Comparative Analysis of the Effect of Gradient Index Lens and Brewster Plate on the Stability of Z-shaped Optical Resonator

Abstract

This thesis presents the comparative analysis of a Z-shaped optical resonator having four mirror laser cavity, with two flat feedback end mirrors and two curved mirrors at the two ends of the Brewster and Gradient index lens using Ray Transfer Matrix by considering the effect of both Gradient Index lens and Brewster plate. The resonator components and their Ray Transfer matrix have been defined and the effect of each component with corresponds to its value have been examined in order to identify whether or not the component has an effect on the stability of the system. It is recognized that the stability and output beam of the two folded mirrors of Z- folded cavity do not depend on the position of the Brewster plate and Gradient index lens. The responses of the stability region and beam spot size with the variation of the cavity components such as length between mirrors, radius of curvature, refractive index and folding angle have examined in comparative form for both Gradient Index lens and Brewster based models. The total cavity length of 91 mm with pulse repetition rate of 3.84349 GHz for Brewster plate-based and total cavity length of 78 mm with pulse repetition rate of 3.29442 MHz for Gradient Index lens based is matched to cover round trip distance of 874225000 mm in the cavity for both models. The minimum beam waist is found in the sagittal plane for both models at the reflecting surface of the second spherical mirror with tangential (wt) = 58.5962 and sagittal (ws) = 55.8025 and minimum wave front curvature with tangential (wt) = 58.597 and sagittal (ws) = 55.8034. It is found that Gradient index lens is applicable for output beam magnification and Brewster plate is used for avoiding the astigmatism effect for propagation of laser beams.