Femtosecond light pulse

By making use of classical or quantum-mechanical interferences, one can use light to control the temporal evolution of nuclear wavepackets in crystals. An appropriately timed sequence of femtosecond light pulses can selectively excite a vibrational mode. The ultimate goal of such optical control is to prepare an extremely nonequilibrium vibrational state in crystals and to drive it into a novel structural and electromagnetic phase. 

The possibility of reflection of electrons by an evanescent wave formed upon the total internal reflection of femtosecond light pulses from a dielectric-vacuum interface is quite realistic. The duration of the reflected electron pulses may be as long as 100 fs. In the case of electrons reflecting from a curved evanescent wave, one can simultaneously control the duration of the reflected electron pulse and affect its focusing (Fig. lc). Of course, one can imagine many other schemes for controlling the motion of electrons, as is now the case with resonant laser radiation of moderate intensity [9, 10]. In other words, one can think of the possibility of developing femtosecond laser-induced electron optics. Such ultrashort electron pulses may possibly find application in studies into the molecular dynamics of chemical reactions [1,2]. 

S. Skupin, L. Berge, U. Peschel, F. Lederer, G. Mejean, J. Yu, J. Kasparian, E. Salmon, J. P. Wolf, M. Rodriguez, L. Woste, R. Bourayou, R. Sauerbrey, Filamentation of femtosecond light pulses in the air Turbulent cells versus long-range clusters, Physical Review E 70, 046602 (2004)... 

Research has also been devoted to cationic two-photon photopolymerization using conventional initiator systems such as isopropylthioxanthone (ITX)/diaryl iodonium salt, with ITX serving as the photo sensitizer [45, 46]. Mode-locked operated Ti sapphire laser systems emitting femtosecond light pulses at 600, 710, or 795 nm were employed in these studies. 

T. Baumert, R. Thcdweiser, V. Weifi, and G. Gerber, Time-Resolved Studies of Neutral and Ionized Nan Clusters with Femtosecond Light Pulses , Z. Phys. D 26, 131 (1993). 

B. Wilhelmi, Propagation of Femtosecond Light Pulses Through Dye Amplifiers in Dye Lasers 25 Years, Vol. 70 Topics in Applied Physics, M. Stuke (ed.) (Springer, Berlin, Heidelberg, 1992), p 111. 

M. BeUini, A. Bartoli, T.W. Hansch Two-photon Fourier spectroscopy with femtosecond light pulses. Opt. Lett. 22, 540 (1997)... 

The const value depends on the shape of the pulse envelope. For the Gauss pulse const = 0.44. The pulse with a duration of 10 s has a spectral width of 1100 cm. This implies that the femtosecond light pulse can simultaneously excite several vibrational states. 

Thus, femtosecond light pulses allow one to provide the high time resolution, create nonstationary quantum states, form highly excited molecules, influence on PES, and generate ultrashort light, electron, and X-ray pulses. 

This reaction is a non-adiabatic process. The potential curves for the Nal molecule are shown in Fig. 4.7. It is seen that there is a pseudo-crossing between the curves of the excited covalent state and ionic ground electronic state. The femtosecond light pulse forms the coherent nuclear wave package in the excited electronic state. We mentioned above that the intramolecular dynamics could be interpreted... 

The nonradiative transitions in pyridine vapor have been studied using femtosecond, time-resolved mass spectroscopy. In these experiments, pyridine vapor was excited with a femtosecond light pulse of 277 nm, which is below (-300 cm ) the channel three threshold. Time-resolved mass spectroscopy revealed a fast decay component of 400 fs, which describes the initial motion on the pyridine potential surface and shows components of 3.5 and 15 ps, which were assigned to the formation of Dewar-pyridine 112 and azabenzvalene 111, respectively (Scheme 28). ... 

These processes have also been studied using ultra-fast electron diffraction. In this case, a femtosecond light pulse of 267 nm was used to excite pyridine 109 vapor into the S, (n, n ) state with an excess energy of -2700 cm, well above the -1600 cm threshold for channel three behavior. Sequentially delayed ultra-short electron pulses were then used to probe the ensuing structural dynamics. 

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