Laser fields, intense

It has been shown theoretically [27] that the structural deformation of C02 most likely occurs at the doubly charged state, CO, because no significant potential deformation is identified at C02 and CO, even when the laser field intensity within an ultrashort laser pulse becomes sufficiently large for further ionization into COg and CO2, respectively. Since the adiabatic ionization potential of CS + to form CS j 1 ( 27 eV) is substantially larger than those of CS2 —s- CSj + e (10eV) and CSj —s- CS 4" + e (17eV), the observed structural deformation in the intense laser field is considered to reflect the nuclear dynamics at the doubly charged state, CS 4-, in the same manner as predicted by the theoretical calculation on the isovalent C02. 

O. Atabek, R.Lefebvre, Multiple occurrence ff zero-width resonances in photodissociation Effect of laser field intensity and frequency, Phys. Rev. A 78 (2008) 043419. 

B. Reischl, Quantum Dynamical Three-Dimensional Ab-Initio Approach to a Femtosecond Pump-Probe Ionization Spectrum of Naa (B) at Low Laser Field Intensities , Chem. Phys. Lett. 239, 173 (1995). 

R. de Vivie-Riedle and B. Reischl, Quantum Calculations of Femtosecond Pump-Probe Spectroscopy in K2 for Low Laser Field Intensities , Ber. Bun-senges. Phys. Chem. 99, 485 (1995). 

We used linearly polarized Gaussian laser pulses centered around t = 12.3 fs in the calculations. This is the value of the delay time when the mean of the intemuclear distance of the ground state wave packet vertically transferred to the ground state of the ion reaches its maximal value in the field-free case. The center wavelength is 200 nm and the two employed laser field intensity values are (1 x lO Wcm", 1 x 10 Wcm ). Several different pulse lengths given by their full width at half-maximum (FWHM) (fpuise = 10,20,30,40 and 50 fs) have been applied. 

Experiments with HCl (Park et al. 1991) have confirmed the predictions of coherent-control theory, particularly the sinusoidal dependence of the ionization rate on the relative phases of the two exciting lasers, as well as the dependence of the degree of sinusoidal modulation of the ionization cinrent on the relative laser field intensities. This technique was also used in experiments on controlfing the product ratio in the photodissociation of HI (Zhu et al. 1995) and the branching ratio in the photodissociation of Na2 (Shnitman et al. 1996). 

The difference between optical nutation and free induction decay should be clear. While the optical nutation occurs at the Rabi frequency which depends on the product of laser field intensity and transition moment, the free induction decay is monitored as a heterodyne signal at the beat frequency 0) 2 which depends on the Stark shift. The importance of these coherent transient phenomena for time-resolved sub-Doppler spectroscopy is discussed in the next section. Its application to the study of collision processes is treated in Chap.12. For more detailed information the excellent reviews of BREWER [11.43,48] are recommended. 

Such electronic excitation processes can be made very fast with sufficiently intense laser fields. For example, if one considers monochromatic excitation with a wavenumber in the UV region (60 000 cm ) and a coupling strength / he 4000 (e.g. 1 Debye in equation (A3.13.59), / 50 TW cm ),... 

Seideman T 1995 Rotational excitation and molecular alignment in intense laser fields J. Chem. Phys. 103 7887-96... 

Friedrich B and Herschbach D 1995 Alignment and trapping of molecules in intense laser fields Phys. Rev. Lett. 74 4623-6... 

Friedrich B and Herschbach D 1996 Alignment enhanced spectra of molecules in intense non-resonant laser fields Chem. Phys. Lett. 262 41... 

Figure C 1.5.10. Nonnalized fluorescence intensity correlation function for a single terrylene molecule in p-terjDhenyl at 2 K. The solid line is tire tlieoretical curve. Regions of deviation from tire long-time value of unity due to photon antibunching (the finite lifetime of tire excited singlet state), Rabi oscillations (absorjDtion-stimulated emission cycles driven by tire laser field) and photon bunching (dark periods caused by intersystem crossing to tire triplet state) are indicated. Reproduced witli pennission from Plakhotnik et al [66], adapted from [118].

Multiphoton processes are also undoubtedly involved in the photodegradation of polymers in intense laser fields, eg, using excimer lasers (13). Moreover, multiphoton excitation during pumping can become a significant loss factor in operation of dye lasers (26,27). The photochemically reactive species may or may not be capable of absorption of the individual photons which cooperate to produce multiphoton excitation, but must be capable of utilising a quantum of energy equal to that of the combined photons. Multiphoton excitation thus may be viewed as an exception to the Bunsen-Roscoe law. 

Approximating any external fields (electric or magnetic) by considering only their lineal components. For normal conditions, this will be quite a good approxunation, however, this is not the case for intense laser fields for example. 

Codling K, Frasinski LJ (1996) Molecules in Intense Laser Fields an Experimental Viewpoint. 86 1-26... 

Kulander KC, Schafer KJ (1996) Time-Dependent Calculations of Electron and Photon Emission from an Atom in an Intense Laser Field 86 149-172 Kiinzel FM, see Buchler JW (1995) 84 1-70 Kurad D, see also Tytko KH (1999) 93 1-64 Kustin K, see Epstein IR (1984) 56 1-33... 

Numerical examples are shown in Figs. 7-9. The model system used is a 2D model of H2O in a continuous wave (CW) laser field of wavelength 515nm and intensity lO W/cm. The ground electronic state X and the first excited state A are considered. The bending and rotational motions are neglected for... 

T. Brabec and F. Krausz, Intense few-cycle laser fields frontiers of nonlinear optics, Rev. Mod. Phys. 72, 545 (2000). 

Note that parameters ft and 5 depend on signal amplifications in the utilized detectors and on the elements in the optical path (optical filter, spectral detection bands) only, while a and y are additionally influenced by relative excitation intensity. This is usually a fixed constant in wide-field microscopy but in confocal imaging laser line intensities are adjusted independently. Furthermore, note that the a factor equals 5 multiplied by y (see Appendix for further detail). 

Proceedings Atoms, Solids and Plasmas in Super-Intense Laser Fields... 

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