中文摘要：

体光栅光谱组束是获得高功率激光输出的一种有效途径.在有限的可用带宽内,光谱通道间隔影响着组束光束数目以及最终的高功率组束输出.采用耦合波理论,建立了一个两通道高功率光谱组束模型.通过优化体光栅光谱通道间隔,可放宽对组束子束线宽和功率的限制,组束功率可大幅提升而光谱密度并无显著下降.基于此,实验上获得了2.5 kW组束输出,绝对效率超过85%,通道间隔5 nm,光谱密度为0.51kW/nm.组束功率〈1 kW时,组束输出能保持好的光束质量;组束功率〉1.5kW时光束质量恶化较明显,通过分析发现,组束光束质量的恶化主要受限于体光栅的色散及高功率下体光栅复杂的热畸变.

英文摘要：

Spectral beam combination based on volume Bragg gratings is an effective approach to obtaining high power laser output.In spectral beam combining system,spectral channel spacing will affect the number of non-combined sub-beams and the overall combined output power due to the finite available gain bandwidth.Based on coupled wave theory,a two-channel high power spectral beam combining model is proposed.By appropriately relaxing the requirements for the spectral channel spacing and line-width of sub-beams,the higher combined output power can be obtained but the spectral density does not significantly decrease.In this work,a 2-channel spectral beam combining system is demonstrated to present a 2.5 kW combined power with combining efficiency 〉85%by employing a transmitting volume Bragg grating.The combining system has a high spectral density of 0.51 kW/nm with 5 nm spectral spacing between channels.The output can keep a good beam quality when the combined power is less than 1 kW,while the significant degradation of combined beam quality occurs when output power is 1.5 kW and is restricted mainly by the dispersion properties and thermal effects of volume Bragg gratings.During this 2-channel beam combining process,no special active cooling measure is used.Interactions between laser radiation and the grating are verified.Thermal absorption of high power laser radiation in the grating will cause the temperature to remarkably increase,resulting in the thermal expansion of the grating period,which leads to the degradations of diffraction efficiency and the spectral selectivity.Research is also focused on the surface distortion,and the results indicate that the thermal-induced wave-front aberrations of the noncombined sub-beams lead to the deterioration of beam quality.Transmitted and diffracted beams experience wave-front aberrations to different degrees,leading to distinct beam deterioration.