  This paper develops a spectral fitting technology based on the particle swarm
optimization (PSO) algorithm, which is applied to a calibration-free wavelength
modulation spectroscopy system to achieve concentration retrieval. As compared
with other spectral fitting technology based on the Levenberg-Marquardt (LM)
algorithm, this technology is relatively weakly dependent on the
pre-characterization of the laser parameters. The gas concentration is
calculated by fitting the simulated spectra to the measured spectra using the
PSO algorithm. We validated the simulation with the LM algorithm and PSO
algorithm for the target gas C2H2. The results showed that the convergence
speed of the spectral fitting technique based on the PSO algorithm was about 63
times faster than the LM algorithm when the fitting accuracy remained the same.
Within 5 seconds, the PSO algorithm can produce findings that are generally
consistent with the values anticipated.

Instrumentation and Detectors