| High power semiconductor laser has become one of the main light sources in the field of laser processing and an important pump source of fiber laser.Due to the structural characteristics and packaging factors of semiconductor lasers,the emitter has low output power,poor beam quality and low power density,so it is necessary to obtain high power and high beam quality output through beam combining and other technologies.Spectral beam combining of semiconductor laser is a technology that locks the beams of multiple semiconductor laser emitters at different wavelengths and combines them at the same diffraction angle by optical scattering elements and external cavity feedback.Based on the spectral beam combining technology of semiconductor laser,the optimization of the total power and beam quality of the combined output beam has been deeply studied,which is of certain significance for the further development of spectral beam combining technology.The main research contents are as follows:(1)The basic structure of the external cavity feedback spectral beam combining system of semiconductor laser based on plane grating has been analyzed,the design and simulation of the spectral beam combining system have been carried out.The influence of each component in the spectral beam combining system on the combining effect has been analyzed.The residual divergence angles of the system simulation after fast and slow axis collimation are 1.900 mrad and 6.100 mrad respectively,which means the collimation effect is good.The beam quality in fast and slow axis direction of five laser emitters combining are 0.336mm·mrad and 0.494 mm·mrad respectively,and the common aperture output has been successfully realized.(2)The parallel plate mirror group has been used in spectral beam combining system to achieve higher power output under the same linewidth.In order to solve the problem of small number of combinable laser emitters and low total output power caused by the excessive spectral interval between adjacent emitters in the spectral beam combining of semiconductor laser array with low duty cycle,a beam shaping structure composed of parallel plate mirror has been adopted,which can shape the laser beam before beam combining to reduce the linewidth between combined emitters and increase the total number of laser emitters that can participate in beam combination.In this thesis,two semiconductor laser arrays with central wavelength of 808 nm are used as beam combining sources.The spectral beam combining system with shaping structure has been theoretically deduced and simulated by software.The spectral beam combination of two laser bars has been realized.Compared with the traditional spectral beam combining system without shaping structure,the maximum number of combined emitters has been increased from 5 to 10 within a line width of 7 nm,which has successfully improved the output power of the beam combination.(3)The influence of grating dispersion on the output beam quality of semiconductor laser spectral beam combining has been studied,and the double-grating beam combining structure has been used to eliminate the beam quality degradation caused by grating dispersion.The output beam quality of single grating and double-grating spectral beam combining has been simulated and compared,and the optimization effect of double-grating spectral beam combining structure on beam quality has been verified.The output mode of single emitter in the double-grating external cavity feedback structure has been further deduced,and the relationship between the output mode and grating parameters in the double-grating beam combining structure of semiconductor laser has been analyzed.It is found that more stable and high spectral purity output can be obtained by increasing the number of grating lines irradiated by the beam and the diffraction efficiency of the grating.(4)The structural factors affecting the inherent crosstalk beam intensity between the combining emitters in the spectral beam combining structure of semiconductor laser have been analyzed theoretically for the first time.The results show that the focal length of the transmission lens,the distance between the grating and the output coupling mirror,the distance between adjacent laser emitters and the beam waist radius of a single laser emitter can all affect the output crosstalk intensity of the spectral beam combination.Reducing the focal length of the transmission lens,increasing the spacing between the grating and the output coupling mirror,increasing the spacing between adjacent laser emitters and the beam waist radius of a single emitter can reduce the inherent crosstalk of the system.(5)Several groups of spectral beam combining contrast experiments have been carried out to verify the influence of the structural parameters of the beam combining system on the inherent crosstalk intensity between the beam combining emitters.In the experiments,the semiconductor laser array with a filling factor of 80% is used as the combined light source,and the far-field optical distribution of the main spot and each crosstalk spot has been measured.When the distance between the grating and the output coupling mirror is 50 mm and the focal length of the transmission lens is 200 mm,the ratio of the first-order crosstalk peak energy to the peak energy of the central beam spot is about 0.34.When the distance between the grating and the output coupling mirror is 300 mm,the ratio decreases to 0.035.When an inverted Kepler telescope with a magnification of 2 is added before the transmission lens,the ratio decreases to 0.085.When the focal length of the transmission lens is 80 mm,the ratio has been reduced to 0.07.The experimental results have proved the influence of the structural parameters on the inherent crosstalk in the spectral beam combination system,and the inherent crosstalk can be suppressed by increasing the spacing between the grating and the output coupling mirror,adding an inverted Kepler telescope to expand laser beam or reducing the focal length of the transmission lens. |
PDF Full Text Request