Low-Threshold Green-Pumped Ultraviolet Resonant Dispersive-Wave Emission in Small-Core Anti-Resonant Hollow-Fibre

Resonant dispersive-wave (RDW) emission from solitons in gas-filled hollow-core fibres is an established technique for generating tunable ultraviolet (UV) pulses [1], [2]. During soliton self-compression of the pump pulse along the fibre, its spectrum broadens until it overlaps with phase-matched wavelengths in the normal dispersion region, allowing an efficient transfer of energy to a linearly propagating RDW. In the case of hollow-core fibres, the RDW phase-matching wavelengths can be tuned simply by changing the pressure of the filling gas. UV RDW emission has been shown to be a useful tool for multiple applications, such as spectroscopy and pump-probe experiments [3], [4]. UV RDW emission is most commonly achieved using gas-filled hollow-core fibres with a core diameter ranging from
$\sim 25\ \mu \mathrm{m}$
up to
$\sim 450\ \mu \mathrm{m}$
[1], [5]. Even the lower end of this range usually requires the pump energy to be at the
$\mu \mathrm{J}$
level, requiring amplified laser systems. Recently, the use of a much smaller core size enabled the use of less than 150 nJ pump energy from a Ti:Sapphire laser to achieve UV RDW emission [6].