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.

Femtosecond laser processing system with process parameters, controls and feedback

Abstract: A femtosecond laser based laser processing system having a femtosecond laser, frequency conversion optics, beam manipulation optics, target motion control, processing chamber, diagnostic systems and system control modules. The femtosecond laser based laser processing system allows for the utilization of the unique heat control in micromachining, and the system has greater output beam stability, continuously variable repetition rate and unique temporal beam shaping capabilities.

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Abstract: Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pump-probe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, beta of (similar to 2-9) x 10(-8) cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130-330 fs (related to carrier-carrier scattering) followed by it slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are observed. (C) 2009 American Institute of Physics.

Time dependence of the laser-induced femtosecond lattice instability of Si and GaAs: Role of longitudinal optical distortions.

Abstract: We extend our previous analysis of the ultrafast laser-induced instability of the diamond structure of semiconductors by including longitudinal optical-phonon distortions in addition to the instability of the transverse acoustic phonons. Generally, longitudinal optical distortions enhance the instability of the transverse acoustic phonons, increasing the kinetic energy of the atoms and the final lattice temperature. These phonons make a transition to a centrosymmetric structure of GaAs with metallic properties possible. We present results for the time dependence of the instability of Si for the case where 15% of the valence electrons have been excited into the conduction band. Thus, already 100 fsec after the excitation of the plasma the atoms are displaced about 1 \AA{} from their equilibrium position and their kinetic energy has increased to approximately 0.4 eV. Collisions between the atoms then lead to a rapid melting of the crystal. These results are in good agreement with recent experiments performed on Si and GaAs.

Reversible Optical Switching of Infrared Antenna Resonances with Ultrathin Phase-Change Layers Using Femtosecond Laser Pulses

Abstract: Recently, phase-change materials (PCMs) have gained a lot of interest in the field of active metamaterials and plasmonics due to their switchable optical properties. In the infrared spectral range the huge contrast in the refractive index between an amorphous and a crystalline phase can be employed for nonvolatile tuning of nanoantenna or metasurface resonances. To make use of such concepts in devices, the reversible switching of the active material has to be realized. Here we demonstrate such reversible cycling by applying femtosecond pulses from a Ti:sapphire laser. These optical pulses trigger the phase transitions of the PCM thin film, which is covering infrared nanoantennas. Ge3Sb2Te6 is chosen as the PCM, since it offers very low losses in the infrared spectral range. The layer geometry presented is exceptionally thin (∼1/50 of the operating wavelength) and the design intentionally avoids lossy capping layers. Infrared reflectivity measurements verify the laser-induced resonance shifts of the plasmo...

Breakup and fusion of self-guided femtosecond light pulses in air.

Abstract: We report experiments showing the breakup and the merging of filaments formed by the modulational instability of femtosecond optical pulses in air. For input powers as high as 25 times the self-focusing threshold, the beams are shown to split into two spots, which coalesce into a self-guided beam. This effect occurs in an optically Kerr regime and plays an important role in the guiding process. Numerical simulations and theoretical estimates both support the comparison with the experimental data.