Partially coherent laser

COUNTERING PARTIALLY COHERENT LASER EFFECTS IN PUMP-DUMP CONTROL... 

Equations (3.19) and (5.27) represent two extremes, where the result is eitfc fully coherent or fully incoherent. It is enlightening to consider [188] the effeqf partially coherent laser sources through the example of the pump-dump scenario]) Section 3.5 in the case where the laser is not fully coherent. 

We adopt a modified-phase diffusion model for the partially coherent laser source in which the phase SA is allowed to be time dependent and random. Thus, the molecule-laser interaction is modeled by the interaction with an ensemble of lasers, each of different phase. This ensemble is described by a Gaussian correlation for the stochastic phases with a decorrelation time scale rxc ... 

Pt(l 11) [6-8], Cu(l 1 1) [9] and Ag(l 1 1) [9], and CO fromPt(00 1) [10] andPt(l 1 1) [11,12]. On the other hand, these molecules are not desorbed from Ni and Pd metal surfaces in spite of the isoelectronic character of the metals Ni, Pd and Pt [13,14]. Desorption induced by subpicosecond-pulsed laser takes place via multiple correlated (and partially coherent) electronic transitions DIMET. DIMET is a very different mechanism from DIET [15-17] and in DIMET the vibrational excitation during the multiple electronic transitions leads to the desorption. Desorption via multiple vibrational transitions has also been observed using an infrared laser [18]. However, these topics are not described in this review. 

In laser Doppler velocimetry (LDV) [1] based on the differential technique, two coherent laser beams, which are usually generated by beam splitting, are made to intersect at a small angle 26, see Fig. 1. In the area of intersection (the measurement volume), an interference fringe pattern with nearly parallel planes arises. The normal vector of these planes lies in the plane spanned by the LDV partial beams and is aligned... 

Ophthalmology. A laser interferometry technique using infrared light for measuring intraocular distances (eye length) is widely used in ophthalmology. This technique has been developed and marketed primarily by Zeiss, which sells an instrument called the lOL Master. The technique is also referred to as partial coherence interferometry (PCI) and laser Doppler interferometry (LDl) and is an area of active research for other biological apphcations. 

A flash lamp encircles a ruby rod. Light of 545 nm (green) from the flash"pumps"electrons from level 1 to level 3,then level 2, from which stimulated emission forms a laser pulse at 694 nm (red).The stimulated emission bounces back and forth between reflective surfaces at the ends of the ruby rod, building up a coherent laser beam. One end has a partially reflective surface to allow the laser beam to exit from the ruby. 

Since partial laser phase coherence affects both the direct terms as well as the cross terms, the extent of control is dependent on the laser properties through the relative magnitudes of ( l( ulg) (c02g))l and (l i-(w ) 2)> =1,2. To expose the dependence on the coherence of the pump field denote the terms ckc jF u>jk)dq kj)(E) by a ]- and consider the ratio of the k / j term in Eq. (5.44) to the associated diagonal terms. That is, consider the contrast ratio ... 

Numerical studies [193] show that Eq. (5.54) provides a zeroth-order approxima-" tfon to the results of a full computation, which underestimates the degree of possible control in a realistic system. In addition, these results show that even for phase f tpfusion fields, which have widths on the order of wavenumbers, control is still - msive (e.g., Co 5). Examination of the experimental results on one-photon vs. 1-e-photon control show, however, contrast ratios on the order of 30% [76, 194], Tjhat is, the main experimental limitation, thus far, is due to experimental issues other (rihe partial laser coherence. 

O Some of the laser s coherent light passes through the partially transparent mirror at one end of the tube and exits the laser. These photons make up the light emitted by the laser. 

FIGURE 22.24 (a) In this solid-state laser, photons emitted as electrons and holes recombine to stimulate the emission of additional photons, (b) Reflection by a mirror on the right side sends coherent waves back through the laser medium, (c) Further amplification occurs by stimulated emission, (d) Some of the waves pass through a partially reflecting mirror on the left side. 

Amirav and Jortner29 did make an attempt to redefine N, the number of states coupled, to JVeff, the dilution factor, which can be used when Lahmani et al. s5 conditions are not fulfilled. It should then also be equal to A+/A, but their treatment takes only partially into account the effect of the coherence width of the laser. This Neff arose from their consideration of the quantum yield and its dependence on J. In Section V we will discuss the quantum yield of the J = 0, K = 0 state, while in Section VI we consider its J dependence. 

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