# Boosting quantum vacuum signatures by coherent harmonic focusing

## TL;DR

This paper demonstrates that coherent harmonic focusing significantly enhances the optical signatures of quantum vacuum nonlinearity, potentially enabling their first experimental detection by increasing measurable signal photons.

## Contribution

It introduces a novel use of coherent harmonic focusing to boost quantum vacuum signals, highlighting inelastic scattering as a promising detectable signature.

## Key findings

- Signal photons from inelastic scattering are promising for detection.
- Coherent harmonic focusing increases measurable signal photons.
- Quasi-elastic signals remain background dominated.

## Abstract

We show that coherent harmonic focusing provides an efficient mechanism to boost all-optical signatures of quantum vacuum nonlinearity in the collision of high-intensity laser fields, thereby offering a promising route to their first experimental detection. Assuming two laser pulses of given parameters at our disposal, we demonstrate a substantial increase of the number of signal photons measurable in experiments where one of the pulses undergoes coherent harmonic focusing before it collides with the fundamental-frequency pulse. Imposing a quantitative criterion to discern the signal photons from the background of the driving laser photons and accounting for the finite purity of polarization filtering, we find that signal photons arising from inelastic scattering processes constitute a promising signature. By contrast, quasi-elastic contributions which are conventionally assumed to form the most prospective signal remain background dominated. Our findings may result in a paradigm shift concerning which photonic signatures of quantum vacuum nonlinearity are accessible in experiment.