Nd,Gd:SrF_(2)晶体材料在宽带放大中的光谱增益特性

Nd,Gd:SrF_(2) crystal spectrum gain characteristic in broadband laser amplification

光谱的增益窄化是影响超短脉冲宽带放大的关键因素之一.本文利用Nd,Gd:SrF_(2)晶体发射光谱的特点,开展了宽带放大中的光谱增益特性理论和实验的研究.通过数值模拟,详细研究了激光增益介质在不同的光谱增益线型及不同增益倍数下,输出光谱的演化规律.Nd,Gd:SrF_(2)晶体光谱增益窄化特性研究实验结果表明,输入光谱半高宽为5 nm时,在140倍的增益条件下,Nd,Gd:SrF_(2)晶体的输出光谱宽度未见明显窄化,实验结果与理论计算分析相符合.研究结果为氟化物晶体在宽带啁啾脉冲放大的应用奠定了基础.

Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses.In this paper,the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF_(2) crystal,i.e.the emission spectrum that has a certain width at the higher stimulated emission cross section.Through the numerical simulation,the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail.Theoretical calculation shows that the spectral gain is narrowed obviously with the increase of gain value of the traditional Gaussian emission spectrum,and that increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing.Furthermore,the spectral gain narrowing characteristics of the Nd,Gd:SrF_(2) crystal are studied experimentally.TheФ13 mm×150 mm Nd,Gd:SrF_(2) crystals are used as the gain medium which are pumped by flash lamps in the experimental study.The experimental results show that the output spectra of Nd,Gd:SrF_(2) crystals are not obviously narrowed when the full width at half maximum(FWHM)of spectral width of the input laser is 5 nm and the gain is 140 times.The experimental results are consistent with the theoretical calculation and analysis.The crystal can work normally at a repetition rate of 0.2 Hz and 1.0 Hz in the experiment,but due to the influence of thermal effect,the gain will decrease to a certain extent with the increase of pump energy and repetition rate.The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.