Supercontinuum generation with picosecond ultraviolet pulses in a solid-core photonic crystal fiber

Black light supercontinuum generation is demonstrated as a result of picosecond pumping a solid-core photonic crystal fiber at 355~nm through the combined effects of intermodal four-wave mixing and cascaded Raman scattering. OCIS codes: 190.4370, 190.5650, 190.4005. The study of supercontinuum (SC) generation in photonic crystal fibers (PCF) continues to be an area of active research, motivated by many applications in bio-photonics, optical metrology, spectroscopy, and imaging. Although many previous reports on SC generation have used PCFs pumped with near infrared or visible lasers [1–5], studies of SC generation using UV laser have not yet been investigated. In this work, we report the observation of a broadband continuum spanning from 350 to 470 nm, i.e., in the black-light region of the electromagnetic spectrum, as a result of picosecond pumping a solid-core silica photonic crystal fiber at 355 nm. This was achieved despite both the strong absorption and large normal groupvelocity dispersion (GVD) of silica glass in the UV. Further investigations reveal that the continuum generation results from the interplay of intermodally phase-matched four-wave mixing and cascaded Raman scattering. In our experiment, we used a standard solid-core silica PCF similar to those usually used for SC generation when pumping at 1064 nm in the small anomalous dispersion regime [4]. It has a triangular lattice with pitch and holes diameters of 3.88 μm and 2.73 μm, respectively. Its zero-dispersion wavelength is 1044 nm. At 355 nm, our PCF exhibits a large normal GVD dominated by material dispersion (D=-1720 ps/nm/km). In addition, the PCF carries several propagation modes at 355 nm that have been numerically identified as the LP01, LP11 and LP31 modes using a finite element method.