受激Raman谱中的宏观极化干涉

研究了Rb⁸⁵原子蒸气D1线系统中的受激Raman增益与损耗现象. 实验中观察到 随着抽运光失谐量的增大, 受激Raman谱明显地呈现出一个从增益到损耗的陡峭转变. 从缀饰态模型出发, 我们提出这是对探测光有相反贡献的不同速度原子群之间极化干涉的结果. 关键词： 受激Raman谱 电磁感应透明 极化干涉     

The first-order perturbed SBS equations

Summary Using standard multiscale techniques, a first-order perturbation theory for SBS is developed. In the presence of small damping, we find that there is a stationary solution for a soliton which is a fixed point. The velocity of this soliton is determined by the damping coefficients. In addition, there is also a constant shift in the pump intensity in the region between the front of the backward moving soliton and the forward light cone of the pump.     

A thermally stimulated discharge currents study of the molecular motions in two polysiloxane side-chain liquid crystalline polymers

The technique of thermally stimulated depolarization currents was used to study the dipolar relaxation mechanisms in two side-chain liquid-crystalline polysiloxanes. The studied polymers have the same mesogenic side-group, but they differ in the number (or density) of side groups attached to the main chain. In both cases three different relaxations were observed: one in the vitreous state, one in the liquid crystalline phase, and the glass transition relaxation. The features of those thermally stimulated discharges are discussed and some suggestions are made concerning the attribution of those discharges at the molecular level. © 1995 John Wiley & Sons, Inc.     

Stimulated-Echo NMR Spectroscopy of Be and Li in Solids: Method and Application to Ion Conductors

The generation of pure quadrupolar stimulated-echo spectra is successfully demonstrated for the spin- probe ⁹Be in a single crystal of triglycine fluoberyllate. This solid exhibits a paraelectric-to-ferroelectric phase transition. From experiments carried out for various mixing times no indications for a slow soft mode could be detected in this crystal. Then ion conducting lithium metal phosphates were studied using ⁷Li, another spin- probe which allows for a non-selective excitation of the entire NMR spectrum. In the indium and the scandium phosphates ultra-slow Li hopping processes could be detected directly via the stimulated-echo technique in a time range of up to four orders of magnitude. Due to the relatively large gyromagnetic ratio and thus strong dipolar interactions of ⁷Li no pure quadrupolar echoes could be generated. However, from a variation of the evolution times the quadrupolar effects could be separated from the dipolar ones. Finally, the differences in the ion hopping times of lithium indium phosphate and of lithium scandium phosphate are briefly discussed.     

A REMPI study of the correlation of internal excitations and substrate-adsorbate coupling for CO molecules desorbed by electron impact

We compare vibrational, translational and rotational excitations of CO molecules desorbed by electron impact, and the yield of oxygen and carbon atoms from electron-induced fragmentation of CO molecules for: (1) CO monolayers on bare transition metals [Ru(001) and Pt(111)]; (2) CO monolayers coadsorbed with well-ordered oxygen atoms; (3) weakly bound CO monolayers on epitaxially grown silver films; and (4) CO monolayers decoupled from the metallic substrate by mono-atomic xenon spacer layers. For all but the last system, we find CO molecules which are vibrationally extremely hot. This is explained by the excitation of strongly antibonding multi-electron states which are quenched in the vicinity of the metal surface before enough translational energy is acquired by the nuclei to complete dissociation. For CO/Xe/Ag(111), vibrationally hot CO molecules are missing among the desorbing particles, whereas strong fragment signals persist. Because of the isolating Xe layer, the substrate-adsorbate coupling is too weak to terminate the dissociation reaction which is induced by the electron impact before the rupture of the molecular bond.     

单纵模Nd∶YAG激光抽运CH_4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Δνp<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。     

Lasing of a DCM dye layer in carbazole-based films

We have studied the spectral and lasing properties of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in polyepoxypropylcarbazole (PEPK), polybutylcarbazole (PBK), and polyvinylcarbazole (PVK) films when excited by emission from a XeCl laser (λ = 308 nm) and the second harmonic of a YAGNd laser (λ = 532 nm). Stimulated emission was excited without an external cavity in the traveling wave mode in films of thickness 0.5–0.8 μm, obtained by the centrifuging method. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 177–181, March–April, 2006.     

Optical limiting effect based on stimulated Brillouin scattering in CCl4

The optical limiting effect based on stimulated Brillouin scattering (SBS) in a nonlinear medium was investigated. We numerically treated the nonlinear propagation process with a theoretical model, which includes the spontaneous nature of the initiation of SBS, and obtained optical limiting effect in the process. Energy limiting, pulse reshaping and stabilization have been demonstrated on SBS mechanism with the nonlinear medium CCl_4. The input optical signals were Nd:YAG nanosecond laser pulses with width varying from 16ns to 7ns then to 2ns, the relationship between the transmitted signal and launched pump signal was shown. In the experimental regime, the most stable pulse and a superior energy stabilization of the transmitted pulse were obtained when the laser pulse-width became as short as 2ns. For the energy variation of laser pulses in a wide range of 14－88mJ, the output energy was limited in a quite narrow range 4.5－5.5mJ.     

Beam Recombination Characteristics in Array Laser Amplification Using Stimulated Brillouin Scattering Phase Conjugation

Beam recombination characteristics were numerically investigated in array laser amplification using stimulated Brillouin scattering phase conjugation. To clarify the effect of piston errors due to imperfect phase locking, spatial intensity profiles of the beam recombination output were calculated in both the near and the far field on the basis of Rayleigh-Sommerfeld diffraction theory. The analyses indicate that piston errors are seriously detrimental to the quality of a beam recombination output and should be eliminated by a proper phase locking. It is also found that the gap between the beam splitting-combining wedges has a negligible effect.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Saitama, Japan.