Pulse duration

About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.

Ablation of solids by femtosecond lasers: ablation mechanism and ablation thresholds for metals and dielectrics

Abstract: The mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form. It is shown that at high intensities when the ionization of the target material is complete before the end of the pulse, the ablation mechanism is the same for both metals and dielectrics. The physics of this new ablation regime involves ion acceleration in the electrostatic field caused by charge separation created by energetic electrons escaping from the target. The formulae for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data. The calculated dependence of the ablation thresholds on the pulse duration is in agreement with the experimental data in a femtosecond range, and it is linked to the dependence for nanosecond pulses.

Short-pulse laser damage in transparent materials as a function of pulse duration

Abstract: We present a single-shot damage threshold measurement and modeling for fused silica at 800 nm as a function of pulse duration down to 20 fs. We examine the respective roles of multiphoton ionization, tunnel ionization, and impact ionization in laser damage. We find that avalanche predominates even in the case of sub-100-fs pulses.

Theory of mode locking with a slow saturable absorber

Abstract: A closed-form solution is presented for the pulses of a homogeneously broadened laser mode locked by a saturable absorber of relaxation time much longer than the pulsewidth. With suitable approximations, the pulse shape is a secant hyperbolic. The system is described in terms of the linewidth omega C of the system, the saturation energies of the saturable absorber and the laser medium, the ratio of saturable-absorber loss to resonator loss, and the ratio of cavity round-trip time and laser-medium relaxation time. The energy and width of the pulse are obtained as functions of these parameters. Graphs are presented for the operating regimes as bounded by the choice of the preceding parameters. The theoretical predictions are compared with second-harmonic-generation (SHG) autocorrelation traces of mode-locked dye-laser pulses.

Laser-induced plasma formation in water at nanosecond to femtosecond time scales: calculation of thresholds, absorption coefficients, and energy density

Abstract: The generation of plasmas in water by high-power laser pulses was investigated for pulse durations between 100 ns and 100 fs on the basis of a rate equation for the free electron density. The rate equation was numerically solved to calculate the evolution of the electron density during the laser pulse and to determine the absorption coefficient and energy density of the plasma. For nanosecond laser pulses, the generation of free electrons in distilled water is initiated by multiphoton ionization but then dominated by cascade ionization. For shorter laser pulses, multiphoton ionization gains ever more importance, and collision and recombination losses during breakdown diminish. The corresponding changes in the evolution of the free carrier density explain the reduction of the energy threshold for breakdown and of the plasma energy density observed with decreasing laser pulse duration. By solving the rate equation, we could also explain the complex pulse duration dependence of plasma transmission found in previous experiments. Good quantitative agreement was found between calculated and measured values for the breakdown threshold, plasma absorption coefficient, and plasma energy density.