Large-dynamic-range Alignment-free Laser And Higher-order Optical Vortex Beams Based On Cat-eye Retroreflectors

The alignment-free lasers refer to the lasers with their cavities consisting of retroreflecting optics,which therefore benefit large misalignment tolerance and have important applications in defense,sensing,communication as well as energy transfer.This thesis focuses on the distributed-cavity large-range alignment-free laser for adaptive wireless laser energy transfer application.By optimizing the cavity design and optical design,the end-pumped solid-state laser with its cavity incorporating cat-eye retroreflectors（CERs）was capable of operating efficiently over a large dynamic range.A new method to obtain high-order Laguerre-Gaussian（LG）mode optical vortex by mode-selection via spherical aberration of a defocused CER in the laser cavity was also proposed and experimental investigated.The main contents are as following:1.The theoretical model and basics of the alignment-free laser based on CER cavity was discussed.The optimal parameters of the lens focal length,mirror radius of curvature and distances between the components were determined based on the ABCD matrix of the cavity and object-image relationship of the optical system.The optimal pump size,laser crystal and the mirror reflectivities of the coupled cavity were determined based on laser cavity theory and rate equation,as well as experimental results.2.The working distance of the distributed-cavity laser was optimized.We found that the CER defocusing induced by the spherical aberration of the lenses and the narrow cavity stability zone at long working distance were the main issues which limited the working distance of the laser.With the spherical aberration corrected by using an aspheric lens,the Nd:Gd VO₄ laser at 1063 nm could deliver 5.82 W continuous-wave output under an incident laser diode pump power of 16.6 W at a long working distance of 5 m,which was improved significantly compared with the results before optimization.The laser output power exhibited very stable output with a little fluctuation between 5.77-6.02 W when the working distance changed across 1-5 m,without realigning the cavity.3.The field of views（FoVs）of the laser receiver and transmitter were optimized.We found that the CER defocusing induced by field curvature（FC）of the lenses is the main issue which limited the FoVs of the laser.Three methods to compensate the FC-induced defocusing and enhance the FoVs of the laser were proposed and experimentally investigated.The laser prototype could deliver over 5 W output when the receiver move across a working distance range of 1-5 m and rotate across a FoV of±30°,under a pump power of 16.6 W without any cavity realignment.The power fluctuation during the above process was less than 10%.The transmitter FoV at the working distances of 2 m and 5 m were～6.4°and～4.6°,respectively,within which the output power was over50%of its maximum.4.A novel method to generate the optical vortex in high-order LG modes directly from the laser resonator by means of mode selection based on spherical aberration of a defocused CER was proposed and experimentally investigated.The issues influence the mode-selection capability and cavity loss were discussed.By optimizing the pump power and components parameters to control the laser gain and cavity loss,ultra-high-order LG mode output with angular indices m of up to 95 and radial indices p>0 were obtained.The order of the LG mode output can be selected by simply adjusting the distance between the mirror and the focusing lens composing the CER slightly,and by using lenses with different focal lengths.