Circularly Polarized DUV Pulses via Dispersive Wave Emission in Hollow Capillary Fibers

Circularly polarized ultra-short laser pulses in the deep ultraviolet region (DUV, 200-400 nm) are commonly obtained via a two-step process requiring frequency up-conversion in nonlinear crystals followed by polarization conversion using quarter-wave plates. Due to strong dispersion in bulk media, this method suffers from limitations in phase-matching bandwidth, phase compensation and achromatic birefringence. Here, we demonstrate a direct process for the generation of ultra-short, circularly polarized DUV pulses via soliton dynamics in gasfilled stretched hollow capillary fibers [1] , driven by circularly polarized pulses centered at 800 nm. Frequency up-conversion occurs via resonant dispersive wave (RDW) emission with inherent spectral tunability (here we demonstrate 223-377 nm) through control of the gas (Ar) pressure. Our technique overcomes the limitations inherent to crystal-based approaches and allows energy up-scaling and extension to the vacuum UV (100-200 nm) and other spectral regions while permitting ultra-short duration, because the polarization conversion is performed at 800 nm, where material dispersion is low and the quality of commercial phase retarders is high.