Output Mode Controllable Solid State Laser

Coherence is one of the important characteristics of laser,which has different requirements in different application fields.Therefore,how to obtain the coherent degree controllable laser has become a hot research topic.The method of adjusting laser coherence has direct method and indirect method,that is,directly adjust and control the coherence distribution from the laser resonator,or indirectly adjust and control the laser coherence degree by adding optical elements(such as rotating frosted glass,Spatial Light Modulator,etc.)outside the laser resonator.In view of the importance of partially coherent beams with controllable spatial coherence,this thesis focuses on the study of degenerate cavities,the main research contents are listed as follows:1.We experimentally investigate a kind of lasers delivering partially coherent light beams with controllable coherence.The laser rod Nd:YAG is pumped by laser diode(LD),and the laser resonator is consisted of two flat mirrors,and two lenses.The two lenses are placed inside the resonator to form a degenerate laser cavity,and a spatial filter is placed between two lenses.We show that the number of transverse mode of output laser can be controlled by varying the size of thespatial filter,so that the spatialcoherence can be controlled.The influence of the size of the spatial filter on the mode number,spatial coherence is studied.It is shown that decreasing the size of the spatial filter will result in the decreasing of the mode number,and increment of the spatial coherence.It is also shown that the increasing of the size of the spatial filter will lead to lower spatial coherence.The KTP crystal is inserted into the degenerate cavity above,and the green light of 532 nm with adjustable coherence can be directly output by adjusting the size of the spatial filter and the size of the input power.The experimental results show that increasing the size of the spatial filter and the size of the input power will reduce the coherence of the output green light.2.The Pr:YLF crystal was end-pumped by a 445 nm blue semiconductor laser.The multi-wavelength excitation is achieved by inserting two lenses with a focal length of 50 mm into the resonant cavity to form a 4f telescope system(degenerate optical cavity).The wavelength of 604 nm,640nm and 698 nm can be obtained.The experimental results show that these three wavelengths laser exist competing effect,and it is observed that three or two wavelength laser can be generated simultaneously.We also find that only single wavelength640 nm is obtained without 4f system present.3.The Pr:YLF crystal was end-pumped by a 445 nm blue semiconductor laser,under certain conditions,the higher-order Laguerre-Gaussian(LG)beam and the higher-order Hermite-Gaussian(HG)beam of wavelength 640 nm was directly delivered from the plano-concave laser cavity.The intensity distribution characteristics of higher-order LG beams and higher-order HG beams were theoretically studied,and the numerical simulation results are given.The experimental results show that the higher-order LG beams and the higher-order HG beams from the laser cavity are in agreement with the theoretical simulation.