Laser velocity-selective control

The laser control of the velocity distribution of atoms or molecules at particular quantum levels that emerged in the course of development of saturation spectroscopy free of Doppler broadening (Lamb 1964) is fairly close to the ideas considered in this book. I myself started to work on the problem of laser elimination of Doppler broadening as far back as 1965 and gradually progressed to ideas of laser confinement of atomic motion within a volume of about A . Therefore, I have decided to include a brief description of the ideas of laser velocity-selective control of atoms and molecules. 

As we pointed out above, an attractive feature of the velocity selected K collisions is that we can examine the region o) 2n < 1/r. We consider first the case in which there is no control over the phase of the field at which the collisions occur. This case is exemplified by Figs. 15.11(b)-(d), which show the effect of adding progressively larger amplitude 1 MHz rf fields of uncontrolled phase. Since the laser fires at an uncontrolled phase of the rf field, the observed cross section can be calculated using Eq. (15.34). As shown by Fig. 15.11 the cross section is broadened in approximately the manner shown in Fig. 15.7. As shown by a... 

The two extreme cases cu 1/r and cu -C 1/t are easily understood, but in very different terms, so it is less clear how to think about the case w 1/r. Nonetheless, the low frequency regime suggests that the phase of the rf field relative to when the collision occurs is likely to be important. To control this phase we use transform limited collisions of /C atoms in a velocity selected beam so that we know when the collisions begin and end, and we synchronize the rf field to the laser pulse initiating the collisions [Renn 1991], Specifically, we have studied the process of Eq. (10) in rf fields phase locked to the collisions. 

V.S. Letokhov Laser control of atomic motion Velocity selection, cooling and trapping. Comments At. Mol. Phys. 6, 119 (1977)... 

The PIV techniques provide instantaneous velocity field information. The spatial and temporal resolution of PIV can be controlled with proper selection of lighting source, i.e., laser imaging system, i.e., camera and fi ame grabber, and optical arrangements/compo-nents. The continuous development of this hardware in the near future is expected to result in very high spatial and temporal resolution velocity measurements. Therefore, the p-PIV and p-holographic PIV techniques will develop as high-resolution indirect instantaneous shear stress measurement techniques in the near future. 

Laser SNMS requires the operation with properly selected duty cycles that control the delay times between the primary ion pulse, a pulsed extraction voltage for separating the secondary ions from post-ionized neutrals, and the firing of the postionizing laser pulse. Such duty cycles have, in addition, to be synchronized with the stepwise motion of the pulsed primary ion beam across the sample surface in the microprobe mode of laser SNMS. The selection of appropriate duration and decay times of the ion and laser pulses, of the laser intensity, and beam shape is important to make the photoion yields independent on the sputtered particle velocities. The detection volume must be matched to the entrance ion optics of the TOP such that it becomes independent of the individual ionization process. Usually, laser intensities in the range from 10 to lO Wcm are applied. While the particle density in the detection volume is monitored at small laser intensities, the particle flux is measured at high photon densities. 

It is this group of particles that can be selectively excited to the upper state. This possibility forms the basis for the laser control of the velocity distribution of particles at desired quantum levels. 

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