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11.
A tunable diode laser operating in the 4.3 m region is used to probe a conventional cw CO2 laser discharge. Vibrational populations in the 1000, 0200, 0220, and 0110 levels of CO2 are measured under lasing conditions, i.e., in the presence of intense 10.4 and 9.4 m fields. The tunable diode laser is also used to monitor the energy transfer processes between the four levels after the passage of an intense 10.4 m pulse. The detailed information provided by the tunable probe laser enables us to determineseparately all the vibration-vibration (V-V) and vibration-translation (V-T) rate constants of importance in the relaxation of the lower laser levels in CO2. The V-V rate constants are found to vary from a low value of 4.5×104 s–1 Torr–1 for the coupling of 0110 to 1000 to a high value of 8.0×105 s–1 Torr–1 for the coupling of 0110 to 0220.This work was supported by the National Science and Engineering Research Council of Canada and the Provincial Government of Ontario 相似文献
12.
Efficient collection of the scattered light from adsorbates on silver in the attenuated total reflection configuration is demonstrated with a so-called Weierstrass prism. The Raman signal from carbon contamination on silver films is enhanced by two orders of magnitude with respect to the simple external backscattering configuration. 相似文献
13.
The rotational population distribution in a free molecular jet of ethylene, C2H4, is found to be thermal over a range of distances below the nozzle (z/d=0.5–13.2, nozzle diameter d=0.50 mm). Results for on-axis rotational temperature, number density and flow velocity are presented. The average number of gas-kinetic collisions experienced by any molecule in travelling some distance along the jet axis is calculated. 相似文献
14.
G. Guillon T. Stoecklin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(3):359-371
A comparative study of the inelastic
scattering
of 14N2
+ and
14N2 in collision with 3He atoms is presented. The
unrestricted nearside-farside (NF) method proposed by
Connor [J. Chem. Phys. 104, 2297 (1995)] is applied to analyse the Close
Coupling rotationally state selected angular distributions for four kinetic
energies. These four energies illustrate different regimes of the dynamics.
The relationships between the structures of the calculated differential
cross-sections (DCS) and the different regions of the potential energy
surfaces involved which can be extracted from semi classical models are here
easily obtained from a simple reading of the (NF) figures. At the
higher energy far-off the wells (1000 cm-1) the shape of the DCS are
quite similar for the two systems and their nearside-farside components
also, showing that the inelastic process is controlled by the short range
repulsive part of the potential which is essentially the same for these two
collisions. When the energy is decreased the differences between the two
wells associated with the He–N2
+ and He–N2 complexes are
responsible for the differences between the DCS for the two systems. The
farside component associated with the well become more and more prominent
for the elastic scattering while inelastic scattering remains controlled by
the repulsive core in a large angular interval. The nearside farside
analysis gives also a new picture of a resonance which is regarded as an
equilibrium between the repulsive and the attractive parts of the potential. 相似文献
15.
A. Stampanoni-Panariello D. N. Kozlov P. P. Radi B. Hemmerling 《Applied physics. B, Lasers and optics》2005,81(1):113-129
In this article we review the results achieved in the past ten years at the Paul Scherrer Institute on the topic of diagnostics in the gas phase by laser-induced gratings (LIGs). The technique has been applied for thermometry in air and in flames at different pressures, for flow velocimetry, for concentration measurements, and for imaging purposes. The influence of collisional energy-transfer and relaxation processes in molecules on the temporal evolution of the LIG signals has also been investigated. It has been demonstrated that, for molecules with a low fluorescence quantum yield, excitation of laser-induced thermal gratings can be used as a sensitive spectroscopic tool. For the quantitative interpretation of the experiments shown in this work, the findings presented in the companion paper [1] have been used. 相似文献
16.
The temporal evolution for individual rovibrational levels of the B state of the iodine molecule is observed by two-photon delayed spectroscopy. In particular the rotational energy transfer (RET) process due to collisions of the molecules in the B state with molecules in the ground state is studied. Thermal averaged rate constants for pairs of rotational levels of the v=27 vibrational state are measured. The results are discussed in terms of the dynamics of the collision process and numerical fits to the most important parametric fitting laws for RET are presented. 相似文献
17.
V. Železny D. B. Tanner K. Kamarás L. P. Kozeeva A. A. Pavlyuk 《Zeitschrift für Physik B Condensed Matter》1995,96(3):313-318
The optical spectrum of reduced-T
c GdBa2Cu3O7– has been measured for polarizations parallel and perpendicular to theab plane. The sample was an oxygen-deficient single crystal with a large face containing thec axis. The polarized reflectance from this face was measured from 20–300 K in the spectral region from 30–3000 cm–1, with 300 K data to 30000 cm–1. Kramers-Kronig analysis was used to determine the spectral dependence of theab and thec components of the dielectric tensor. The optical properties are strongly anisotropic. Theab-plane response resembles that of other reduced-T
c materials whereas thec axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response alongc aboveand belowT
c. This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO2 planes.Permanent address: Institute of Physics, CSAV, Prague, Czechoslovakia 相似文献
18.
A. P. Smith G. Hall B. J. Whitaker A. G. Astill D. W. Neyer P. A. Delve 《Applied physics. B, Lasers and optics》1995,60(1):11-18
We describe the effects of He, Ar and N2 on the resonant degenerate four-wave-mixing spectrum of NO2. We report results obtained using the phase-conjugate and forward-geometry experimental configurations for various laser intensities and bandwidths. We find that the effect of buffer-gas pressure on the reflectivity of the laser-induced grating depends critically on the relative value of the laser intensityI to the saturation parameterI
sat. WhenI I
sat the four-wave-mixing signal initially decreases with increasing buffer-gas pressure. However, at pressures above ca. 100 Torr the signal increases. WhenI I
sat the signal is found to increase with buffer-gas pressure even at the lowest pressures studied. These observations do not agree with the standard model of degenerate four-wave mixing in the gas phase. We have investigated the source of these effects by employing different polarisation geometries of the pump and probe laser fields, and conclude that thermal gratings are responsible for the increase in signal observed at high buffer-gas pressure. This conclusion is supported by a simple gas kinetic model. 相似文献
19.
F. R. Aussenegg A. Leitner H. Gold 《Applied Physics A: Materials Science & Processing》1995,60(2):97-101
In metal-island films consisting of nanometer particles on a transparent substrate irradiated light fields can be locally enhanced by electron-plasma resonances. Therefore, nonlinear optical processes should be enhanced dramatically. However, second-order nonlinear processes as second-harmonic generation occuring in the surface are strongly reduced by the centrosymmetric shape of the metal particles. It is found that this surface-specific contribution to second-harmonic generation is less enhanced, as is expected from the field enhancement. The bulk contribution, at smooth metal surfaces known to be much weaker than the contribution from the real surface, is strongly enhanced by the plasma resonances without symmetry restrictions and becomes comparably important.Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994. 相似文献
20.
A. Liebsch 《Applied Physics A: Materials Science & Processing》1989,49(6):677-679
The nonlinear surface polarization which is primarily responsible for the surface sensitivity of optical second-harmonic generation, has recently been calculated for various simple metal surfaces and for thin adsorbed alkali overlayers. These calculations are based on the time-dependent density functional approach, i.e. the details of the ground state electron distribution at the surface as well as the self-consistent response to the applied electromagnetic field are fully taken into consideration. The nonlinear dipole moment of the induced surface charge exhibits characteristic spectral features which are closely related to corresponding features shown by the linear dipole moment. 相似文献