Design And Experimental Verification Of Large Core Size Single-mode Crystalline Wavegudie

Waveguides prepared by adhesive-free bonded technology have the advantages of low loss,high thermal conductivity and high nonlinear effect threshold,and have the potential to achieve high power,low threshold and high beam quality,which can be applied in medical,laser radar,scientific research,industry,processing and other fields.It is one of the main development directions of high-power all-solid-state lasers in the next few years.The development of high-power crystalline waveguide laser system has great market application and national defense strategic value in the future.By investigating the development status of crystalline waveguide lasers in recent years,it is found that increasing the thickness of the core leads to multimode output,resulting in a decrease in beam quality.Therefore,it is necessary to explore a method for the crystalline waveguide to maintain a single-mode output while increasing the thickness of the core,thereby making the crystalline waveguide laser system have the potential to simultaneously achieve high power and high beam quality.The single-mode condition of the crystalline waveguide is analyzed.In order to obtain the single-mode cutoff condition of the crystalline waveguide,the signal beam transmission mode in the crystalline waveguide is studied,and the characteristic equation of each mode and the dispersion curve of the crystalline waveguide are obtained.Then the concept of mode competition is introduced to further increase the single mode thickness of the crystalline waveguide.By analyzing the relative gains of different modes,the single-mode conditions under mode competition are obtained.At this time,the upper limit of the single mode thickness of the core can be determined.The correlation of the inner cladding thickness of the crystalline waveguide is analyzed,including its relationship to the number of modes in the waveguide and the pump absorption efficiency,thereby determining the extent of the inner cladding thickness.In addition,by analyzing the thermal effects of the crystalline waveguide,the thermal stress and thermal lens effect are respectively calculated to limit the pump power,and the relationship between the thickness of the outer cladding and the thermal stress is obtained through simulation.A large-core-sized crystalline waveguide was prepared,the core material is 1at.%Yb:YAG,and the size of the core is 320μm×400μm.Used it to build a crystalline waveguide laser for the experiment.In this experiment,a near-diffraction limit output was obtained,and the beam quality M~2=1.22×1.05,the maximum output power is 26W,and the optical-optical conversion efficiency is 48.5%.The experimental results show that the single-mode condition determined by the mode competition is reliable,and the design is feasible.