Mid-infrared femtosecond laser pulse filamentation in hollow waveguides: a comparison of simulation methods

TL;DR

This paper compares two computational methods for simulating mid-infrared femtosecond laser pulse filamentation in hollow waveguides, highlighting the advantages of a real-space approach over the traditional mode expansion technique.

Contribution

It introduces and validates a real-space simulation method that more accurately captures energy loss in waveguides compared to the standard mode expansion approach.

Findings

The real-space method better models energy loss in waveguides.

Mode expansion overestimates losses in nonlinear pulse reshaping.

The new method requires modest additional computational effort.

Abstract

This work compares computational methods for laser pulse propagation in hollow waveguides filled with rare gases at high pressures, with applications in extreme nonlinear optics in the mid-infrared wavelength region. As the wavelength of light \lambda=2\pi/k increases with respect to the transverse size R of a leaky waveguide, the loss of light out of the waveguide upon propagation, in general, increases. The now standard numerical approach for studying such structures is based on expansion of the propagating field into approximate leaky waveguide modes. We compare this approach to a new method that resolves the electric field in real space and correctly captures the energy loss through the waveguide wall. The comparison reveals that the expansion-based approach overestimates losses that occur in nonlinearly reshaped pulsed waveforms. For a modest increase in computational effort, the new method offers a physically more accurate model to describe phenomena (e.g., extreme pulse-selfcompression) in waveguides with smaller values of kR.