Hollow-Core Waveguides for Spectroscopy in the Extreme Ultraviolet

Optical waveguides, such as optical fibers, are essential for numerous applications, particularly in optical communications and laser resonators. However, waveguides for extreme ultraviolet (XUV) wavelengths remain largely unexplored due to the absence of materials capable of efficiently transmitting light with wavelengths below 120 nm. In this regime, only vacuum can serve as the “core material” of the waveguide, paired with a suitable cladding material to enable high transmission [1], [2]. Previously, we demonstrated a hollow-core waveguide capable of transmitting vacuum ultraviolet light at around 124 nm [3]. The waveguide is fabricated by mechanically machining a NiP-plated substrate using an ultra-high-precision five-axis machining center developed by Canon Inc. [4]. The triangular cores are then sealed with another NiP-plated substrate to complete the waveguide (Fig. 1(a)), with a gold coating applied to the substrate as the cladding material.