Doppler profiles, experimental

Fig. 12.8. a The pulse duration dependence of the Heai line shape for a fixed laser energy of 49 mJ. Open circles, triangles, and squares represent experimental data for pulse durations of 30, 500, and 1000 fs, respectively. The solid, dotted, and dashed lines represent Doppler profiles obtained by fitting the central part of the line to the experimental data, b The pulse duration dependence of the kinetic energies of He-like argon ions calculated from the Doppler shift... 

North and Hall [68] used FM spectroscopy to obtain Doppler profiles of the nascent CN produced by this reaction. A feature of their experimental results is that the Q and R branches for the same rotational state of CN exhibit nearly identical Doppler profiles. This result indicates an absence of vector correlations in the dissociation these correlations should occur in an impulsive reaction, where one would expect v 1 j. Their results suggest that the dissociation occurs as a statistical fragmentation after internal conversion to the ground state rather than as an impulsive one via an excited state. 

A comparison was made between the experimentally determined Doppler profiles and those profiles predicted by PST [35] for each detected state. In order to make the correct comparison, the PST velocity distribution, which is in the center-of-mass frame, must be first averaged over the room temperature Boltzmann distribution of the parent, and then convoluted with the parent velocity distribution. This calculated laboratory distribution can then be converted to a Doppler profile and compared to experimental data. A comparison can also be made between the experimentally determined values and those calculated by PST. The transformation between the two frames is given by [80]... 

Pigure 5.31 shows the experimental Doppler profiles for CO J) products from the photodissociation of OCS with 222 nm laser light. The interesting feature is that horizontal (0 =0) and vertical (0 = 90°) laser polarization does not give the profiles expected for uncorrelated distributions. Por instance, the profile for the Q(58) transition appears to have a P value of about 0.8 when measured with horizontal polarization, while it has a P value of slightly less than 0 when measured with vertical polarization. Purthermore, the Doppler profiles are completely different in the P(58) transition even though the same initial state (J = 58) is being excited. 

Figure 5.31 The experimental Doppler profiles for the OCS dissociation. The rotationally resolved product CO was measured by FE. Taken with permission from Sivakumar et al. (1988). 

Another advantage of polarization spectroscopy is the suppression of the broad signal back-ground observed in saturated absorption (Fig. 16a), when collisions redistribute the velocities of the pumped atoms over the Doppler profile, because these velocity-changing collisions drastically reduce the laser-induced anisotropy (the curves in Figure 16 are obtained in the same experimental cell of neon). A good review about Polarization Spectroscopy and related phenomena can be found in ref. I 25 I. 

The experimental results are described in Section II. The shapes of the Doppler profiles are accounted in Sec. Ill in terms of the specific alignment of the rotational magnetic quantum numbers and the angular distribution of the CO photofragments. 

Fig. 1. Experimental and calculated data for the Q(56) and R(56) lines of CO. First row (left to right) Calculated I(cos0) functions. Second row Calculated D(cos0) functions (solid curves) the Gaussian laser line width is shown in the dashed curve. Third row Experimental (dots) and calculated (solid curve) Doppler profiles. The curves are synthesized using the values 0=0.8, FWHM laser linewidth=0.14 cm The magnitude of the C0 s velocity is calculated Vo=1430m/s. The Doppler profiles are computed for a circular polarized monitoring beam.

The left panels correspond to the Q(56)transition with a perpendicular excitation mode a=90°, the middle panels are for the Q(56) with a parallel excitation mode o=0. The right panels correspond to a perpendicular excitation of the R(56) transition. The upper row displays the calculated correction function I(cos6). The middle panels display the angular distribution function D(cos6). These curves should describe the Doppler profiles in the absence of any v-J correlation. A comparison between experimental and calculated Doppler profiles is shown in the bottom panels. Only one parameter namely P 0.8 is used in calculating the three curves. It is clear from the figure that the line shapes in the absence of a v-J correlation will be qualitatively different from those when there is no correlation. 

Figure 7.9 Raw experimental Doppler profile UF data of the product state 0H(X / = 0, J = 5), for different laser light polarization directions (clockwisefrom top —45 , 0°, 45°, 90°), which are converted into 3D velodly-angle polar plots of the product scattering distribution. Information on the reaction stereodynamics can be extracted from the data. Experimentaldata adapted with permission from Brouard etal, J Phys. Chem. A106 3629. Copyright 2002 American Chemical Sodely...

Fig. 3.4 Lamb dip experiment (a) experimental arrangement (b) velocity distribution curves. Note that the saturated velocity groups can overlap only when the laser frequency is tuned to the center of the Doppler profile, (c) Power output curve. The laser intensity is plotted as a function of the laser frequency or the fine tuning of the separation between the laser mirrors. The narrow dip in the center is the Lamb dip.

There have been very few studies of the effects of non-Newtonian properties on flow patterns in hydrocyclones, although Dyakowski et al.,AU have carried out numerical simulations for power-law fluids, and these have been validated by experimental measurements in which velocity profiles were obtained by laser-doppler anemometry. 

Usually, mainly Doppler broadening determines the gain profile of a particular laser transition. Indeed, due to the different configurations achievable with gas lasers (namely, a large cavity length), the laser line can be narrower than the Doppler linewidth. Different experimental realizations of single-mode lasers are detailed elsewhere (Demtroder, 2(X)3). 

Experimental details for the cross-section measurements were presented in the literature. Briefly, after the irradiation by electron beam pulse for a few nanoseconds, the time-dependent absorption for the atomic line transition Rg Rg -i-/zv was measured to observe the time-dependent population of the excited rare gas atoms Rg. The population of excited Rg was determined using an absorption law for the atomic lines, where the broadening of the absorption profile due to the thermal Doppler effect and due to the attractive interatomic potentials was reasonably taken into consideration. The time-dependent optical emission from energy transfer products, such as ... 

Kostiuk et al. [40] measured experimentally the flow field of the vertical co-axial turbulent impinging streams with a two-component Laser Doppler velocity meter. The opposing gas streams were ejected from two burner nozzles, which were designed to produce a uniform axial velocity profile at their exits. The turbulence in the flow was generated by a perforated plate located at the end of the contraction section in each nozzle. The air velocity at the exit of the nozzle was varied from 4.1 to 11.4 m s and... 

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