Doppler distribution

The electric fields from all j transitions can be detected simultaneously by mixing them with a local oscillator at frequency wlo having a fixed phase relationship to wp, and integrating over the Doppler distribution (when necessary). The resultant signal is... 

Our studies of the effect of velocity-changing collisions in an rf-laser double resonance experiment contribute to a new vista into the role of collisictis in laser spectroscopy of sub-level structures the limitation of the observation time of the active atoms due to narrow-bandwidth optical excitation and simultaneous velocity diffusion can be of importance for a variety of spectroscopic techniques that use a velocity-selective excitation and detection of either sublevel populations or sublevel coherence. On the other hand, the collisional velocity diffusion of sublevel coherence within an optical Doppler distribution can also give rise to new and surprising phenomena as will discussed in the next section. 

Fig. 5.a) Experimental scheme EOM, electrooptic modulator B, static tranverse magnetic field X/4, retardation plate inserted with one of its main axes parallel to the polarization of the probe field , polarization analyzer PD, photodetector, b) Modulated excitation process of Zeeman coherence for the Zeeman-split J=1-J =0 transition of Sm. c) Detection process showing the induced Raman sidebands, d) Schematic of the Doppler distribution indicating the velocity selectivity of the optical excitation and detection of sublevel coherence. 

Ramsey s method for the observation of narrow radiofre-guency (rf) resonances is well known from atomic and molecular beam experiments . In this contribution, we demonstrate the occurence of similar Ramsey resonances in an atomic vapor due to collisional velocity diffusion of sublevel coherence within an optical Doppler distribution. This new phenomenon is observed using coherent resonance Raman processes to optically induce and detect Zeeman coherence in the Sm A=570.7 nm J=1-J =0 transition. 

Fig. 3 shows I uj) for a = 0.3 and the Doppler distribution with a thermal velocity increased by AVq. One can see that these distributions are quite close to each other. 

Fig. 3. Absorption line shape for

Figure B2.5.12 shows the energy-level scheme of the fine structure and hyperfme structure levels of iodine. The corresponding absorption spectrum shows six sharp hyperfme structure transitions. The experimental resolution is sufficient to detennine the Doppler line shape associated with the velocity distribution of the I atoms produced in the reaction. In this way, one can detennine either the temperature in an oven—as shown in Figure B2.5.12 —or the primary translational energy distribution of I atoms produced in photolysis, equation B2.5.35.

Defining the z-axis as the direction of propagation of the light s photons and carrying out the averaging of the Doppler factor over such a velocity distribution, one obtains ... 

Doppler broadening arises from the random thermal agitation of the active systems, each of which, in its own test frame, sees the appHed light field at a different frequency. When averaged over a Maxwellian velocity distribution, ie, assuming noninteracting species in thermal equilibrium, this yields a line width (fwhm) in cm C... 

Hollow Sprays. Most atomizers that impart swid to the Hquid tend to produce a cone-shaped hoUow spray. Although swid atomizers can produce varying degrees of hoUowness in the spray pattern, they aU seem to exhibit similar spray dynamic features. For example, detailed measurements made with simplex, duplex, dual-orifice, and pure airblast atomizers show similar dynamic stmctures in radial distributions of mean droplet diameter, velocity, and Hquid volume flux. Extensive studies have been made (30,31) on the spray dynamics associated with pressure swid atomizers. Based on these studies, some common features were observed. Test results obtained from a pressure swid atomizer spray could be used to iUustrate typical dynamic stmctures in hoUow sprays. The measurements were made using a phase Doppler spray analyzer. 

The temperature dependence of sod is related to that of the recoil-free fraction /(T) = Qxp[— x )Ey / Hc) ], where (x ) is the mean square displacement (2.14). Both quantities, (x ) and can be derived from the Debye model for the energy distribution of phonons in a solid (see Sect. 2.4). The second-order Doppler shift is thereby given as [20]... 

Fig. 1. Schematic illustration of the basic concept of the Doppler-selected TOF technique. The hatched slice on the left represents a Doppler-selection of a given vz- The strip on the Doppler slice (the middle figure) is the ID Vy-distribution measured under the -restriction of a slit in front of the TOF spectrometer. The combination of many Doppler-selected TOF measurements yields the result shown on the right. The lower figures are the corresponding actual data at each stage for the reaction of S(1D) + H2.

To implement the Doppler-selected TOF measurement, the initial relative velocity is arranged to be parallel to the propagation vector of the probe laser. This critical configuration can readily be achieved in this rotating sources machine.36 Under this configuration, each Doppler-sliced 2D distribution exhibits a cylindrical symmetry The slit in front of the TOF spectrometer allows only those products with a rather small vx to be detected. Hence, only the -distribution, obtained by the TOF measurement, is needed to completely characterize the Doppler-sliced 2D (vx — vy) distribution. 

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