Research On A Thin-disk Laser With Adjustable Beam Profile Based On Dynamic Gain Control

Ring beam,flat-top beam,combined beam and other laser beams with different beam profile have increasingly wide application in laser processing(drilling,welding,cutting),particle manipulation and other fields,and research around how to obtain these beams has become a hotspot.Thin-disk laser is a rapidly developing new light source,with high output power,high beam quality and other advantages.A scheme based on the principle of dynamic gain control is proposed to realize the continuous adjustment of the profile of the output laser beam from the ring to the flat top.The details are as follows:(1)The effects of the size of the Fresnel number of the thin-disk V-cavity on the loss of each order mode were calculated and analyzed using the Fox-Li iterative method and the feature vector method.The results show that the larger the Fresnel number,the smaller the difference in loss between modes.The two calculation methods are equivalent in the analysis of the fundamental mode optical field,but each has its own applicable range,which provides the theoretical basis and direction guidance for the design and verification of the resonant cavity.(2)Taking a dual-cavity structure of the thin-disk laser as an example,from the resonant cavity mode threshold analysis,the principle of dynamic gain control to achieve continuous adjustable beam profile is specified,the feasibility of the program is analyzed,and the key points to achieve the program-the design of the primary and secondary cavities are extracted.(3)The specific design and parameter selection of the resonant cavity were carried out.Based on the design objective of the primary cavity,the size of the base die spot size was analyzed and determined,and on this basis,a conforming Z-cavity was designed using the ABCD matrix.The design was then verified by calculating the loss corresponding to each mode in the cavity at different optical focal lengths using the feature vector method.The FoxLi iterative method for the active cavity was then used to obtain the threshold pumping power for each mode in the cavity.Then,according to the design requirements of the sub-cavity,the influence of the size and position of the diaphragm in the sub-cavity on its model selection was analyzed using the feature vector method to determine the optimal diaphragm size and position for the sub-cavity,thus determining the optimal parameters of the whole system.(4)Based on the designed system parameters,the experimental study of a thin-disk laser with continuously adjustable beam profile based on dynamic gain control was carried out.Firstly,we verified the correctness of our design theory by measuring the data of the primary and secondary cavities in single-cavity operation.Then,we adjust the loss of AOM in the secondary cavity under the simultaneous operation of both cavities to dynamically control the gain distribution in the central region of the thin-disk crystal,which achieves the continuous change of the beam profile from ring to flat top of the output beam of the primary cavity.In addition,the relationship between the loss of AOM in the sub-cavity and the ratio of mode to the main-cavity output beam can be obtained by curve fitting,which facilitates the rapid adjustment of the beam profile to a predetermined value.