Dark blue Cerenkov second harmonic generation in the two-layer-stacked hexagonal periodically poled MgO:LiNbO3s

We report the dark blue nonlinear Cerenkov radiation by the second harmonic generation （SHG） in a two-layer-stacked hexagonal periodically-poled-MgO： LiNbO3s （PPMgOLNs）. Based on the direct wafer bonding of two target PPMgOLNs rotating around the axis perpendicular to the plane wi twelve bright spots as twice of those in a single PPMgOLN are shown at each second-h ring. The experimental results agree with the theoretical ones and present a promising application in the fabrication of three-dimensional （3D） PPMgOLNs.     

Generation of high-order harmonic continuum with two-hump-structure infrared laser pulse

We experimentally investigate the high-order harmonic generation in argon gas cell driven by a multi-cycle broadband infrared laser pulse from a tunable optical-parametric-amplifier （OPA） source. The generation of high-order harmonic continuum with the cut-off photon energy up to 110 eV is observed by tuning the chirp of the 800-nm laser pulse which pumps OPA source. The generation of harmonic continuum is understood in terms of the two-hump structure of the OPA output spectrum and the optimal relative phase of the two humps. The demonstrated scheme is of importance for the generation of extreme ultraviolet （XUV） continuum at higher photon energy region.     

Femtosecond pulse compression based on second harmonic generation from a frequency chirped pulse

A 49 fs pulse at the wavelength of 800 nm was converted to a 26 fs pulse at the wavelength of 400 nm by temporal stretching (frequency chirping) and second harmonic generation from a chirped pulse with subsequent compression. The energy conversion efficiency of 35% was achieved.     

利用宽带倍频特性精确测量准相位匹配晶体的极化周期

 提出了利用准相位匹配晶体进行宽带脉冲倍频,再根据准相位匹配晶体的极化周期与倍频脉冲输出中心波长的相位匹配关系来精确测量准相位匹配晶体极化周期的新方法。理论分析了准相位匹配晶体的极化周期与倍频脉冲的光谱关系、倍频容许带宽与晶体长度的关系。研究表明：宽带脉冲倍频后输出的脉冲峰值波长对应于角度的调谐曲线具有对称性;对于长度为10 mm的极化晶体,其倍频容许带宽不到0.2 nm。实验中,采用了国产PPKTP晶体试验片,晶体尺寸为10 mm×7 mm×1 mm,理想极化周期9 300 nm。结果表明：对于中心波长为537.25 nm的倍频光,其对应的实际晶体极化周期为9 303.9 nm,大于晶体加工时的理想值;当倍频脉冲光谱测量精度为0.01 nm时,准相位匹配晶体的极化周期测量精度达到0.1 nm,远高于一般光学显微镜的观测精度。     

Correlation of quadrature amplitude fluctuations during the intracavity generation of second harmonic

For the process of intracavity generation of the second harmonic, the dynamics of correlation of quadrature amplitudes fluctuations of the fundamental and the second harmonic modes is studied depending on the nonlinear coupling coefficient between the modes. It was shown that in this system the entangled states of field related to variables of quadrature amplitudes may be obtained depending on the nonlinear coupling coefficient. It was also shown that the entanglement of the states of field modes related to one quadrature amplitude may vanish depending on the value of nonlinear coupling coefficient, whereas the states of field modes related to the other quadrature amplitude stay entangled.     

CW blue light generation at 429 nm by utilizing second harmonic process with KNbO_3

Continuous-wave blue light at 429 nm from a second harmonic process has been investigated at room temperature with Potassium Niobate (KNbO3) crystal. Optimum parameters for nonlinear conversion in our designing single-resonant, external ring cavity pumped by the Ti:sapphire laser are established. 39% of maximum overall conversion efficiency is obtained and factors that limit the conversion efficiency is discussed.     

二次谐波转换对激光脉宽影响的实验研究

 实验研究了KDP晶体二次谐波转换非线性效应对脉宽测量精度的影响。结果表明：在小信号近似下,长度为1～3cm的KDPⅡ类晶体,对于近高斯脉冲,其基频脉宽与倍频脉宽存在21/2的关系;对于非近高斯脉冲,基频脉冲半宽与倍频脉冲波形的1/4高宽相等;在输入功率密度和能量转换效率较高时,基频与倍频脉宽无固定关系。     

二次谐波转换对激光脉宽影响的实验研究

实验研究了KDP晶体二次谐波转换非线性效应对脉宽测量精度的影响。结果表明：在小信号近似下,长度为1～3cm的KDPⅡ类晶体,对于近高斯脉冲,其基频脉宽与倍频脉宽存在21/2的关系;对于非近高斯脉冲,基频脉冲半宽与倍频脉冲波形的1/4高宽相等;在输入功率密度和能量转换效率较高时,基频与倍频脉宽无固定关系。     

夹持方式对KDP晶体三倍频转换效率的影响

 针对压条固定方式、粘胶固定方式和全外围夹持方式进行理论建模和数值计算分析,并讨论了不同夹持方式的优缺点及其对KDP晶体面形和三倍频转换效率的影响。研究结果表明：晶体面形形变对高斯光束三倍频转换效率的影响明显小于平面波时的情况。当入射基频光光强为6 GW·cm^-2时,对于平面波的情况,压条固定方式、粘胶固定方式和全外围夹持方式3种夹持方式相对于不考虑夹持作用时的三倍频转换效率分别减小7.5%,9.0%和7.2%;对于高斯光束的情况,三倍频转换效率分别减小了1.3%,1.0%和1.5%。