Characteristics of light reflected from a dense ionization wave with a tunable velocity

TL;DR

This paper investigates how a dense ionization wave generated by crossing femtosecond laser pulses can efficiently convert light into tunable coherent x-rays, with spectra influenced by pulse parameters and wave velocity.

Contribution

It demonstrates a method to produce tunable coherent x-rays using an optically-dense ionization wave with controllable velocity, enabling wavelength tuning and spectral manipulation.

Findings

Ionization wave velocity can be tuned by adjusting the crossing angle of laser pulses.

X-ray spectra vary from monochromatic to harmonic-like depending on pulse duration and intensity.

Spectral asymmetry occurs when wave velocity is below or above the speed of light.

Abstract

An optically-dense ionization wave (IW) produced by two femtosecond laser pulses focused cylindrically and crossing each other is shown to be an efficient coherent x-ray converter. The resulting velocity of a quasi-plane IW in the vicinity of pulse intersection increases with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing an easy tuning the wavelength of x-rays. The x-ray spectra of a converted, lower frequency coherent light change from the monochromatic to a high order harmonic-like with the duration of ionizing pulses and the intensity of scattered pulses; the spectrum are not symmetrical at V<c and V>c.