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.

400-Hz mechanical scanning optical delay line

Abstract: We have developed a simple, high-speed, nearly vibration-free, mechanically scanned, optical delay line suitable for femtosecond time-resolved signal-averaging measurements. We demonstrate a 2-ps time window autocorrelator with a display updated at 400 Hz. The delay line uses a dithering planar mirror as a time-varying linear phase ramp in the spectral plane of a modified grating-lens femtosecond pulse shaper. The time delay is linearly proportional to the angular deviation of the mirror. The high speed and low vibration are a result of the extremely small angular changes required to generate a large time delay.

Nano-Sized Hollow Bump Array Generated by Single Femtosecond Laser Pulse

Abstract: The generation of a nano-sized hollow bump array of gold thin film by uniformly spaced melting and inflation of the film induced by a single shot of four interfering fs laser beams is reported. The shape changed from a bump, to a bead on bump, to a standing bead on a hole, and finally to a hole, with the increase in fs laser fluence. The bump height, diameter, and shape as functions of laser fluence are shown. Moreover, the basic shape of the bump changed upon changing the number of interfering beams.

Anharmonic Lattice Dynamics in Germanium Measured with Ultrafast X-Ray Diffraction

Abstract: Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium.

Thermoelastic modeling of microbump and nanojet formation on nanosize gold films under femtosecond laser irradiation

Abstract: A model of elasto-plastic flow combined with the two-temperature model in a two-dimensional approximation has been developed to describe microbump and nanojet formation observed recently on nanosize gold films irradiated by femtosecond laser pulses. It has been shown that the effect of microbump and nanojet formation is conditioned by the elastic characteristics, yield stress, and other properties that are unique for gold. The numerical results are in excellent agreement with the experimental data with respect to a number of parameters, particularly the threshold fluence for nanojet formation at the tops of microbumps, which occurs nearby and above the melting threshold. The analysis of properties for a number of materials is performed and some other materials are discussed as possible candidates for nanotexturing of thin films by femtosecond laser pulses.

Origin of third-order optical nonlinearity in Au:SiO(2) composite films on femtosecond and picosecond time scales.

Abstract: Three sorts of probe laser, which have pulse durations of 200??fs, 35??ps, and 70??ps, were employed in the measurement of the third-order nonlinear optical susceptibility ?3 in Au:SiO2 composite films in a degenerate four-wave mixing scheme. We found that the composite films at their absorption peak ?550 nm had a maximum ?3, which depends strongly on the pulse width of the probe laser. The value of ?3 measured with a 70-ps laser was ?30 times larger than that measured with a 200-fs laser. The time-resolved measurements revealed that the optical nonlinearity on the femtosecond time scale is attributable mainly to contributions from the interband electric–dipole transition (especially at low concentrations) and partly to those from hot electrons rather than being dominated by hot-electron excitation in the picosecond regime.