Topic
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.
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TL;DR: A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations.
Abstract: Sequential multiple photoionization of the prototypical molecule N2 is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.
172 citations
TL;DR: In this paper, the ultrafast dynamics of gain and refractive index in an electrically pumped InAs-InGaAs quantum-dot (QD) optical amplifier are measured at room temperature using differential transmission with femtosecond time resolution.
Abstract: The ultrafast dynamics of gain and refractive index in an electrically pumped InAs-InGaAs quantum-dot (QD) optical amplifier are measured at room temperature using differential transmission with femtosecond time resolution. Both absorption and gain regions are investigated. While the absorption bleaching recovery occurs on a picosecond time scale, the gain compression recovers with /spl sim/100-fs time constant, making devices based on such dots promising for high-speed optical communications.
171 citations
TL;DR: In this article, the authors report real-time observations of ultrafast molecular vibrations and rotations using femtosecond laser pulses, where the system is prepared in the particular state(s) of interest by coherent excitation with an initial femtocond laser pulse, and the subsequent motions are probed with successive femto-cond pulses.
Abstract: Ultrafast molecular vibrations and rotations are the fundamental motions that characterize chemical bonding and determine reaction dynamics at the molecular level. The timescales for these motions are typically 10^(−10) s for vibrations and 10^(−13) s for rotations. For decades, time-integrated (frequency-resolved) spectros-copy has provided a powerful tool for probing the dynamics of motion, but the motions themselves are not 'seen' directly in real-time. With femtosecond laser techniques it is now possible to follow the motions of isolated molecular systems as they occur. The requirement is that the system is excited (for vibration) and aligned (for rotation) on a timescale shorter than the vibrational and rotational periods. Here we report real-time observations of these molecular motions. The system—in this case, molecular iodine—is prepared in the particular state(s) of interest by coherent excitation with an initial femtosecond laser pulse, and the subsequent motions are probed with successive femtosecond pulses. The probe monitors changes in the interatomic distance (vibration) or molecular orientation (rotation), so that the measured signal provides direct 'snapshots' of the molecular motions.
171 citations
Journal Article•
TL;DR: In this paper, femtosecond laser micromachining has attracted vivid attention in various industrial fields and in medicine owing to the advantages of ultrashort laser pulses compared to long-pulse treatment.
Abstract: Femtosecond laser micromachining has excited vivid attention in various industrial fields and in medicine owing to the advantages of ultrashort laser pulses compared to long-pulse treatment. These are mainly the reduction of the laser fluence needed to induce ablation and the improvement of the contour sharpness of the laser-generated structures. Recently, special attention was paid to femtosecond laser experiments on nonabsorbing inorganic dielectrics. This is due to the fact that optical damage in dielectric optical elements limits the performance of high-power laser systems. Despite the fact that a large variety of organic polymers can be machined with excimer lasers successfully, the involvement of thermal processes can lead to an unsatisfactory quality of the structures. Ultrashort, fs-laser pulses might be an alternative for the treatment of polymers. Therefore, femtosecond laser machining investigations of dielectrics and polymers are reviewed in this paper. Similarities and differences of the ablation behavior of both material classes are discussed. The influence of the bandgap on the ablation threshold in dependence on the pulse duration, the enhancement of the machining precision with a shortening of the pulse duration, incubation phenomena, and morphological features appearing on the surface after femtosecond laser treatment are mentioned. Possible applications, e.g., in medicine and biosensors, are described.
171 citations
TL;DR: In this paper, the design and characterization of a femtosecond high-intensity laser system emitting a near-diffraction-limited beam was presented, which was dimensioned in order to reach intensities in excess of 1020 W/cm2 at a high repetition rate for ultrahigh-field physics experiments.
Abstract: We present the design and characterization of a femtosecond high-intensity laser system emitting a near-diffraction-limited beam. This system was dimensioned in order to reach intensities in excess of 1020 W/cm2 at a high repetition rate for ultrahigh-field physics experiments. We describe the improvements that were added to a conventional chirp pulse amplification configuration in order to decrease the deleterious effects of gain narrowing, gain shifting, thermal focusing in the amplifier stages, and spatial degradation due to multipass amplification processes.
171 citations