Self-focusing in air with phase-stabilized few-cycle light pulses

Abstract

We investigate the nonlinear optical phenomenon of self-focusing in air with phase-stabilized few-cycle light pulses. This investigation looks at the role of the carrier-envelope phase by observing a filament in air, a nonlinear phenomenon that can be utilized for few-cycle pulse compression [Appl. Phys. B79, 673 (2004)]. We were able to measure the critical power for self-focusing in air to be 18+/-1 GW for a 6.3 fs pulse centered at 800 nm. Using this value and a basic first-order theory, we predicted that the self-focusing distance should deviate by 790 mum as the carrier-envelope phase is shifted from 0 to pi/2 rad. In contrast, the experimental results showed no deviation in the focus distance with a 3sigma upper limit of 180 mum. These counterintuitive results show the need for further study of self-focusing dynamics in the few-cycle regime.

Handling beam propagation in air for nearly 10-fs laser damage experiments

“…This value of critical power experimentally retrieved from our experiments is significantly smaller than other critical power measured in air (10 GW for τ¼42 fs, 5 GW for τ4200 fs [33] and 18 GW for τ¼6.3 fs [13]), and it is likely that our measurement performed in a rather strong converging geometry compared to others experiments may be significantly skewed by other competing nonlinear effects like air ionization [14]. A rather high critical power was expected when using ultrashort pulse (like in our experiment) because only the instantaneous electron contribution to Kerr effect could contribute in this temporal regime and not the delayed Kerr effect related to the response of the nucleus [38].…”

“…Indeed, if we assume the interaction of a 10 fs laser pulse of 10 mJ energy at the surface of a dielectrics, one should expect a laser-induced threshold for ablation in the range of 1 J/cm² [11,12]). However, it corresponds to an incident beam power close to the critical power in air ( $ 10 GW [13,14]) and an intensity in the Rayleigh range close to air ionization and intensity clamping ( $ 5 Â 10 13 -10 14 W/cm² for pulse range of 100 fs duration [15][16][17][18][19]). In those conditions, maintaining the optical properties of the incident laser beam till the sample located in the focal plane of a focusing element may be highly questionable.…”

Absolute measurement of the transient optical nonlinearity in N2, O2, N2O, and Ar

“…Previously, the pulse-width dependence of the Kerr effect had been probed only indirectly by measurements of critical power in self-focusing [12,29]. However, it was recently shown that critical power measurements can be complicated by defocusing effects from plasma generation [30].…”

Carrier-envelope phase-dependent electronic conductivity in an air filament driven by few-cycle laser pulses

“…These interpretations have not been verified experimentally [13]. In 2010, Laban et al predicted that the length of the filament generated by 6.3-fs laser pulses in air should * hteng@iphy.ac.cn † zywei@iphy.ac.cn change by 790-μm the CEP shifted π/2 rad; to the best of our knowledge, there is no clear experimental evidence to support this prediction [14]. In fact, the CEP effect during the interaction between the laser and air filament has not been fully investigated.…”