Investigation Of High Beam Quality Laser By External Cavity Combination Technology

Diode laser has widely application in the fields of industry,security and defense,because of its high efficiency,small size,long lifetime and convenient integration.Because of the poor beam quality,low output power and large divergence,many applications of diode lasers are still limited.Beam combining is an efficient approach to realize the power scaling and improve the beam quality of diode lasers.The beam combining techniques include incoherent beam combining and coherent beam combining?CBC?ways.Spectral beam combining?SBC?has an obvious advantage in improving the beam quality,but its beam quality also fails to exceed that of single element.Although CBC is a method to obtain high beam quality,it requires phase control with a resolution as high as?/10.In this dissertation,it was mainly focused on the SBC and CBC,the investigation contents and results are as follows:?1?A theoretical model was proposed to analyze the stability and efficiency of SBC.It was demonstrated that the low reflectivity of output coupler?OC?,low internal loss and short cavity were beneficial to the realization of high combining efficiency and high beam quality by SBC.However,too low reflectivity will result in an unstable combining.?2?To improve the poor beam quality of BALs in the slow axis,an off-axis SBC with selective feedback based on stripe mirror was proposed.A stripe shaped highly reflecting mirror was used to select the major lateral modes to feed back meanwhile weaken the requirements of OC reflectivity.The output power of 20.7 W was obtained,the slow axis beam quality was 4.44,and the brightness was 190 MW cm^-2 sr^-1.The M² factor in slow-axis was improved about 3.6 times by off-axis feedback compared to the single emitter.Compared with the approach of nonselective feedback,the efficiency increases 21%and brightness reaches its 2.4 times.?3?Because of the Bragg reflection waveguide photonic crystal?BRW-PC?diode lasers has the advantage of low-divergence and circular-beam,which shows a much-simplified collimation using a cheap aspheric lens.Output power of 8.8 W was achieved.Beam shrink system was used to reduce the volume of SBC system based on five BRW-PC diode lasers,the wavelength spread was narrowed about 10 times.An off-axis feedback with a stripe mirror and adjustable spatial filter was used to improve the beam quality of BRW-PC broad-area lasers?BAL?s in the slow axis.M2factor of 6.67 was realized,corresponding to 3.8 times improvement compared with single emitter.?4?SBC with dual aperture was proposed to filter high-order mode in slow axis.The output power of 34.1 W was obtained,the M² factor in slow axis was 13.5.It realized the beam quality improvement of 16%higher than that of traditional SBC.?5?Off-axis SBC of three-bar with selective feedback system was performed.A stripe was used for feedback instead of OC feedback,and the spatial filter is used for mode filtering.The output power of 34.7 W was obtained,the slow axis beam quality was 5.1,and the brightness was 290 MW cm^-2 sr^-1.The M² factor in slow-axis was improved about 3.2 times by off-axis feedback compared to the single emitter.?6?Based on scalar diffraction theory and rigorous coupled wave theory,the diffractive optical elements needed for CBC were designed and fabricated.A binary Dammann grating with a large diffraction angle??11.25^o?,small period??10?m?,and a split ratio of 1:5 was fabricated successfully.The uniformity of splitting ratio reached 10%.