Research On The Beam Combining Technology Of The External Cavity Spectrum Of The Semiconductor Laser Without Output Coupling Mirror Grating

Diode lasers play an important role in many applications such as pumping of solid-state lasers,display,and material processing.The commonly used diode laser output beam combining methods include space beam combination,polarization beam combination and spectral beam combination.Among them,spectral beam combination(SBC)can increase the brightness by several times while keeping the quality of the output beam equal to that of a single emitter.Therefore,it has gradually become a research hotspot and has achieved some big breakthroughs.In recent years,Teradiode has maded the output power of diode laser spectral reach several kilowatts by spectral beam combining technology.This dissertation focuses on the study of one of the wavelength division multiplexing techniques——spectral beam combining technology of diode lasers.The scheme of the coupler-free grating-external cavity spectral beam combining was designed,and a high-power,high-beam-quality,high-brightness spectral beam combining direct output diode laser light source was developed.The specific work is as follows:1)The promising methods and recent major achievements in the development of spectal beam combining technology for high-power high-brightness direct diode laser sources at home and abroad have been combed.The wavelength beam combining,spectral beam combining(dense spectral combining technique and coarse beam combining technique),and wavelength division multiplexing of diode lasers are unified as wavelength division multiplexing beam combining technology.The development status of wavelength locking and multiplexing components used in wavelength-division-multiplexing beam combining technology of diode lasers and currently available commercial wavelength division multiplexed direct diode laser sources are summarized.2)For the purpose of improving the output power,the beam combining efficiency and the beam quality of the combined beam,the output-coupling-mirror grating-external cavity spectral beam combining method is analyzed,and the coupler-free grating-external cavity spectral beam combining structure is designed.The composition of the feedback beam and the output beam of the coupler-free structure is analyzed and explained,and its equivalent external cavity structure is obtained.3)The principle and process of wavelength locking in the external cavity of diode laser are analyzed.A brief analysis of the external cavity structure parameters and external cavity feedback coupling bandwidth in the spectral beam combination of grating external cavity is established and the relationship between the coupling bandwidth and the residue spectral linewidth of the diode laser emitter is analyzed.4)The principle of spectral beam combining in grating external cavity is analyzed.According to the characteristics of grating dispersion,the wavelength-angle correspondence system of grating was established with grating grating line 1600 lines/mm and grating Littrow angle aLittrow=51.3°@976nm.According to the established wavelength-angle correspondence system,the influence of the interval between the diode laser array emitters,the focal length of the transform cylindrical lens,the grating period,and the Littrow angle of the grating,etc.,on the spectrum peak-to-peak intervals and the total output spectrum width of the combined beam output is discussed.The main reasons,the residual spectral line width,the cross talk between the emitters,and the "smile" of the diode laser array,leading to the deterioration of the beam quality of the output beam are analyzed.5)A nine-emitter diode laser array of 976nm was tested for the purpose of performing single-array coupler-free spectral beam combining experiment.The output power of 40.8 W at a working current of 70 A was achieved in the single-array experiment,which verified the feasibility of an external cavity structure without an output coupling mirror.6)Based on the beam combining verification experiment of a single array,an experiment program for high-power direct diode laser source was developed,in which six array were stacked in the direction of fast axis and then two such stacks were spatially combined along the slow axis.A set of direct diode laser source with an output power of 578W,electro-optical efficiency of 46.5%was obtained successfully,and the beam quality for fast axis and slow axis are respectively 7.35mm-mrad and 6.03mm·mrad(including 95%energy),and space brightness is approximately 132.14MW/(cm2·sr),spectral brightness is approximately 12.88MW/(cm2·sr·nm).