Optical frequency conversion in gas-filled hollow-core fibres

Abstract

Though the laser has now existed for over 60 years, there is still desire to develop new laser sources at the extremes of the optical spectrum. This has driven development of both mid-infrared (MIR) and ultraviolet (UV) sources. MIR and UV sources have many applications including molecular science, bio-science, and other industrial applications. These applications often have bespoke power, temporal, and wavelength requirements. The rapid development of hollow-core fibres (HCF) has enabled the use of gases as a medium for frequency conversion through nonlinear processes. Gas-filled fibres are uniquely suited to develop customized laser sources as there are many optical nonlin- earities that can be exploited in gases and prudent choice of gas species and fibre archi- tecture can enable frequency conversion to the extremes of the optical spectrum. In this thesis we present two lines of inquiry: frequency up-conversion to the deep ultraviolet (DUV) and frequency down-conversion to the MIR. These two lines of inquiry include both experimental and numerical efforts. Based on recent developments in the gen- eration of ultraviolet dispersive waves we numerically investigated the viability of a DUV source suitable to be a pump source for time-resolved photoelectron spectroscopy through adaptation of the generalized nonlinear Schrodinger equation for argon-filled HCF. With a validated code we demonstrated that output requirements can be met and developed an ultraviolet laser source based on an argon filled tubular fibre pumped with a femtosecond pulse duration laser centered at 800 nm. Ultimately achieving 95 nJ of ultraviolet light. We also developed a MIR source. We experimentally verify the vi- ability of MIR generation through a Raman cascade to the second Stokes wavelength of 2580 nm from a 1 μm source in two test fibres pressurized with methane gas while observing Raman comb generation. We then designed a custom fibre to support the transition to the second Stokes wavelength while suppressing the unwanted comb ef- fects. We optimized the output of the second Stokes signal by experimentally varying parameters to maximize the average power of the second Stokes signal. Ultimately we achieved nearly 3 W of average output power, besting the nearest comparable result by a factor of ten. Finally we modelled and simulated the methane-based source by again adapting the GNLSE to methane-filled fibres. We modelled the methane Raman response using a single-damped oscillator model; additionally we modelled both the Raman response and the other terms as a function of the gas pressure gradient which forms in the experiment.

More information

Identifiers

ORCID for Ann Marie Lanari: orcid.org/0009-0007-5525-9764

ORCID for David Richardson: orcid.org/0000-0002-7751-1058

ORCID for Francesco Poletti: orcid.org/0000-0002-1000-3083

ORCID for Hans Christian Mulvad: orcid.org/0000-0003-2552-0742

Catalogue record

Export record