Photon Acceleration in a Flying Focus

TL;DR

This paper introduces a flying focus technique to enhance photon acceleration, enabling extreme ultraviolet and potential x-ray generation in a compact setup by overcoming previous limitations.

Contribution

The study demonstrates, through theory and simulations, that a flying focus can significantly improve photon upshifting, paving the way for compact coherent x-ray sources.

Findings

Flying focus enables extreme ultraviolet photon upshifting over centimeters.

Analytic model predicts potential for table-top coherent x-ray sources.

Simulations confirm the effectiveness of the flying focus in photon acceleration.

Abstract

A high-intensity laser pulse propagating through a medium triggers an ionization front that can accelerate and frequency-upshift the photons of a second pulse. The maximum upshift is ultimately limited by the accelerated photons outpacing the ionization front or the ionizing pulse refracting from the plasma. Here we apply the flying focus--a moving focal point resulting from a chirped laser pulse focused by a chromatic lens--to overcome these limitations. Theory and simulations demonstrate that the ionization front produced by a flying focus can frequency-upshift an ultrashort optical pulse to the extreme ultraviolet over a centimeter of propagation. An analytic model of the upshift predicts that this scheme could be scaled to a novel table-top source of spatially coherent x-rays.