Laser parameters

The quantities in this fomuila are defined as in equation Bl.5,32. but with the laser parameters translated into more convenient tenns is the average power at the indicated frequency is the laser pulse duration ... 

Once the mechanisms of dynamic processes are understood, it becomes possible to think about controlling them so that we can make desirable processes to occur more efficiently. Especially when we use a laser field, nonadiabatic transitions are induced among the so-called dressed states and we can control the transitions among them by appropriately designing the laser parameters [33 1]. The dressed states mean molecular potential energy curves shifted up or down by the amount of photon energy. Even the ordinary type of photoexcitation can be... 

The laser parameters should be chosen so that a and p can make the nonadiabatic transition probability V as close to unity as possible. Figure 34 depicts the probability P 2 as a function of a and p. There are some areas in which the probabilty is larger than 0.9, such as those around (ot= 1.20, p = 0.85), (ot = 0.53, p = 2.40), (a = 0.38, p = 3.31), and so on. Due to the coordinate dependence of the potential difference A(x) and the transition dipole moment p(x), it is generally impossible to achieve perfect excitation of the wave packet by a single quadratically chirped laser pulse. However, a very high efficiency of the population transfer is possible without significant deformation of the shape of the wave packet, if we locate the wave packet parameters inside one of these islands. The biggest, thus the most useful island, is around ot = 1.20, p = 0.85. The transition probability P 2 is > 0.9, if... 

Figure 39. Pump-dump control of NaK molecule by using two quadratically chirped pulses. The initial state taken as the ground vibrational eigenstate of the ground state X is excited by a quadratically chirped pulse to the excited state A. This excited wavepacket is dumped at the outer turning point at t 230 fs by the second quadratically chirped pulse. The laser parameters used are = 2.75(1.972) X 10-2 eVfs- 1.441(1.031) eV, and / = 0.15(0.10)TWcm-2 for the first (second) pulse. The two pulses are centered at t = 14.5 fs and t2 = 235.8 fs, respectively. Both of them have a temporal width i = 20 fs. (See color insert.) Taken from Ref. [37].

MeV required in proton-therapy for an effective treatment of deep seated tumors [26]. Fuchs and co-authors have proposed a scaling law [27], allowing the necessary laser parameters to produce proton beams of interest for such applications to be estimated. In their work, best suited to hundreds of fs/some ps duration laser pulses, they use the self-similar fluid model proposed by Mora [28] giving the following estimate for the maximum FWD proton energy ... 

As a consequence, the optimal thickness Lopt introduced above corresponds, for a given set of laser parameters (pulse duration and intensity, contrast ratio, and pre-pulse duration), to the thickness, allowing the perturbations due to the pre-pulse from the front surface, which travel at typical... 

Thin-film platinum silicide, 19 632 Thin-film shape, laser parameters and,... 

The results are shown in Fig. 3 and Table I. Apparently, optimal IR femtosecond/picosecond laser pulses with durations tp = 500 fs may induce nearly perfect transitions (12), (13) in the model OH. Similar examples are documented in Refs. 13, 18, and 23. A detailed discussion of the derivation of the optimal laser parameters, depending on the vibrational level Ev and the transition dipole matrix elements nvw, is also given in Refs. 13, 18, and 23. Suffice it here to say that in many (but not all) cases the optimal frequency is close (but not identical) to the resonance frequency,... 

Laser Parameters for Vibrational Transitions in Model Systems OH and SBV... 

The first reported laser action in rare earth complexes was obtained by Lempicki and Samelson [656] for europium benzoylacetonate in alcoholic solution. The laser parameters for this complex have also been evaluated by Lempicki and coworkers [656, 660] who found a slightly better quantum efficiency (0.8) for europium benzoylacetonate than for ruby (0.7), the solid state laser. The laser action of europium benzoylacetonate has also been investigated by Schimitschek [661] and Bhatjmik et al. [662]. Some other complexes of Eu3+ viz. dibenzoylmethide [665,664], m-4,4,4-trifluoro-l(2-thienyl)-l,3-butanedione [665], thenoyl-trifluoroacetonate [666, 667] were also found to lase. 

Figure 1.7 Surface quality of a stainless steel microchannel foil machined by laser ablation. The laser parameters have been incorrectly set.

Detection limits for most reported LA-ICP-MS studies have been near 1 xg/g, although these limits are very dependent on the element, sample type, laser system, laser parameters, pit size, and ICP-MS used. Detection limits in the 1- to... 

The paper is organized as follows Section 2.2 briefly reviews the effect of the laser parameters. Section 2.3 describes the experimental methods and setups used in our group. Section 2.4 outlines our results regarding isomer ionization, wavelength effects, resonance mechanism, electron recollision, and excitation pulse width dependence. Section 2.5 describes FLMS including our recent application to dioxins and femtosecond time-of-flight (TOF) mass spectra are compared with those by electron impact excitation. Finally the contents of the paper are summarized in Sect. 2.6. 

Fig. 5.7. Pump-dump control of NaK molecule using two quadratically chirped pulses. The initial state is taken as the ground vibrational eigenfunction of the ground state X1S+ and this is excited by a quadratically chirped pulse to the excited state A1E+. The excited wavepacket is dumped at the outer turning point t cs 230 fs by the second quadratically chirped pulse. The laser parameters used are...

Since the classical treatment has its restrictions and the applicability of the quantum OCT is limited to low-dimensional systems due to its formidable computational cost, it would be very desirable to incorporate the semiclassical method of wavepacket propagation like the Herman-Kluk method [20,21] into the OCT. Recently, semiclassical bichromatic coherent control has been demonstrated for a large molecule [22] by directly calculating the percent reactant as a function of laser parameters. This approach, however, is not an optimal control. 

Fig. 8.14 Control over dimethylallene enantiomer populations as a function of the detuning A] for various laser powers. First column corresponds to probabilities of L (dot-dash curves) and D (solid curves) after a single laser pulse, assuming that the initial state is all L. Second column is similar, but for an initial state that is all D. Rightmost column corresponds to the . probabilities L and D after repeated excitation-relaxation cycles, as described in the text. First fqw corresponds to control using laser parameters on the extreme right, in which there is no internal conversion second row uses the same laser parameters as does the first row, but with internal conversion time of 10 ps bottom row shows results for an internal conversion time mf 10ps, but with modified laser parameters shown.

All of the quantum control scenarios involve a host of laser and system parameters. To obtain maximal control in any scenario necessitates a means of tuning the system and laser parameters to optimally achieve the desired objective. This topic, optimal control, is introduced and discussed in Chapters 4 and 13. The role of quantum interference effects in optimal control are discussed as well, providing a uniform picture of control via optimal pulse shaping and coherent control. 

Fig. 2. Muonium Is-2s signal [14]. The solid squares represent the theoretical expectations based on measured laser parameters and our theory [19]...

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