Spectral Beam Combining Of Diode Lasers Based On V-shaped External Cavity

Semiconductor lasers have many advantages including high efficiency,small size,light weight and wide band coverage,and have been applied in pumping of fiber lasers,material processing,telecommunication and sensing.Based on the broad-area waveguide and large-optical-cavity structure,the emission power of diode lasers was enhanced significantly.However,the beam quality in slow axis becomes poor.Beam combining is an effective approach to improve beam quality and increase the brightness of diode lasers.Currently,the combined diode laser with continuous wave?CW?power of 8kW and M²¹1 had been demonstrated by spectral beam combining?SBC?under the manner of external cavity,which is the best brightness and beam quality realized by non-coherent beam combining.However,there exists a beam-quality limit in SBC,i.e.the highest beam quality is able to be near that of single emitter but can not be better than the single emitter,which means that if want to improve the beam quality of combined lasers furtherly,it has to improve the beam quality of single emitter.To solve this beam-quality limit,this thesis was focused on the investigation of beam combing method.In this thesis,it starts from the study of basic mechanism of SBC,a novel SBC method based on V-shape external-cavity was proposed and demonstrated the breaking of beam quality limit of SBC.The following achievements were realized.1.To improve the beam quality limit of conventional external-cavity SBC system,a small-angle V-shape external-cavity SBC method was proposed?VSBC?.The beam quality of VSBC exceeds the beam quality limit of SBC proposed by MIT Lincoln Laboratory in 2000.The beam quality M²².31?3.76 in fast and slow axes was obtained,which is the best beam quality realized from a commercial laser array at the same output power.A USA and a Chinese patent?201711171795.2?have been applied.2.A V-shape external-cavity feedback method was used to improve the brightness of single laser.The brightness of 192.05 MWcm^-2sr^-1 was obtained from a single laser with a stripe width of 90 microns,which shows a 6.5 times improvement at the same current.3.Based on the theory of semiconductor external-cavity SBC,the external-cavity feedback beam combination of a 980 nm bar was realized and the maximum CW output power was 21.9 W.Fourier lenses with focal length f=250 mm,300 mm and 400 mm were selected as transmission lenses to construct the combining system.The output power,beam quality and spectra after combining for these three different systems were analyzed.The relationship between the focal length of Fourier lens and the spectral width after combining was obtained.