Energy and spectral enhancement of femtosecond supercontinuum in a noble gas using a weak seed

Abstract

We experimentally demonstrate that the use of a weak seed pulse of energy less than 0.4% of the pump results in a spectral energy enhancement that spans over 2 octaves and a total energy enhancement of more than 3 times for supercontinua generated by millijoule level femtosecond pulses in Krypton gas. Strong four-wave mixing of the pump-seed pulse interacting in the gas is observed. The spectral irradiance generated from the seeding process is sufficiently high to use white-light continuum as an alternative to conventional tunable sources of radiation for applications such as nonlinear optical spectroscopy.

Numerical investigation of enhanced femtosecond supercontinuum via a weak seed in noble gases

“…Second, for the 600 nm case there are oscillations in the enhanced spectrum in the presence of the seed for wavelengths shorter than the gap around the seed, and a peak appearing for wavelengths larger than the pump gap. The simulations therefore capture two key qualitative features of the Krypton experiment [11]. …”

“…a) The red line shows the experimental results from Ref. [11] for the enhancement as a function of seed wavelength with a peak enhancement of around 3 for a seed wavelength of around 650 nm. The blue line shows the corresponding result from the simulations, and shows a peak enhancement of around 5.4 for a seed wavelength of around 650 nm.…”

“…The authors of Ref. [11] stressed the critical role played by four-wavemixing (FWM) and we shall elucidate on this here. Earlier simulations of the above experiment by B. Shim, S. E. Schrauth, and Alex Gaeta of Cornell University, also alluded to the role of FWM in the SC generation process.…”

“…This was measured in the experiment as a function of the seed wavelength and is tabulated in the last column of Table 1 of Ref. [11] for a seed energy of 1 μJ. This enhancement is plotted versus seed wavelength in Fig.…”

“…5 of Ref. [11], for which the corresponding data set is reproduced in the inset. It, too, shows output energy versus seed energy, but with an important difference: In Fig.…”