Brewster’s angles. The device can also be used in observational optics as an anisotropic equivalent of the isotropic Dove prism. The difference between the proposed device and the Dove prism is the fact that the proposed device provides the potential of observing an image in ideally linearly polarized light. Practical significance. The proposed single-element design of a prismatic polarizer with Brewster’s input and output faces enables the use of the device for polarization (or polarization analysis) of laser beams with power higher than the values for which the standard multicomponent polarizers are applicable.