Ionization-Induced Self-Compression of Tightly Focused Femtosecond Laser Pulses

Abstract

As lasers become progressively higher in power, optical damage thresholds will become a limiting factor. Using the nonlinear optics of plasma may be a way to circumvent these limits. Here, we present a new self-compression mechanism for high-power, femtosecond laser pulses based on geometrical focusing and three dimensional spatiotemporal reshaping in an ionizing plasma. By propagating tightly focused, 10-mJ femtosecond laser pulses through a 100-μm gas jet, the interplay between ionization gradients, focusing, and diffraction of the light pulse leads to stable and uniform self-compression of the pulse, while maintaining a high-energy throughput and excellent refocusability. Self-compression down to 16 fs from an original 36-fs pulse is measured using second-harmonic-generation frequency-resolved optical gating. Using this mechanism, we are able to maintain a high transmission (>88%) such that the pulse peak power is doubled. Three-dimensional numerical simulations are performed to support our interpretation of the experimental observations.

Self-focusing and self-compression of intense pulses via ionization-induced spatiotemporal reshaping

“…This effect is initially demonstrated numerically in one dimensional case [14] with ionizationinduced chirp [6] and is weaker when defocusing is considered [15]. Ionization-induced compression was also demonstrated experimentally in capillaries or under tight focusing, where the required chirp is mediated by the strong spatiotemporal coupling [16,17].…”

Coherent control of plasma dynamics by feedback-optimized wavefront manipulationa)

“…In this section, we apply the wavefront shaping optimization to the pulse compression experiments. 22 With no changes to the experimental setup, we program the measurement result into the genetic algorithm, with a straightforward fitness function FOM ¼ 1=s L , where s L is the retrieved FWHM pulse duration from the commercial FROG device (Swamp Optics 8-9-thin-USB). The goal of the optimization is to decrease s L .…”

“…In Ref. 22, we have shown the pulse compression occurs as a result of complex spatial-temporal coupling induced by ionization and propagation in the mid-field region of a tightly focused laser beam. Naturally, the laser wavefront conditions are likely to play a role here.…”

“…Here we further show that optimization leads to an improved quality diffraction pattern. The feedback optimization was also used for a laser plasma experiment in which optical self-compression occurs as a result of ionization nonlinearity and spatiotemporal reshaping, 22 achieving an additional reduction in the pulse duration by applying a feedback-optimized wavefront configuration.…”

Relativistic laser pulse compression in magnetized plasmas

“…Moreover, selfcompression down to 16 fs from an original 36 fs laser pulse is realized in lab experiments in Ref. 26. And the selfcompression of intense short linearly polarized laser pulses in relativistic magnetized plasma is investigated in Ref.…”