Femtosecond resolution

A. Rousse, C. Rischel, S. Fourmaux, I. Uschmann, S. Sebban, G. Grillon, P. Balcou, E. Forster, J. P. Geindre, P. Audebert, J. C. Gauthier, and D. HuUn, Nonthermal melting in semiconductors measured at femtosecond resolution. Nature 410, 65-68 (2001). 

Recently, a systematic experimental study has clearly proved the effect on a gaseous medium of both ASE and picosecond pedestal prior to the arrival of the ultrashort intense laser pulse [26]. The study has been based on sequences of electron density maps obtained from optical interferograms with femtosecond resolution and has been supported by numerical simulation of the ionization of the medium. 

Rousse A, Rischel C, Eourmaux S, Uschmann I, Sebban S, Grillon G, Balcou Ph, Eorster E, Geindre JP, Audebert P, Gauthier JC, Hulin D (2001) Non-thermal melting in semiconductors measured at femtosecond resolution. Nature 410 65-68... 

A. H. Zewail, Transient Species at Femtosecond Resolution, Proc. Robert A. Welch Found. Conf. Chem. Res. 1994, 38, 129. 

After the introduction of frequency resolved CARS by Maker and Terhune [1], time resolved experiments became possible with the invention of high power lasers with femtosecond resolution. Leonhardt [2] and for example Hayden [3] performed femtosecond CARS experiments in liquids. A first femtosecond time resolved CARS experiment in gas phase was performed by Motzkus et. al. [4] where the wave packet dynamics of the dissociation of Nal was monitored. The first observation of wave packet dynamics in gaseous iodine was reported by Schmitt et al. [5]. They were able to observe dynamics in both, the ground and excited state with the same experiment. A summary of high resolution spectroscopy in gas phase by nonlinear methods is given by Lang et al. [6]. 

Figure 1. Schematic indicating the different phases studied with femtosecond resolution and the area of control studied by spatial (r >, temporal (/ ), phase ( ), or potential-energy (V ) manipulation.

Recently, we reported observations of the femtosecond dynamics of tautomerization in model base pairs (7-azaindole dimers) containing two hydrogen bonds. Because of the femtosecond resolution of proton motions, we were able to examine the cooperativity of formation of the tautomer (in... 

NSOM Dynamics Imaging—Millisecond to Femtosecond Resolution... 

On the experimental side, the chemical dynamics on the state-to-state level is being studied via molecular-beam and laser techniques [2]. Alternative, and complementary, techniques have been developed in order to study the real-time evolution of elementary reactions [3]. Thus, the time resolution in the observation of chemical reactions has increased dramatically over the last decades. The race against time has recently reached the ultimate femtosecond resolution with the direct observation of chemical reactions as they proceed along the reaction path via transition states from reactants to products. This spectacular achievement was made possible by the development of femtosecond lasers, that is, laser pulses with a duration as short as a few femtoseconds. In a typical experiment two laser pulses are used, a pump pulse and a probe... 

Vos, M. H., Borisov, V. B., Liebl, U., Martin, J-L., Konstantinov, A. (2000) Femtosecond resolution of ligand-heme interaction in the high-affinity quinol oxidase bd a di-heme active site Proc. Natl. Acad. Sci. USA 97, 1554-1559. 

The current detailed understanding of photo-induced electron transfer processes has been advanced dramatically by the development of modern spectroscopic methods. For example, the application of time-resolved optical spectroscopy has developed from modest beginnings (flash-phyotolysis with millisecond resolution) [108,109] to the current state of the art, where laser spectroscopy with nanosecond resolution [110-113] must be considered routine, and where picosecond [114-116] or even femtosecond resolution [117] is no longer uncommon. Other spectroscopic techniques that have been applied to the study of electron transfer processes include time-resolved Raman spectroscopy [118], (time resolved) electron spin... 

Lamprecht, B., Krenn, J.R.. Leitner. A.. Aussenegg, F.R. Resonant and off-resonant light-driven pla.smon.s in metal nanoparticles studied by femtosecond-resolution third-harmonic generation. Phys. Rev. Lett. 83, 4421-4424 (1999)... 

Tire examination of molecnlar motions is facilitated by the advancing technqnies of physical stractural measurement. Sub-femtosecond resolution was achieved over a wide range of x-ray wavelengths, enabhng experimental attosecond investigations. 

One final example of ultrafast kinetics performed at radiolysis facilities is the study of excited states of radical ions. An accelerator pulse can be used to generate radical species, which can then be excited by a pump laser beam and probed with femtosecond resolution by another laser pulse with variable optical delay. This application does not depend on precise correlation of the electron and laser pulses and can be done at almost all radiolysis facilities. The availability of femtosecond lasers in photocathode facilities places all the necessary components to hand. Effective pump-probe measurements will require significant concentrations of radical ions. This can be accomplished by frequency-quadrupling a 5-9 nanosecond Nd YAG pulse to irradiate the photocathode, thereby creating a macropulse containing several tens of nanocoulombs which will produce a high concentration of radicals for the pump-probe experiment. 

A more complex apparatus is required for pico- and femtosecond studies, although the principle remains the same. With femtosecond resolution, it is possible to study the direct dissociation on a repulsive surface. An example is that of ICN — I -I-CN. The time profiles for the production of CN with the use of 100 fsec-wide pulses is shown in Figure 5.20. Because the CN group in the transition state region absorbs to the red of free CN, it is possible to monitor the time profile of the CN unit in the transition state and the appearance of free CN (Knee and Zewail, 1988). 

Figure 5 Applications of the femtosecond resolution in chemistry and biology, covering the different phases of matter and the new direction for the control of chemical dynamics [See, e.g., ref. 8,9].

Recent studies of the dynamics of electron-transfer reaction between Et and Z conducted with femtosecond resolution [15] provided further evidence that rates of DNA-mediated electron transfers are not greatly attenuated by distance. Biphasic kinetics were detected with time constants of 5 ps and 75 ps. Only the absolute amplitudes of the electron-transfer rates measured in this high-resolution study changed as a function of distance, supporting the idea that the distance dependencies of some DNA-mediated processes include contributions from events (e.g., base dynamics) occurring on a slower timescale. 

S, K. Pal, J. Peon, A.H. Zewail Biological water at the protein surface dynamical solvation probed directly with femtosecond resolution. Proc. Natl. Acad, Sci, 99, 1763 (2002)... 

---