超短激光脉冲二倍频理论分析

采用快速傅里叶变换（FFT）算法和Rung-Kutta法对KDP晶体中超短激光脉冲二倍频过程作了研究。详细讨论了群速度失配、群速度色散和三阶非线性相位调制效应对倍频光脉冲波形、光谱及转换效率的影响。研究结果表明：在超短激光脉冲二倍频中，三阶非线性相位调制效应可使二倍频光脉冲形状发生畸变，光谱明显展宽且转换效率降低；当入射基频光功率密度大于100GW/cm2时，三阶非线性效应是影响倍频过程的主要因素。     

高聚物—富勒烯体系薄膜微微秒三倍频效应研究

采用５０ｐｓ的１．０６ｕｍ的基频光，对用物理喷束沉积方法制备的聚乙烯咔唑Ｐｏｌｙ－富勒烯组合薄膜进行三倍频信号测量。在ＰＶＫ／Ｃ６０分层膜与混合膜中观测到三倍频信号增强，考虑到两者之间的电荷转移效应，在分层膜中，把该三阶非线性增强归因于ＰＶＫ与富勒烯Ｃ６０之间的电荷转移所生成的载流子引起的电偶极矩和极化强度增强，在混合膜中，则是电荷转移所生成的络合物起主要作用。     

三阶非线性效应对三次谐波振荡转换的影响

使用快速傅里叶变换和四阶龙格-库塔法,对KDP晶体内以Ⅰ／Ⅱ类角度失谐设置方式的高强度激光三次谐波振荡转换进行了研究,考虑了谐波转换过程中的三阶非线性x^[3]、衍射、离散等效应,并着重研究了KDP晶体的三阶非线性效应对高强度激光三次谐波转换的影响。研究表明,三阶非线性效应降低了三次谐波振荡转换效率,增大了相位扰动对3ω光束的强度调制,然而通过增加二倍频的失谐角△θ8,可以避免三阶非线性效应对三次谐波振荡转换带来的不利影响。     

高功率激光的三倍频高效转换实验

利用两块φ８０ｍｍ×１４ｍｍＫＤＰ晶体，采用“偏振失配”方案在“星光”装置φ７０输出光路上，进行了三倍频实验。在入射光功率密度约为１ＧＷ／ｃｍ￣２时，获得最高的二倍频外部能量转换效率为７６．９％，三倍频最高外部能量转换效率为６６．８％，并且转换重复性和稳定性很好。同时，也通过实验研究了影响三次谐波转换的诸因素。     

干涉法测量晶体的压电系数

我们用一台泰曼干涉仪，以ＤＫＤＰ晶体的电光效应补偿由于晶体反压电效应听引起的光程差，提供了一种简单、迅速和高灵敏度测量晶体压电系数的方法．     

超短脉冲倍频中三阶非线性效应的影响及补偿

 为了提高超短脉冲二倍频的转换效率和改善出射倍频光的脉冲形状，对超短脉冲倍频中三阶非线性效应的影响进行了理论分析和数值模拟，并采用初始相位失配的方法来补偿三阶非线性效应的影响。结果表明：用KDP晶体二倍频中心波长为800 nm的超短脉冲，当入射功率密度大于100 GW/cm²时，三阶非线性效应是倍频转换效率的主要影响因素。对脉宽为50 fs，入射功率密度为250 GW/cm²的超短脉冲在KDP晶体（2 mm）中的二次谐波变换，当初始相位失谐0.9 mrad时，转换效率提高了10%，同时由三阶非线性效应引起的强度调制得到明显抑制，出射基频光和倍频光的脉冲形状得到明显改善。     

氙灯泵浦新型晶体Nd∶S－VAP调Q激光器腔内倍频研究

采用氙灯泵浦晶体Ｎｄ∶Ｓ－ＶＡＰ，ＫＴＰ晶体腔内倍频，实现了Ｎｄ∶Ｓ－ＶＡＰ晶体０．５３２５μｍ绿光激光ＢＤＮ染料片调Ｑ运转。测量了输出绿光激光的特性及不同腔长和染料片小信号透过率情况下的输出能量及脉冲宽度，给出了染料片调Ｑ腔内倍频的耦合波方程组，数值求解方程组，所得的理论数据与实验结果很好地相符     

氙灯泵浦新型晶体Nd：S—VAP调Q激光器腔内倍频研究

采用氙灯泵浦晶体Ｎｄ：Ｓ－ＶＡＰ，ＫＴＰ晶体腔内倍频，实现了Ｎｄ：Ｓ－ＶＡＰ晶体０．５３２５μｍ绿光激光ＢＤＮ染料片调Ｑ运转，测量了输出绿光激光的特性及不同腔长和染料片小信号透过率情况下的输出能量及脉冲宽度，给出染料片调Ｑ腔内倍频的耦合波方程组，数值求解方程组，所得的理论数据与实验结果很好地相符。     

倍频扫描曲线的测试及若干应用

一、引 言 当基波激光束入射到非线性晶体上时,由于非线性效应将产生倍频光(这一过程称为二次谐波产生,一般用SHG表示).倍频扫描曲线是倍频光强-温度(角度)扫描曲线的简称,是倍频晶体性能的若干重要标志之一.通过它可以了解晶体的质量、晶体的相干长度、晶体的非线性系数等重要     

铌酸钾锂晶体的光谱性质和二次谐波产生

铌酸钾锂（ＫＬＮ）晶体是一种能对近红外半导体激光进行倍频获得蓝光输出的非线性光学晶体,是人们感兴趣的一种非线性光学材料［１］。曾用多种生长技术生长了ＫＬＮ晶体,并对其倍频性能作过报道［１,２］。本文报道用电阻加热引上法从高Ｌｉ２Ｏ含量的熔体中生长的Ｋ...     

基频倍频光群速度对超短脉冲三倍频的影响分析

在超短脉冲的谐波转换过程中, 由于不同波包之间的群速度失配的存在, 非线性晶体的有效厚度、转换效率及带宽等将相互制约, 不能获得理想结果。基于耦合波方程, 在平面波和小信号近似条件下推导出了关于基频、倍频光群速度关系的解析表达式。通过对200 fs超短脉冲在II类KDP晶体中的混频过程的模拟分析, 发现在满足相位匹配的前提下, 三次谐波转换效率随着基频、倍频光群速度倒数的差值的平方呈现出指数衰减的关系, 与理论结果吻合。得出的关于基频光、倍频光群速度的表达式, 作为三倍频群速度匹配关系式的必要补充, 对寻找合适的色散晶体和选择有效的匹配措施, 实现宽带三次谐波转换具有理论指导意义。     

不同波长三倍频DKDP晶体的激光损伤

采用传统降温法,利用高纯原料从氘化程度为80%的溶液生长了四方相磷酸二氘钾(DKDP)晶体,并按Ⅱ类三倍频方式切割晶体。三倍频用DKDP晶体的最大问题在于其抗光伤阈值低于KDP晶体,严重限制了激光输出的能量密度和晶体使用寿命。考察了不同波长下三倍频DKDP晶体的损伤阈值,以及激光退火效应。实验表明,激光退火对于DKDP晶体的损伤阈值有显著的提升作用,基频、倍频、三倍频的提升效果分别达到1.4,1.9,2.7倍,是改善DKDP晶体抗光伤能力的有效途径。     

宽带三倍频混频过程的群速匹配关系

基于非线性耦合波理论分析了三倍频过程中群速度之间的关系，推导出三波混频条件下的群速匹配关系式.对超短脉冲在Ⅱ类KDP晶体中的混频过程进行了模拟分析，结果表明：当三波(基波ω，谐波2ω和3ω)的群速度满足该匹配关系式时，三倍频(3ω)的带宽和转换效率均可达最大值；而随着三波群速度对该关系式的偏离逐渐增大，带宽变窄、转换效率下降.导出的三波群速匹配关系式对寻找合适的色散晶体和选择有效的匹配措施、实现宽带三次谐波转换具有指导意义.     

Efficient frequency tripling of phase modulated laser based on two KDP mixers in tandem array

By using the cascaded KDP crystals, the third harmonic generation (THG) of temporal phase modulated broadband laser is experimentally demonstrated in this paper. The spectral characteristic of the generated third harmonic waves is investigated in detail. The experimental results show that the cascaded crystals method is able to satisfy the acceptance bandwidth of broadband laser beam. In addition, the influence on the THG spectrum and THG conversion efficiency of the air spacing between the two cascaded crystals is experimentally studied and it is remarkable on THG spectrum but insignificant for THG conversion efficiency. The relatively ideal THG spectrum is obtained by the optimal parameter of air spacing and the stability of THG spectrum is very good in our experiment.     

Broadband Third-Harmonic Generation with a Composite KD*P Crystal

We predict that broadband efficient third-harmonic generation (THG) can be achieved with a frequency-doubling crystal and a novel composite KD*P tripler. The composite KD*P tripler is made of two partially deuterated KDP crystals with different deuteration levels by using the thermal bonding technique. The deuteration level of a partially deuterated KDP crystal is used as a degree of freedom to alter the phase-matching (PM) wavelength. Simulations show that the composite KD*P tripler can improve third-harmonic conversion efficiencies over a very wide band of input fundamental frequencies. In terms of robustness, alignment and stability, this THG scheme should be more promising than other broadband THG approaches because the composite KD*P tripler is a monolithic device.     

Inverse problem of cascaded third-harmonic generation

Based on some numerical techniques such as split-step Fourier transformation, fourth-order Runge-Kutta and successive iteration method, the fundamental field was calculated from the known third-harmonic (TH) field in the process of TH generation (THG) using one doubling and one mixing KDP crystals. The effects of the monochromatic initial fields on the iteration numbers and the calculation precision were discussed. The inverse solution of the broadband laser pulse with linear frequency chirp was also carried out. The results show that the method proposed in this paper is available and efficient, which gives a new way to design and optimize the process of THG.     

Cascaded third-harmonic-generation converter based on a single ADP crystal

Based on a specially designed optical structure, an efficient cascaded third-harmonic-generation(THG) output of a 1064-nm, pico-seconds pulse laser is successively realized by using an NH_4H_2PO_4(ADP) crystal that acts as the secondharmonic-generation component and sum-frequency-generation component. The maximum THG output is 1.61 mJ, and the highest conversion efficiency from 1064 nm to 355 nm reaches 35%, which are obviously superior to the results obtained using a KDP crystal under the same circumstance. The further phase-matching analysis indicates that this THG configuration of ADP crystal can be applied to various fundamental wavelengths in a range of 1 μm–1.1 μm. Compared with the previously reported KDP THG converter, which is based on a similar principle, the present ADP THG converter is favorable for large-energy, high-efficiency operation because of the larger effective nonlinear optical coefficient deffand higher laser damage threshold.     

双波长双脉冲激光三次谐波的产生方法

提出双波长双脉冲激光产生三次谐波的方法。波长不同的两脉冲激光束由反射使它们合拢后通过两块非线性的BBO晶体 ,激光脉冲第一次通过BBO晶体产生两波长的二次谐波 (SHG) ,它们由各自的反射镜反射再次通过BBO又产生了二次谐波 ,这两次产生的二次谐波和基波通过用于产生三次谐波的BBO晶体可产生双波长的三次谐波 ,它们由 45°斜置的耦合镜输出。文中分析了满足二次谐波和三次谐波的四个相位匹配的条件 ,该方法也可用于腔内双波长双脉冲的三次谐波激光的产生 ,给出了相应的实验结果。     

Analysis of broadband third harmonic generation with non-collinear angular dispersion in KDP crystals

A new scheme with non-collinear sum frequency generation (SFG) process of broadband third harmonic generation (THG) with two KDP crystals (one doubler and one mixer) using angular dispersion was proposed. The principle of broadband harmonic generation with non-collinear angular dispersion was presented. The comparison between the schemes of non-collinear and collinear SFG process was performed. The effects of the angular dispersion on the conversion efficiency, the pulse shape and the spectrum of the third harmonic field were discussed. The results show that, if proper angular dispersion is added to the fundamental and the second harmonic field outside the mixing KDP crystal, respectively, the broadband third harmonic conversion efficiency can be improved significantly. However, the difficulty of this scheme arises due to the requirement of two gratings with different angular dispersion outside the mixer. With the new scheme, it can be simpler that only one grating is needed to realize the broadband phase matching in the non-collinear SFG process. Although the fundamental and the second harmonic field inside the mixing crystal are non-collinear except the center wavelength, a blazing grating with proper angular dispersion for the fundamental field (twice as that for second harmonic field) can yield the well compensation for phase mismatching in the SFG process. Consequently, the conversion efficiency and the characteristics of the third harmonic field for the broadband third harmonic generation can be improved significantly.     

单轴晶体三阶有效非线性系数的解析表达式

应用压缩角标方法所得到的三阶非线性系数的矩阵形式，首次给出了在单轴晶体事进行三次谐波实验时，各种相位匹配方式下，其三阶有效非线性系数的解析表达式。这些表达式对三次谐波实验具有指导意义。