Optical Shock-Enhanced Self-Photon Acceleration

TL;DR

This paper demonstrates a novel method for self-photon acceleration using a shaped laser pulse that creates a guiding density profile, enabling dramatic spectral broadening and optical shock formation, resulting in multi-octave spectra over very short interaction lengths.

Contribution

It introduces a new regime of photon acceleration utilizing a shaped laser pulse to form a guiding density profile, significantly enhancing spectral broadening and optical shock effects.

Findings

Achieved multi-octave spectra from 400 nm to 60 nm.

Generated near-transform limited <400 as pulses.

Realized spectral broadening over less than 100 μm of interaction length.

Abstract

Photon accelerators can spectrally broaden laser pulses with high efficiency in moving electron density gradients. When driven by a conventional laser pulse, the group velocity walk-off experienced by the accelerated photons and deterioration of the gradient from diffraction and refraction limit the extent of spectral broadening. Here we show that a laser pulse with a shaped space-time and transverse intensity profile overcomes these limitations by creating a guiding density profile at a tunable velocity. Self-photon acceleration in this profile leads to dramatic spectral broadening and intensity steepening, forming an optical shock that further enhances the rate of spectral broadening. In this new regime, multi-octave spectra extending from $400 nm - 60 nm$ wavelengths, which support near-transform limited $< 400 as$ pulses, are generated over $<100 \mu$m of interaction length.