Femtosecond

About: Femtosecond is a research topic. Over the lifetime, 35106 publications have been published within this topic receiving 691405 citations. The topic is also known as: 1 E-15 s & fs.

Clocking transient chemical changes by ultrafast electron diffraction

Abstract: With the advent of femtosecond (fs) time resolution in spectroscopic experiments, it is now possible to study the evolution of nuclear motions in chemical and photobiochemical reactions. In general, the reaction is clocked by an initial fs laser pulse (which establishes a zero of time) and the dynamics are probed by a second fs pulse; the detection methods include conventional and photoelectron spectroscopy and mass spectrometry. Replacing the probe laser with electron pulses offers a means for imaging ultrafast structural changes with diffraction techniques, which should permit the study of molecular systems of greater complexity (such as biomolecules). On such timescales, observation of chemical changes using electron scattering is non-trivial, because space-charge effects broaden the electron pulse width and because temporal overlap of the (clocking) photon pulse and the (probe) electron pulse must be established. Here we report the detection of transient chemical change during molecular dissociation using ultrafast electron diffraction. We are able to detect a change in the scattered electron beam with the zero of time established unambiguously and the timing of the changes clocked in situ. This ability to clock changes in scattering is essential to studies of the dynamics of molecular structures.

Femtosecond time-resolved molecular multiphoton ionization: The Na2 system.

Abstract: We report here the first experimental study of femtosecond time-resolved molecular multiphoton ionization. Femtosecond pump-probe techniques are combined with time-of-flight spectroscopy to measure transient ionization spectra of ${\mathrm{Na}}_{2}$ in a molecular-beam experiment. The wave-packet motions in different molecular potentials show that incoherent contributions from direct photoionization of a singly excited state and from excitation and autoionization of a bound doubly excited molecular state determine the observed transient ionization signal.

Measurement of Temperature-Independent Femtosecond Interfacial Electron Transfer from an Anchored Molecular Electron Donor to a Semiconductor as Acceptor

Abstract: Modified perylene chromophores were adsorbed with virtually constant reaction distance on the surface of a spongelike TiO2 electrode. Interfacial electron transfer was probed with femtosecond resolution in ultrahigh vacuum via transient absorption and fluorescence up-conversion measurements. Identical time constants were measured for the decay of the reactant and rise of the product states. The dominant fast time constant was 190 fs. It remained constant between 300 and 22 K.

Time-resolved observations of shock waves and cavitation bubbles generated by femtosecond laser pulses in corneal tissue and water

Abstract: Background and Objective Photodisruption in ocular media with high power pulsed lasers working at non-absorbing frequencies have become a well established surgical tool since the late seventies Shock waves and cavitation bubbles generated by the optical breakdown may strongly influence the surgical effect of photodisruptive lasers We have investigated the shock wave and cavitation bubble effects of femtosecond laser pulses generated during photodisruption in corneal tissue and water The results are compared to those obtained with longer laser pulses Study Design/Materials and Methods Laser pulses with 150 fs duration at ∼620 nm wavelength have been focused into corneal tissue and water to create optical breakdown Time-resolved flash photography has been used to investigate the dynamics of the generated shock waves and cavitation bubbles Results A rapid decay of the shock waves is observed in both materials with similar temporal characteristics and with a spatial range considerably smaller than that of shock waves induced by picosecond (or nanosecond) optical breakdown Cavitation bubbles are observed to develop more rapidly and to reach smaller maximum diameter than those generated by longer pulses In corneal tissue, single intrastromal cavitation bubbles generated by femtosecond pulses disappear within a few tens of seconds, notably faster than cavitation bubbles generated by picosecond pulses Conclusions The reduced shock wave and cavitation bubble effects of the femtosecond laser result in more localized tissue damage Therefore, a more confined surgical effect should be expected from a femtosecond laser than that from picosecond (or nanosecond) lasers This indicates a potential benefit from the applications of femtosecond laser technology to intraocular microsurgery © 1996 Wiley-Liss, Inc