Parametric generation of light in arbitrary directions of a biaxial KTP crystal pumped by an Nd:YAG laser

The conditions for collinear phase matching in the parametric generation of light in arbitrary directions of a biaxial KTP crystal pumped by an Nd:YAG laser were investigated with the use of invariant expressions for the refractive indices of isonormal waves. The tuning curves, effective nonlinear coefficients, spectral and angular phase-matching widths were calculated. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 177–184, March–April, 1999.     

Thin films of silver nanoparticles deposited in vacuum by pulsed laser ablation using a YAG:Nd laser

We report the deposition of thin films of silver (Ag) nanoparticles by pulsed laser ablation in vacuum using the third line (355 nm) of a YAG:Nd laser. The nanostructure and/or morphology of the films was investigated as a function of the number of ablation pulses, by means of transmission electron microscopy and atomic force microscopy. Our results show that films deposited with a small number of ablation pulses (500 or less), are not continuous, but formed of isolated nearly spherical Ag nanoparticles with diameters in the range from 1 nm to 8 nm. The effect of increasing the number of pulses by one order of magnitude (5000) is to increase the mean diameter of the globular nanoparticles and also the Ag areal density. Further increase of the number of pulses, up to 10,000, produces the formation of larger and anisotropic nanoparticles, and for 15,000 pulses, quasi-percolated Ag films are obtained. The presence of Ag nanoparticles in the films was also evidenced from the appearance of a strong optical absorption band associated with surface plasmon resonance. This band was widened and its peak shifted from 425 nm to 700 nm as the number of laser pulses was increased from 500 to 15,000.     

利用Nd: YAG激光诱导击穿光谱法检测橡胶共混物中锌的均匀性分布

激光诱导击穿光谱是一种基于激光的定性、定量分析化学元素的方法,可用于分析混合室中的橡胶共混物。本文采用波长为1 064 nm、脉冲能量为100 mJ的Nd: YAG激光诱导击穿光谱法检测橡胶共混物中锌的分散情况。实验表明,正确混料决定了橡胶产品的质量,较短的混合时间将会导致混料的不均匀分散;焦距等参数设置对光谱线强度影响较大。激发标定样品可产生标定曲线。通过行扫描可分析锌在橡胶共混物中的分散情况。通过估算沿着行扫描方向的强度分布,可检测由于混合时间较短和旋转速度不同而引起的锌均匀性变化。     

Parametric amplification of light in a BBO crystal with pumping by YAG:Nd laser radiation

Special features of the parameteric amplification of light in a BBO crystal in the pumping field of YAG:Nd laser radiation (λ=1.064 μm) were investigated in the case in which the wavelength of the amplified signal of light lay within the eye-safe region of the spectrum and the idle wavelength lay within the region of strong absorption. The correlation between the parametric gain coefficient and the linear absorption coefficient of the crystal has been revealed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 263–266, March–April, 2000.     

Pulse shortening to 25 ps in a cw mode-locked Nd: YAG laser by introducing an intracavity etalon

The gain spectrumG(v) of a cw mode-locked Nd:YAG laser is flattened by a properly designed intracavity etalon. The increase in amplification bandwidth allows the generation of very stable trains of pulses shorter than that of standard systems. A reduction of the pulse width from 70 to 25 ps is observed by incorporating a BK 7 platelet of 420 m thickness in the resonator. The properties of the laser are investigated as a function of the thickness and the orientation angle of the etalon. The laser performance is found to be considerably influenced by the fact that the Nd³⁺ laser transition at 1.064 m consists of a line doublet.     

单纵模Nd:YAG激光抽运CH4中强后向受激拉曼散射

用单纵模Nd:YAG二倍频激光[波长532 nm,线宽△vp＜100 MHz,脉宽(半峰全宽)6.5 ns]抽运CH4气体,观察到很强的后向一级斯托克斯(BS1)受激拉曼散射,这与前人采用脉宽30 ns的单纵模抽运激光得到的绝大部分为后向受激布里渊散射(SBS)完全不同,其原因是脉宽6.5 ns与本实验条件下CH4的受激布里渊散射声子寿命接近,受激布里渊散射处于瞬态.理论计算表明,这时的受激布里渊散射瞬态增益系数已略小于后向一级斯托克斯的增益系数,而被其竞争抑制.当脉冲重复频率为2 Hz,抽运能量为95 mJ时,在1.1 MPa CH4中,后向一级斯托克斯的量子转换效率高达73%,其时间波形出现张弛振荡,脉宽被压窄到1.2 ns,从而使后向一级斯托克斯峰值功率达到了抽运激光功率的2.7倍,而且其光束质量要大大优于抽运激光的光束质量.用编制的准二维计算机模型程序相当好地再现了实验中后向一级斯托克斯的时间波形张弛振荡.     

Efficiency of fluorescence excitation in chlorophyll <Emphasis Type="Italic">a</Emphasis> by the second and third harmonics of emission from an Nd:YAG laser

We have studied the efficiency of fluorescence excitation in chlorophyll a by the second harmonic (532 nm) and the third harmonic (355 nm) of an Nd:YAG laser for sea water samples with phytoplankton taken during different algal blooms and for extracts of higher plants diluted with sea water. We have shown that when using the second harmonic, the efficiency of fluorescence excitation in chlorophyll a is more than twice as high as for excitation by the third harmonic. We discuss the advisability of using the second or third harmonics of the emission from an Nd:YAG laser when studying the biooptical parameters of sea water. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 224–227, March–April, 2008.