Femtosecond pump-probe

Femtosecond pump-probe experiments have burgeoned in the last ten years, and this field is now connnonly referred to as laser femtochemistry [26, 27, 28 and 22],... 

Pollard W T, Lee S-Y and Mathies R A 1990 Wavepacket theory of dynamic absorption spectra in femtosecond pump-probe experiments J. Chem. Phys. 92 4012... 

It is interesting to note that the use of correlation functions in spectroscopy is an old topic, and has been used to derive, for example, infrared (IR) spectra, from classical trajectories [134,135]. Stock and Miller have recently extended this approach, and derived expressions for obtaining electronic and femtosecond pump-probe spectra from classical trajectories [136]. 

Nechay, B.A., Siegner, U.,Achermann, M., Bielefeldt, H. and Keller, U. (1999) Femtosecond pump-probe near-field optical microscopy. Rev. Sci. Instrum., 70, 2758-2764. 

The results for the A state show that a different mechanism is operative. A series of femtosecond pump-probe experiments were performed at wavelengths corresponding to the Rydberg states A (v = 0,1,2) of ammonia molecules.64-66,68,69 The wavelengths used to access these vibrational levels were 214 nm, 211 nm, and 208 nm for the pump laser and 321 nm, 316.5 nm, and 312 nm for the probe laser, respectively. 

Fig. 7 Femtosecond pump-probe data for TD 2765 (molecular structure shown left). The probe wavelength is set at 670 nm and the pump wavelengths are (1) 710 nm, (2) 700 nm, and (3) 690 nm. See [62] for additional details...

Describing complex wave-packet motion on the two coupled potential energy surfaces, this quantity is also of interest since it can be monitored in femtosecond pump-probe experiments [163]. In fact, it has been shown in Ref. 126 employing again the quasi-classical approximation (104) that the time-and frequency-resolved stimulated emission spectrum is nicely reproduced by the PO calculation. Hence vibronic POs may provide a clear and physically appealing interpretation of femtosecond experiments reflecting coherent electron transfer. We note that POs have also been used in semiclassical trace formulas to calculate spectral response functions [3]. 

Importantly, Cl s seems to be involved in many classes of physical, chemical and biological processes, from pericyclic reactions to the complex light harvesting and energy conversion functions of chromophores in proteins (See in this volume) and others amply described in this conference. In contrast, direct experimental information on the passage of the vibrational wavepacket through or near Cl s is less abundant. It mostly concerns, femtosecond pump-probe experiments on isolated organic molecules in the gas phase. 

Following another experimental approach, GWgoire et al [9] have tried to understand the influence of an increasing number of solvent molecules on the femtosecond dynamics of diatomic molecules, including the dimers Nal and Csl. Due to its relative simplicity, the isolated Nal molecule has been studied extensively with pump-probe techniques both experimentally [10], and theoretically [11,12], In this report, we investigate theoretically the femtosecond pump-probe ionization of Nal and Csl when aggregated with a molecule of acetonitrile CH3CN. 

Experimentally it has proven very difficult to investigate bimolecular reaction kinetics. Although optical techniques have been developed with femtosecond time resolution, the bimolecular nature of the reactions precludes standard femtosecond pump-probe experiments, as a common starting time for the reaction is not readily established. Here we initiate the fast bimolecular acid-base reaction by converting a very weak base, NO3 to a weak base ONOO" and follow the reaction ONOO + H+ as a function of [ft]. 

A simple approach for the calculation of femtosecond pump-probe spectra for electronically nonadiabatic systems... 

Femtosecond pump-probe investigation of primary photoinduced processes in C60/Sn nanostructures... 

A simple approach lor the calculation of Femtosecond pump-probe spectra for electronically nonndiiihuuc systems... 

G. Gerber At moderate laser intensities we do see in femtosecond pump-probe experiments a very similar slow time and long time dynamics in all cluster sizes n > 5 up to n = 50 (largest size investigated up to now) irrespective of the charge state of the particular Hg cluster. From single-pulse TOF mass spectrometry we infer that the... 

There are three quite distinct perturbations that could have caused the vibrational motion to delocalize. The first is that the potential that governs the vibrational motion is not harmonic and it is not harmonic either in the simulations or, of course, in the real molecule. In our experience, under most circumstances this is the effect that comes in at the earliest times. We have seen this to be the case not only for a chemical reaction but also in simulations of femtosecond pump-probe experi-... 

The wavepacket calculation for the femtosecond pump-probe experiment presented in Fig. 16 (bottom) is the result of the first consistent ab initio treatment for three coupled potential-energy surfaces in the complete three-dimensional vibrational space of the Naa molecule. In order to simulate the experimental femtosecond ion signal, the experimental pulse parameters were used duration A/fWhm = 120 fs, intensity I - 520 MW/cm2, and central... 

Ellington et al.40) used femtosecond pump-probe spectroscopy to probe directly the arrival of electrons injected into the TiOz film with near- and mid-IR that probe the absorption at 1.52 jum and in the range of 4.1-7.0 jUm. Their measurements indicate an instrument limited 50 fsec upper limit on the electron injection time. These observations suggest that electron injection from Dye 2 to... 

Ultrafast molecular elimination of iodine from IF2C-CF2I has been studied using the velocity map ion imaging technique in combination with femtosecond pump-probe laser excitation.51 By varying the femtosecond delay between pump and probe pulse, it has been found that elimination of molecular iodine is a concerted process, although the two carbon-iodine bonds are not broken synchronously. 

Fig. 16.1. (a) Schematic illustration of a femtosecond pump-probe experiment. The pump laser with wavelength Ai excites the molecule from the ground-state potential Vo to an excited state-potential V. After a delay r the probe laser with wavelength A2 excites the transient molecule to a second excited-state potential V2. (b) Absorption signal of the transient molecule if the wavelength of the probe laser is tuned to the asymptotic wavelength Ag0 (upper part) or to a wavelength shifted to the red of Ag0 (lower part). Reproduced from Zewail (1988). 

Baumert, T., Engel, V., Rottgermann, C., Strunz, W.T., and Gerber, G. (1992). Femtosecond pump-probe study of the spreading and recurrence of a vibrational wave packet in Na2, Chem. Phys. Lett. 191, 639-644. 

Krause, J.L., Shapiro, M., and Bersohn, R. (1991). Derivation of femtosecond pump-probe dissociation transients from frequency resolved data, J. Chem. Phys. 94, 5499-5507. 

Stock, G. and Domcke, W. (1990). Theory of femtosecond pump-probe spectroscopy of ultrafast internal conversion processes in polyatomic molecules, J. Opt. Soc. Am. B 7, 1971. 

In Eq. (4), one can see that there are two terms that depend on the space-phase factor. Eq. (5) clearly shows this situation coherence is generated between the two molecules. This coherent excitation can be called as inter-molecular coherence. This type of coherent excitation can be seen in femtosecond pump-probe non-linear coherent optical scattering spectroscopy. This chapter shall only focus on ultrafast radiationless transition as well as the dynamics of the intramolecular coherence and its relaxation. 

The effects of the vibronic coupling competing with vibrational and/or vibronic relaxation on the femtosecond pump-probe stimulated emission spectra of molecules in condensed phases have been investigated. Taking into account vibronic and vibrational relaxation and vibronic coupling in molecular terms, the coupled master equations have been briefly derived for... 

In order to apply these equations to a femtosecond pump-probe experiment, an additional assumption has to be made regarding the shape of the time resolved signal. We wish to account for the finite relaxation time of the transient polarisation and so the signal must be described by a double convolution of an exponential decay function with the pump and probe intensity envelope functions. We will assume a Gaussian peak shape so that the convolution may be calculated analytically. As we will see, the experimental results require two such contributions, and hence, the following function will be used to fit the experimental data... 

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