Evaluation of nonlinear absorptivity in internal modification of bulk glass by ultrashort laser pulses

Abstract

Thermal conduction model is presented, by which nonlinear absorptivity of ultrashort laser pulses in internal modification of bulk glass is simulated. The simulated nonlinear absorptivity agrees with experimental values with maximum uncertainty of  3% in a wide range of laser parameters at 10ps pulse duration in borosilicate glass. The nonlinear absorptivity increases with increasing energy and repetition rate of the laser pulse, reaching as high as 90%. The increase in the average absorbed laser power is accompanied by the extension of the laser-absorption region toward the laser source. Transient thermal conduction model for threedimensional heat source shows that laser energy is absorbed by avalanche ionization seeded by thermally excited free-electrons at locations apart from the focus at pulse repetition rates higher than 100kHz.

Strong nonlinear growth of energy coupling during laser irradiation of transparent dielectrics and its significance for laser induced damage

“…An experimental demonstration of reduced damage threshold in fused silica with temperature was found in [14]. More recently, observation of induced absorption in glasses due to ultrashort laser pulse exposure has also been reported [20]. Additionally, recent density-functional theory calculations [21] have shown that silica absorption spectra are expected to exhibit exponential tails near the band edge at elevated tempertatures.…”

Influencing the Crystallization of Glass-Ceramics by Ultrashort Pulsed Laser Irradiation after Nucleation

“…The transmitted pulse energy Q t on the backside was measured with the power meter ( Figure 1) and compared to the pulse energy Q 0 with no sample in between. The nonlinear absorption A exp was calculated with [12] ( )…”

Microscale heat transfer in fusion welding of glass by ultra-short pulse laser using dual phase lag effects

“…The laser parameters like peak power and pulse repetition rate of the ultra-short pulse laser is significant to control the width and depth of heating as well as the changes of mode i.e. laser ablation to laser welding or vice versa [7].…”

“…In fusion welding of transparent material, the laser energy is absorbed by nonlinear process with multiphoton ionization followed by avalanche ionization and the absorbed laser energy in the free electrons is transferred to the lattice to provide the temperature field in bulk glass [2,7]. Internal modification at high pulse repetition rates is due to heat accumulation effect.…”