Title: Generation of optical frequency combs via four-wave mixing processes for low- and medium-resolution astronomy,
Abstract: We investigate the generation of optical frequency combs through a cascade of
four-wave mixing processes in nonlinear fibres with optimised parameters. The
initial optical field consists of two continuous-wave lasers with frequency
separation larger than 40 GHz (312.7 pm at 1531 nm). It propagates through
three nonlinear fibres. The first fibre serves to pulse shape the initial
sinusoidal-square pulse, while a strong pulse compression down to sub-100 fs
takes place in the second fibre which is an amplifying erbium-doped fibre. The
last stage is a low-dispersion highly nonlinear fibre where the frequency comb
bandwidth is increased and the line intensity is equalised. We model this
system using the generalised nonlinear Schrödinger equation and investigate
it in terms of fibre lengths, fibre dispersion, laser frequency separation and
input powers with the aim to minimise the frequency comb noise. With the
support of the numerical results, a frequency comb is experimentally generated,
first in the near infra-red and then it is frequency-doubled into the visible
spectral range. Using a MUSE-type spectrograph, we evaluate the comb
performance for astronomical wavelength calibration in terms of equidistancy of
the comb lines and their stability.