基于铌酸锂双折射晶体的皮秒拍瓦激光系统光谱整形

为补偿皮秒拍瓦激光系统中钕玻璃宽带放大引起的增益窄化,提出了一种基于铌酸锂双折射晶体的高能量光谱整形方法.在相同强度调制下,对比了BBO、铌酸锂和石英3种晶体,针对1053 nm激光,选用了高双折射率、大口径且不易潮解的铌酸锂作为整形晶体.理论分析了晶体厚度、倾斜角、面内旋转角对强度调制的影响,发现它们分别决定调制的带宽、中心波长及深度.并对整形过程中晶体引入的光谱相位进行了分析,发现各阶色散量随晶体厚度、倾斜角、面内旋转角变化的规律,因此可通过上述参数控制各阶色散量.在此基础上,开展了中心波长为1053 nm、带宽为10 nm、调制深度为80%的光谱整形实验和相位测量实验,实验与理论分析相一致.针对神光Ⅱ皮秒拍瓦激光系统,利用上述整形方案,国内首次实现了1700 J, 6 nm (FWHM)的高能宽带激光输出,有效补偿了增益窄化.研究结果对国内基于钕玻璃放大系统的宽频带激光装置的工程研制具有重要意义.

Spectral shaping of picosecond petawatt laser system based on lithium niobate birefringent crystal

In recent years,chirped pulse amplification(CPA)technology injects vitality into the development of ultrastrong and ultra-short lasers.However,in the CPA based gain media,the gain narrowing effect limits the higher output of ultrashort pulse in energy,power,signal-to-noise ratio.In order to compensate for the gain narrowing caused by the broadband amplification of Nb:glass in picosecond pewter laser system,a method of high-energy spectral shaping is proposed based on LiNbO3 birefringent crystal,and the spectral phase introduced by the crystal is analysed for the first time.Based on the strict Jones matrix,the transmittance function of birefringent crystal and the spectral phase introduced by the crystal are obtained.Further,three kinds of birefringent crystals are compared among each other,and the results show that the higher birefringence and the smaller thickness are required to achieve the same intensity modulation.For the laser pulse at 1053 nm,LiNbO3 is selected as the spectral shaping crystal due to its high birefringence,large diameter,and non-deliquescent.The influences of crystal thickness,tilt angle,and in-plane rotation angle on the spectral intensity modulation are simulated theoretically,and the results show the above parameters affect the modulation bandwidth,center wavelength,and modulation depth of the shaping.By analyzing the spectral phase introduced by the crystal,it is found that the dispersion of each order changes with the thickness of the crystal,the tilt angle,and the inplane rotation angle,and it is the most sensitive to the change of thickness.In addition,by controlling the dispersion of each order,the influence on the pulse signal-to-noise ratio can be weakened during spectrum shaping.On the basis of theoretical analysis,the shaping experiment with a center wavelength of 1053 nm,modulation bandwidth of 10 nm,and modulation depth of 80%is carried out.And the phase introduced by the LiNbO3 is measured.The experimental results are consistent with the theoretical analysis.For the ShenguangⅡhigh-energy petawatt laser system,by the above-mentioned shaping scheme,a high-energy broadband laser output of 1700 J and 6 nm(FWHM)is realized for the first time in China,which is 2 times that at 3.2 nm when it is not shaped.The research effectively compensates for the Nb:glass gain narrowing effect,and will provide references for the parameter design,material selection and spectral phase compensation in the birefringent spectral shaping.