Research On Spectral Beam Combining Based On High Fill Factor Laser Diode Bar

Spectral beam combining(SBC)is one of the methods to achieve high beam quality and high output power.The higher the fill factor of the laser diode bar means higher beam combining efficiency and output power,more serious slow-axis collimation problems and crosstalk problems.This thesis is the first domestic theoretical and experimental study on the crosstalk in the spectral beam combining of the 80% fill factor laser diode bar,which has certain theoretical significance for the future development of spectral beam combining.A crosstalk model is established,and a spatial filter is added to eliminate crosstalk.The main research contents are as follows:(1)The slow axis collimation of high fill factor laser diode bar is studied.A combination structure,including fast-axis collimator,image transmission system,beam rotating mirror and slow-axis collimator,is designed to solve the problems of insufficient space and poor collimation effect.The angles,after been collimated,are 3.49 mrad and17.45 mrad,respectively.The collimation effect is good.(2)A model of crosstalk in spectral beam combining with high fill factor laser diode bar is established.The light source model is improved.A single emitting is simulated by multiple Gaussian beams arranged along the slow axis,and a beam propagation model of the SBC system with crosstalk is established.Five individual beams are taken for example.The width of the combined beam spot is 3.5mm in the near field,and 0.48 mm in the far field.The distances between the various levels of crosstalk spots and the main spot are0.78 mm,1.56 mm,2.34 mm,and 3.12 mm respectively.The spectral interval between neighbor peaks is 1.84 mm,and the wavelengths of the crosstalk light are the intermediate values of the wavelengths of the two emitters where the crosstalk occurs.Without crosstalk,M2=5.2;with crosstalk,M2=15.4,indicating that the crosstalk deteriorates the beam quality.(3)The crosstalk existing in SBC with high fill factor laser diode bar is studied experimentally,and the optical field distribution of the main spot and crosstalk spots is observed in the far field.A spatial filter composed of a Kepler telescope system and an aperture on the confocal surface is added between the grating and the output coupling mirror to eliminate crosstalk.Without crosstalk,the spot width is 0.73 mm in the near-field,and 0.31 mm in the far-field;M2=11.5;and the combined laser power is 3.6W with 9emitters.