Study On Laser Key Technology Of Large Diameter Nd: YAG Thin Films

Thin-disk laser is a kind of novel solid-state laser, its unique construction can effectively manage the waste heat generated during the laser operation, and this allows the realization of lasers with high output power, high efficiency, and good beam quality simultaneously. Since the advent of thin-disk laser, many institutions carried out a wide range of thin-disk research on the physics and technical problems both at home and abroad. But for the large-diameter Nd:YAG disk laser, the study on the amplified spontaneous emission (ASE) in the radial direction is less, especially for the high-energy and pulsed thin-disk laser, the cognitive work that ASE influences the laser efficiency is still very limited. Depolarization in the case of small diameter thin-disk lasers is not serious, but in the large-diameter thin-disk laser, the material processing, clamping and thermal load and other factors can cause severe depolarization, which may bring on beam quality degradation. In addition, the existing thin-disk lasers are used basically in stable resonator structure, with the requirements of higher laser power and better beam quality, the study on the thin-disk lasers in unstable resonator with large mode volume in needed. So this paper mainly analyzes three aspects about the large-diameter Nd:YAG thin-disk, they are ASE features, depolarization characteristics and thin-disk lasers in unstable resonator.In the research of ASE features, the concept of the average gain length (equivalent fluorescence lifetime) is introduced, theoretical analysis give out the relationship between the average gain length and the strength of ASE. Considering the case of no laser, a self-saturation experiment is designed to compare the gain in the medium under different constructions, different pumping regions and different pumping intensity, and for different configurations each average gain length and ASE intensity are obtained under the same pumping condition. Considering laser and ASE are compatible, an experiment of flat-concave cavity is designed. Changing the pumping diameter to adjust the strength of the ASE in the thin-disk, changing the laser aperture to adjust the energy extraction, the interaction relation between laser and ASE can be analyzed. The experiment results show that the ASE lowers the output while the laser output suppresses ASE.The research of thin-disk’s thermal depolarization is constructed, finite element analysis is used to calculate the stress distribution in the disk, and then the thermal depolarization has been got. The welding stress depolarization is tested; a depolarization graph caused by the welding stress has been got. After that, an experiment is designed to realized the polarized output, a polarizer and a1/4wave plate can be combined to achieve a good polarization laser output.In the design of multi thin-disks laser in unstable resonator, a method of considering the disk as a thin lens in advanced, using the method of ABCD transmission matrix and the self-repeat of latent spherical wave to analyze the positive-branch unstable resonator which consists of six thin disks, the proper resonator parameters are given out, and an experiment with Φ40mmNd:YAG thin-disks has been carried to verify the analyze. Finally10.9J output every single pulse is realized, the magnification is2.0, the frequency is10Hz, the pulse width is250μs and the beam quality is β≈8, and to the best of our knowledge, this is the first in our country. This design method of thin-disk laser in unstable resonator is proved to be reasonable.