A tuneable frequency comb via dual-beam laser-solid harmonic generation

TL;DR

This paper introduces a method to generate tunable harmonic frequency combs using dual-beam laser-solid interactions, with control achieved through observation angle and input laser frequency, offering adjustable spectral spacing.

Contribution

The study demonstrates a novel approach to produce controllable harmonic frequency combs by employing two incident laser beams at small angles on a solid target, expanding the capabilities of harmonic generation.

Findings

Harmonic spectra can be tuned via observation angle and laser frequency.

Different spectra are observed for s- and p-polarized harmonics.

Using wider laser spots reduces radiation divergence.

Abstract

A high-power laser pulse at normal incidence onto a plane solid target will generate odd harmonics of its frequency. However, the spacing of the harmonic lines in this configuration is fixed. Here, we study harmonic generation using two laser beams incident on a plane target at small, opposite angles to the target normal, via particle-in-cell simulations. When looking at the harmonic radiation in a specific direction via a narrow slit or pinhole, we select an angle-dependent subset of the harmonic spectrum. This way, we obtain a harmonic frequency comb that we control via the observation angle and the input laser frequency. The spectra for s- and p-polarised harmonics are studied separately, as they offer different frequency combs. The divergence of the harmonic radiation will be reduced by using wider laser spots, thus increasing the efficacy of the scheme. We will discuss extensions to this scheme, such as using beams with unequal frequencies, a slight tilt of the target, or employing more than two beams.