Far-ultraviolet optical fibers for instrumentation in the sub-200 nm regime

Commercially available UV fibers suffer from high absorption and solarization in the far-UV range at λ < 200 nm. Recently, new hollow-core anti-resonant fiber optics (UV-HCFs) have been developed with demonstrated guidance for the first time deep into the far-ultraviolet. These fibers are fabricated at the University of Bath and tested in facilities at the University of Colorado (CU) Laboratory for Atmospheric and Space Physics (LASP). We present the optical characterization and possible applications of UV-HCFs for the 100 – 200 nm regime. Testing of the fibers involved measuring the throughput of several fiber designs and lengths, that were optimized for transmission at peak wavelengths of 160 nm and 185 nm. The transmission of the fibers is measured using a far-UV monochromator and deuterium light source, connected to a custom alignment apparatus contained within a nitrogen-purged enclosure. The throughput is detected and logged using a photomultiplier tube and supporting autonomous control and data collection software. Our measurements show more than 50 percent throughput for a 20 cm fiber at approximately 160 nm, and performance that matches model predictions at wavelengths as low as 122 nm. The performance of the fibers will allow for the extension of the energy range of fiber-fed spectrographs and Raman spectrometer/reflectometers. Our results show that UV-HCFs have promise for future scientific applications.