Optical ablation by high-power short-pulse lasers

Abstract

Laser-induced damage threshold measurements were performed on homogeneous and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations t ranging from 140 fs to 1 ns. Gold coatings were found, both experimentally and theoretically, to be limited to 0.6 J͞cm 2 in the subpicosecond range for 1053-nm pulses. In dielectrics, we find qualitative differences in the morphology of damage and a departure from the diffusion-dominated t 1/2 scaling that indicate that damage results from plasma formation and ablation for t # 10 ps and from conventional heating and melting for t . 50 ps. A theoretical model based on electron production by multiphoton ionization, joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulse-width and the wavelength scaling of experimental results.

Ultrashort laser pulse ablation of copper, silicon and gelatin: effect of the pulse duration on the ablation thresholds and the incubation coefficients

“…The advantage of this technique is that the measurements can be performed at fluences well above threshold for which the detected fingerprint signals are clearly detectable by farfield microscopy [7]. The actual physical mechanisms of laser ablation depend on the type of materials and the irradiation properties such as laser wavelength [10], pulse duration [13][14][15][16][17][18][19] and repetition rate [14,20]. Change in the repetition rate affects the ablation threshold in two respects.…”

“…s [ 10 ps), where damage on the surface of a medium results from conventional heating and melting, the damage threshold scales as s 0.5 with pulse duration [21,22]. However, a deviation from this scaling has been observed for shorter pulses where damage results from plasma formation and ablation [17,22]. Although the ablation threshold in the short-pulse regime reduces with decreasing the pulse duration, this dependency is weaker than what is observed in the long-pulse regime.…”

Generation of ultrahigh intensity laser pulses

“…3 Damage thresholds for gratings made out of fused silica for 1 light are currently in the range of 2 -4 J/cm 2 for pulse widths of 1 to 10 ps, and about 0.3 J/cm 2 in the range of 10 fs. 4 Thus, for ps pulses, unfocused power in the range of TW/cm 2 are achievable, with a vacuum focus then able to bear on target power intensities in the range of 10 21 W/cm 2 . 2 However, to achieve very much higher focused power intensities requires compression to much shorter times of much higher fluence pulses.…”

Nano-processing Utilizing Plasmon on Glass Surface by Femtosecond Laser Pulse with Template of Dielectric Particle Array

“…A large number of electrons are generated by multiphoton ionization or avalanche ionization process. The characteristic time for this process is several tens of femtoseconds 12) at intense femtosecond laser irradiation, i.e. at the leading edge of the laser pulse used in our experiment.…”

“…The simple rate equation to calculate the free electron density n(t) was derived from Stuart et al 12) . This equation considers the multiphoton ionization and avalanche ionization process.…”