Highly accurate key parameters extraction algorithm for Brillouin scattering spectrum using Voigt profile

The Brillouin scattering spectrum follows Voigt profile. The existing key parameters extraction algorithm for Brillouin scattering spectrum is easy to introduce errors. To ensure high accuracy in the extracted key parameters, the temperature and strain measurement, a key parameters extraction algorithm for Brillouin scattering spectrum using Voigt profile was proposed. The Voigt profile was calculated using the Gauss-Hermite quadrature, the objective function was determined based on the least-squares method and Voigt profile. Besides the initial guesses obtainment method of key parameters was presented. The objective function was optimized using the Levenberg-Marquardt algorithm. Once the objective function was minimized, the key parameters were obtained. Additionally, another algorithm was implemented, in which the initial guesses were set to some random values within a certain range, then the Levenberg-Marquardt algorithm was used to optimize the objective function. A large number of Brillouin scattering spectra with different values of signal-to-noise ratio were numerically generated and measured. The results calculated by the two algorithms reveal that the probability of convergence of the random algorithm fall within a range of 80% to 90%. The proposed algorithm always converges in all cases. The errors by the proposed algorithm are only 1/1011-1/7 of that by the random algorithm. The computation time by the proposed algorithm is only 1/8-1/3 of that by the random algorithm.