Efficient generation of high-order harmonics in gases

TL;DR

This paper reviews the physics of high-order harmonic generation in gases, analyzing how medium parameters affect efficiency, and provides guidelines for optimizing gas target design for high-flux XUV sources.

Contribution

It offers a comprehensive analysis of macroscopic factors influencing HHG efficiency and introduces a hyperbolic relation guiding optimal medium parameters.

Findings

Efficient HHG can occur over a wide range of pressures and lengths following a hyperbolic relation.

Medium length and pressure critically influence the spatial and temporal properties of the generated radiation.

The study provides practical design guidance for high-flux XUV source development.

Abstract

High-order harmonic generation (HHG) in gases leads to short-pulse extreme ultraviolet (XUV) radiation useful in a number of applications, for example, attosecond science and nanoscale imaging. However, this process depends on many parameters and there is still no consensus on how to choose the target geometry to optimize the source efficiency. Here, we review the physics of HHG with emphasis on the macroscopic aspects of the nonlinear interaction. We analyze the influence of medium length, pressure, position of the medium and intensity of the driving laser on the HHG conversion efficiency (CE), using both numerical modelling and analytical expressions. We find that efficient high-order harmonic generation can be realized over a large range of pressures and medium lengths, if these follow a certain hyperbolic equation. The spatial and temporal properties of the generated radiation are, however, strongly dependent on the choice of pressure and medium length. Our results explain the large versatility in gas target design for efficient HHG and provide design guidance for future high-flux XUV sources.