Fig. 1. (a) Transmission spectrum of the AR-HCF. (b) Scanning electron micrograph of the AR-HCF cross section. Spectra measured at the output of a 17-cm-long AR-HCF filled with 14 bar argon and pumped by 800 nm, 37 fs pulses when the single-pulse energies are (c) 1.4 μJ, (d) 1.6 μJ, and (e) 2.5 μJ, corresponding to soliton numbers N of 4.5, 5, and 6.2, respectively. The resonant bands of the AR-HCF are shown in gray shades. Red and black dashed lines mark the resonance- and capillary-model-induced phase-matching wavelengths, respectively. The generated UV spectra in the 870–1140 THz region of (c)–(e) are presented in a linear scale in (f)–(h).

Fig. 2. Soliton-dispersive wave phase-matching diagrams for gas-filled AR-HCFs with N=4.5 and cladding wall thicknesses of (a) t=470nm and (b) t=115nm. The red dots indicate the phase-matching points for UV emission. Simulated output spectra at 1.2 times the soliton fission length for AR-HCFs with wall thicknesses of (c) t=470nm and (d) t=115nm, when N=4.5, 5.5, and 6.5 (from top to bottom). The gray shades represent the resonant bands, and the red shades represent the target spectral range of the UV phase matching.

Fig. 3. (a) Bandwidth of the first resonant band versus the cladding-wall thickness of the AR-HCF with three absolute thickness variations, 20 nm, 40 nm, and 60 nm. (b) Schematic diagram of the HF etching setup for the AR-HCF.

Fig. 4. (a) Measured transmission spectra of the AR-HCFs (Fibers A–D). Gray shaded areas indicate the position of the first resonant band in each case. Scanning electron micrographs of the AR-HCF cross-sections (left) and the enlarged views of their cladding tubes (right) for (b) Fiber A, (c) Fiber B, (d) Fiber C, and (e) Fiber D. (f) Boxplots of the measured wall thickness of seven cladding tubes at different axial positions along Fibers A (left) and D (right). Red horizontal lines indicate the medians, boxes represent the interquartile ranges, and whiskers denote the full range excluding outliers, which are marked with red crosses.

Fig. 5. Experimentally measured output spectra of an N=6 pump pulse launched into argon-filled (a) Fiber B, (b) Fiber C, and (c) Fiber D. The gray shades indicate the first resonant band. The inset in (c) shows the spatial energy distribution of the UV portion (850–1200 THz) of the collected spectra, characterized using the knife-edge method. The profiles exhibit excellent agreement with Gaussian fits (solid lines).

Fig. 6. Experimentally measured (blue line) and simulated (red shaded area) output spectra when the system is pumped by the chirp-compensated pulse of 27 fs duration at its full-width at half-maximum. The inset shows temporal intensity (blue line) and chirp (red line) profiles of the compressed pump pulse obtained using the second-harmonic generation frequency-resolved optical gating technique.