Fluorescence polarization of helical molecules cooled in a supersonic jet

The β-binaphthylene oxide molecules studied under supersonic cooling conditions have a number of specific properties due to their nonplanarity. Low-frequency vibrations of the molecules in the excited S1 state are higher than the frequencies for the S0 state, and conversely the high-frequency vibrations have lower frequencies. The S₀-S₂ fluorescence excitation spectrum is structureless. The absence of a Q branch in the rotational contour of the line for the purely electronic transition indicates that it is substantially broadened and shifted toward shorter wavelengths as a result of rotational perturbations of the helical structure of the molecule. Multiplet lines in the spectra of β-binaphthylene oxide complexes with argon, krypton, and xenon correspond to different isomeric complexes. Their bond energies are below those observed previously for planar polycyclic molecules such as perilene, fluorene, and carbazole. The greater number of isomers with xenon is due to strengthening of the bond in the van der Waals complex and the nonequivalence of the position of the xenon atoms on the outside and inside of the helical molecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 473–477, July–August, 2006.     

Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

We have recorded the fluorescence excitation spectra of three heterocyclic compounds with a chain structure [BPO (2-phenyl-5-(4-diphenylyl)oxazole), POPOP (1,4-di[2-(5-phenyloxazolyl)]benzene, and TOPOT (1,4-di[2-(5-n-tolyloxazolyl)]benzene] and the fluorescence spectra of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation, vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded starting from ν ₀ ⁰ + 200 cm⁻¹. For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm⁻¹, arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic transitions of the POPOP molecules (T_rot = 10.5 K) and TOPOT molecules (T_rot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence P_fl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm⁻¹ above ν ₀ ⁰ is practically constant (∼8.4%) and matches P_fl for high-temperature vapors. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 728–734, November–December, 2006.     

Fine-structure spectroscopy of 2-methylnaphthalene cooled in a supersonic jet

The fluorescence and fluorescence excitation spectra of 2-methylnaphthalene molecules cooled in a supersonic jet are measured. The frequencies of vibrations in the S ₀ and S ₁ states, as well as the relative intensities of electronic-vibrational transitions in the fluorescence and fluorescence excitation spectra, are calculated with the semiempirical MO/M8ST method. The intensities are calculated in the Franck-Condon approximation taking into account the mixing of all the 38 totally symmetric normal vibrations. Based on the calculations, most observed spectral lines are assigned. It is shown that the calculation accuracy of the method is high enough for it to be used to interpret the spectra of molecules of aromatic compounds such as substituted naphthalenes. It is found that the main contribution to the fluorescence spectrum is made by four optically active vibrations.     

Manifestations of the saturation effect in the polarization of the fluorescence of quinizarin molecules cooled in a supersonic jet

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 4, pp. 567–572, October, 1990.     

射流式水冷镜结构优化设计

分析了影响射流式水冷镜形变的各种因素,利用ANSYS有限元分析软件,对各项结构参数对镜体形变的影响进行了数值模拟,探索出射流式水冷镜结构设计的一般规律,得到了镜体结构的优化设计方案。数值结果表明：在镜体直径80 mm、镜面净吸收功率100 W、光斑直径25 mm、使用硅作为镜体材料的情况下,射流式水冷镜镜面最大形变可低至0.07 μm,明显优于其它类型的水冷镜。     

射流式水冷镜结构优化设计

 分析了影响射流式水冷镜形变的各种因素,利用ANSYS有限元分析软件,对各项结构参数对镜体形变的影响进行了数值模拟,探索出射流式水冷镜结构设计的一般规律,得到了镜体结构的优化设计方案。数值结果表明：在镜体直径80 mm、镜面净吸收功率100 W、光斑直径25 mm、使用硅作为镜体材料的情况下,射流式水冷镜镜面最大形变可低至0.07 μm,明显优于其它类型的水冷镜。     

The characteristics of multiple-photon absorption of SF6 molecules cooled in free jet expansion from a pulsed supersonic nozzle

The multiple-photon absorption of pulsed TEA CO₂ laser radiation by SF₆ molecules cooled toT _R40K andT _v160K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J·cm^–2.For practically all laser lines which coincide with the linear absorption spectrum of thev ₃ vibrational mode of SF₆ [P(12)...P(28), 10,6 m], the dependence of the absorbed energyE _ab on the exciting energy fluence was found to be steeper than linearE _abⁿ, wheren=(1.1 to 1.8). Considerable increases of the absorption cross sections with increasing energy fluence were observed.The fraction of the molecules interacting with the laser radiation is estimated.     

低温高背压氘团簇源特性研究

为了产生大尺度氘团簇用于与强激光相互作用研究，研制了低温高背压团簇源.利用瑞利散射法对团簇尺度与气体背压相关性和团簇的形成演变过程进行了研究.得到团簇尺度N_c随背压的指数变化关系为N_c∝P^2.89₀，当气体温度为80K，背压P₀为48×10⁵Pa时，氘团簇尺度N_c≈2630，并得到了团 关键词： 氘团簇 团簇源 瑞利散射 激光与团簇相互作用     

Pump-probe spectroscopy of atoms cooled in a 3D lin lin optical lattice

We describe the pump-probe spectroscopy of atoms cooled in a 3D lin⊥lin optical lattice. Our pump-probe configuration consists of two laser fields detuned with respect to the lattice fields. This scheme allows to clearly identify in the probe transmission spectrum the Brillouin and Raman resonances, by studying their positions as functions of the angle between the pump and probe beams. We describe these resonances in detail, and compare the experimental results to the theoretical predictions. Our conclusions are supported by transport-spectroscopy measurements, which allow to distinguish between contributions to the light scattering from propagating and non-propagating atoms. Received 8 April 2002 / Received in final form 9 September 2002 Published online 12 November 2002     

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformations of He-jet-cooled trimethyl[(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S₀–S₁ transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C - H ?O < _C^Si C - H \cdots O <_C^{Si} between hydrogen atoms of methyl groups and an oxygen atom and C–H···π between H and the π-electron cloud of the indole ring.     

Laser spectroscopy of cooled zirconium fission fragments

The first on-line laser spectroscopy of cooled fission fragments is reported. The r ions, produced in uranium fission, were extracted and separated using an ion guide isotope separator. The ions were cooled and bunched for collinear laser spectroscopy by a gas-filled linear Paul trap. New results for nuclear mean-square charge radii, dipole, and quadrupole moments are reported across the N=60 shape change. The mean-square charge radii are found to be almost identical to those of the Sr isotones and previously offered modeling of the radial changes is critically reviewed.     

激光相干合成中单元的相位和振幅波动对合成光束远场分布的影响

运用傅里叶光学分析法推导出系统抖动造成单个光源的相位和振幅发生波动时的远场光强表达式,以1维阵列为例分析了系统抖动对远场的影响。研究表明:随着参与合束的发光单元数目的增加,尖峰变锐,能量更集中;系统抖动引起了远场峰值光强的减少,出现了本底现象,破坏了远场的对称性和光束质量;激光阵列单个光源的相位随机抖动应该控制在3/8范围内;相干合束发光单元数目越多,系统抖动对远场的影响越小。     

射流式水冷镜对流换热系数的优化

介绍了射流水冷技术并将其应用到高能激光器反射镜的冷却中,设计了射流式水冷镜。采用计算流体力学的方法,利用通用有限元软件ANSYS的流体分析模块FLOTRAN对单孔内射流进行了数值模拟,详细讨论了各孔参数对换热性能的影响,实现了孔参数的优化。结果表明:在水冷镜中采用射流技术可以获得很好的对流换热效果,换热系数可达100 kW/(m2·K)以上,且具有结构简单、可控性强等特点。     

Ultrahigh-resolution saturation spectroscopy using slow molecules in an external cell

We present the narrowest molecular lines so far recorded in the 10 µm spectral region. A linewidth of 80 Hz (HWHM) has been obtained for theP(39)A ₁ ³ (–) line of OsO₄, by selecting slow molecules (T _eff=0.6 K) in saturation spectroscopy at low laser fields (30 nW) and low pressures (2 × 10^–6 Torr). In these conditions, the contribution of the fast molecules is greatly reduced because of the finite size of the beam. This method, applied previously to methane at 3.39 µm, is used for the first time in an external cell and improves by a factor 8 the best resolution of our spectrometer. Heterodyne detection and double frequency modulation have been necessary to extract a signal at a contrast of only 10^–6. The physical ideas concerning this regime are described and a detailed analysis of the line shape is given.     

Saturated absorption spectroscopy of acetylene molecules with an optical nanofiber

We performed saturated absorption spectroscopy of acetylene (C?H?) ν? + ν? band transitions with an optical nanofiber (ONF). Owing to high-intensity light around the ONF, we observed a Lamb dip at relatively low-power laser (~10 mW) without a cavity. Our results showed that the simple ONF spectrometer is advantageous for performing saturation absorption spectroscopy and serves as a practical low-cost wavelength reference in the optical fiber communication band.