  This paper proposes a novel calibration-free wavelength modulated
spectroscopy (WMS) spectral fitting technique based on the firefly algorithm.
The technique by simulating the information interaction behavior between
fireflies to achieve the retrieval of gas concentration and laser parameters.
Contrasted with the spectral fitting technique based on the classical
Levenberg-Marquardt (LM) algorithm, the retrieval of gas concentrations by this
technique is weakly dependent on the pre-characterization of the laser
parameters. We select the P(13) absorption line of C2H2 at 1532.82 nm as the
target spectra and compare the performance of two optimization method (LM and
firefly) on gas concentration and laser parameters retrieval by simulation. The
simulation results show that the spectral fitting technique based on the
firefly algorithm performs better in terms of convergence speed and fitting
accuracy, especially in the multi-parameter model without exact
characterization.
