Midinfrared femtosecond laser pulse filamentation in hollow waveguides: a comparison of simulation methods

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 midinfrared wavelength region. As the wavelength of light λ=2π/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 an improved 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 alternate method offers a physically more accurate model to describe phenomena (e.g., extreme pulse-selfcompression) in waveguides with smaller values of kR.