Alignment-Free Laser And Higher-Order Laguerre-Gaussian Laser Using Cat-Eye Retroreflectors

The distributed laser with cat-eye retroreflectors has an alignment-free property,which means that the laser’s output power can be kept stable without adjusting other resonant parameters within a specific working distance and field of view.In this paper,we theoretically investigated the method of selecting the optimal operating point and optimizing the device parameters.We demonstrated a continuous-wave end-pumped Nd:YVO₄ alignment-free laser with cat-eye retroreflectors by optimizing the working distance and field of view of the laser without adjusting other parameters by calculating and analyzing the stability zones of the resonator,spherical aberration,and field curvature.The detailed works are as follows.1、We discovered that the cat-eye defocus caused by the spherical aberration of the intracavity lens is the main factor limiting the laser’s alignment-free working distance by calculating the stability zone of the resonator.By correcting the lens’s spherical aberration to create an alignment-free laser,we achieve a laser output of 5.9W at a working distance of 5 m.Besides,we analyzed and optimized the resonator working point using cavity mode theory to achieve an alignment-free working distance of 1-5 m.Without adjusting other devices in the cavity,the alignment-free laser output power was more than 5.7 W over a working distance of 1-5 m.2、We investigated the effect of the intracavity lens’s field curvature on the laser’s output characteristics and discovered that the cat-eye defocus introduced by the field curvature introduces losses to the resonant cavity,limiting the alignment-free field of view of the resonator.We designed two field curvature compensated cat-eye retroreflectors to build an alignment-free laser and achieved an alignment-free field of view of±20°at 5 m working distance.Without changing other devices in the cavity,the alignment-free laser output power was more than 4.2 W at a working distance of 5 m and a field of view of 0-±20°,with a less than 9%output power fluctuation.3、Inspired by the effect of cat-eye defocus on the retroreflective effect,we propose a method to select the single Laguerre-Gaussian（LG）mode using the intracavity spherical aberration.By designing and building a LG mode laser based on the cat-eye retroreflector,we achieved the selected output of a single LG mode with radial index p=0 and angular index m from±10 to±33.