Enhancement of vacuum-ultraviolet dispersive-wave emission using gas-filled tapered hollow-core fibers

TL;DR

This paper introduces a gas-filled tapered hollow-core fiber that enhances vacuum-ultraviolet dispersive-wave emission, providing a scalable, high-efficiency source crucial for nuclear clock and spectroscopy applications.

Contribution

The study demonstrates a novel tapered fiber design that overcomes core size trade-offs, significantly improving VUV photon flux at specific wavelengths.

Findings

Achieved twofold efficiency increase at 148.38 nm

Demonstrated tunable VUV source from 135 to 240 nm

Provided a scalable method for high-flux VUV generation

Abstract

The recent breakthroughs in laser-driving 229Th nuclear transition have created an urgent demand for coherent vacuum-ultraviolet (VUV) sources delivering high spectral brightness at the critical 148.38 nm isomer energy. However, generating sufficient photon flux to overcome the low nuclear excitation probability remains a challenge for compact setups. While resonant dispersive wave emission in gas-filled hollow-core fibers offers a promising route, standard capillaries face a fundamental trade-off: maximizing input coupling requires large core diameters, whereas efficient nonlinear VUV conversion demands the high intensities using small cores. Here, we resolve this conflict using a gas-filled tapered capillary fiber. This architecture utilizes a longitudinally decreasing core diameter to combine a large input aperture with adiabatic field concentration, thereby continuously enhancing the nonlinear interaction. Experimentally, we demonstrate a widely tunable source (135-240 nm) that achieves a twofold efficiency enhancement specifically at the 148.38 nm wavelength compared to uniform geometries. By providing a scalable route to high-flux VUV generation, this work establishes a critical tabletop tool for advancing solid-state nuclear clocks and time-resolved spectroscopy.