Laser pulse-induced properties

The SSEA, which is the subject of this review, was introduced in 1993-1994 with the purpose of exploring the potential and the efficiency of using state-specific wavefunctions in solving from first principles TDMEPs related to laser pulse-induced properties and phenomena. In a large number of applications since then, it has been demonstrated that this fundamental, yet conceptually simple, approach to such TDMEPs can indeed be realized computationally. 

The Chapter by N. Garcia, V. Climent and J. Feliu provides a lucid and authoritative overview of the use of laser-pulsed induced temperature variations at the platinum single-ciystal/aqueous solution interphases and of the rigorous analysis of these experiments via Gibbs thermodynamics to extract new and very valuable information on the stracture and reactivity of the metal/solution interphase. The authors show how some key interfacial properties can be evaluated directly via this elegant analysis, such as the entropy of charge-transfer adsoibed species, the entropy of formation of the interfacial water network and the potential of water reorientation. 

Nonlinear Optical Properties. For many optical signal processing applications, it is desirable for materials to have large optical nonlinearities and fast response times. For example, third-order nonlinear optical properties (qv) result in laser-pulse-induced refractive index changes that occur on the femtosecond... 

In the following, we will discuss two basic - and in a sense complementary [44] - physical mechanisms to exert efficient control on the strong-field-induced coherent electron dynamics. In the first scenario, SPODS is implemented by a sequence of ultrashort laser pulses (discrete temporal phase jumps), whereas the second scenario utilizes a single chirped pulse (continuous phase variations) to exert control on the dressed state populations. Both mechanisms have distinct properties with respect to multistate excitations such as those discussed in Section 6.3.3. 

The first volume contained nine state-of-the-art chapters on fundamental aspects, on formalism, and on a variety of applications. The various discussions employ both stationary and time-dependent frameworks, with Hermitian and non-Hermitian Hamiltonian constructions. A variety of formal and computational results address themes from quantum and statistical mechanics to the detailed analysis of time evolution of material or photon wave packets, from the difficult problem of combining advanced many-electron methods with properties of field-free and field-induced resonances to the dynamics of molecular processes and coherence effects in strong electromagnetic fields and strong laser pulses, from portrayals of novel phase space approaches of quantum reactive scattering to aspects of recent developments related to quantum information processing. 

A ruby laser pulsed irradiation of Ge/Si heterostructures with Ge nanoclusters (quantum dots) at the irradiation energy density near the melting threshold of Si surface has been studied by means of Raman spectroscopy and by numerical simulation of the laser-induced processes. Two types of the structures have been tested. They differ mainly in the depth of nanoclusters occurence (0.15 and 0.3 pm). From the RS analysis one may conclude that laser irradiation results in different changes of QD properties. The decrease of QD size dispersion is observed in the samples with QDs at 0.3 pm, this effect is not observed in the samples with QDs at 0.15 pm. The numerical simulation of laser heating shows that the QDs are in a molten state for the same time, but the induced temperatures of nanoclusters for the two depths differ by -100 K. This result indicates that qualitatively different effects of the laser irradiation may be connected with different temperatures of QDs during laser irradiation. 

The superiority of using lasers for material studies often lies in its spatial and temporal flexibilities, that is, the material can selectively excited and probed in space and time. These qualities may allow us to elucidate fundamental material properties not accessible to conventional techniques. The location, dimension, direction, and duration of the material excitation can be readily controlled through adjustment of the beam spot, direction, polarization, and pulse width of the exciting laser field. The flexibilities can be further enhanced when two or more light waves are used to induce excitations. Such a technique, however, has not yet been fully explored in liquid-crystal research. Although the recent studies of optical-field-induced molecular reorientation in nematic liquid-crystal films have demonstrated the ability of the technique to resolve spatial variation of excitations, corresponding transient phenomena induced by pulsed optical fields have not yet been reported in the literature. Because of the possibility of using lasers to induce excitations on a very short time scale, such studies could provide rare opportunities to test the applicability of the continuum theory in the extreme cases. 

Generally speaking, excitation of a medium by short laser pulses can be used to study dynamic properties of the medium over a very wide time range. Here, we have shown that nanosecond-pulse excitation can yield information about the dynamics of molecular reorientation on the -10-sec time scale, and thermal effect on the 10—l(X)-msec time scale. The power of this technique lies in the fact that a single 6-function-like laser pulse may induce a number of fundamental excitation modes of vastly different time constants. Consider, for example, molecular reorientation coupled with flow induct by a picosecond laser pulse in a liquid crystal. It can be shown that, aside from the thermal effect, the transient behavior will manifest itself with three characteristic time constants ... 

In Sect. 3.1.1, for a similar system, the model molecule K2 excited to its A state, the wave packet propagation is explored in greater detail by real-time three-photon ionization (3PI) spectroscopy. Applying laser pulses of moderate intensities allows the selective detection of the pure vibrations of the A state, in excellent agreement with quantum dynamical calculations [42]. Both the favorable spectroscopic properties of K2 and the special molecular dynamics induced by the selected moderate laser intensity combine to open... 

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