Necklace-structured high harmonic generation for low-divergence, soft X-ray harmonic combs with tunable line spacing

TL;DR

This paper introduces a necklace-shaped phased array of high-harmonic emitters that produces low-divergence, tunable line spacing soft X-ray harmonic combs, advancing control over harmonic beam properties for applications in ultrafast science.

Contribution

It presents a novel transverse phased array design for HHG that enables tunable line spacing and ultra-low divergence in soft X-ray harmonic generation, expanding the design space for harmonic combs.

Findings

On-axis HHG emission exhibits extremely low divergence, decreasing with harmonic order.

The necklace-shaped array allows tuning of line spacing via orbital angular momentum conservation.

The approach enhances control over harmonic beam properties in the soft X-ray regime.

Abstract

The extreme nonlinear optical process of high-harmonic generation (HHG) makes it possible to map the properties of a laser beam onto a radiating electron wavefunction, and in turn, onto the emitted x-ray light. Bright HHG beams typically emerge from a longitudinal phased distribution of atomic-scale quantum antennae. Here, we form a transverse necklace-shaped phased array of HHG emitters, where orbital angular momentum conservation allows us to tune the line spacing and divergence properties of extreme-ultraviolet and soft X-ray high harmonic combs. The on-axis HHG emission has extremely low divergence, well below that obtained when using Gaussian driving beams, which further decreases with harmonic order. This work provides a new degree of freedom for the design of harmonic combs, particularly in the soft X-ray regime, where very limited options are available. Such harmonic beams can enable more sensitive probes of the fastest correlated charge and spin dynamics in molecules, nanoparticles and materials.