Correction of resonator-induced distortions in light-induced thermoelastic spectroscopy: Second harmonic sideband perspective

Light-induced thermoelastic spectroscopy (LITES) faces long-term instability caused by resonance parameter drift, phase fluctuations, and background thermal response. This study leverages the second harmonic sideband, containing fingerprint features of resonance parameters, to overcome the limitations of conventional wavelength modulation that focuses only on the central harmonic frequency. By quantifying the distortion mechanism of the resonator on the sideband, we achieve inversion of resonance parameters and use this to perform frequency domain compensation on the photothermal signal, effectively eliminating resonator-induced distortion. Experimental results highlight the method’s ability to resist triple interference. In the surface oxidation experiment, resonance parameter inversion achieves remarkable precision, with a resonance frequency error of 0.0012 % and a quality factor error of 0.59 %. The error in C₂H₂ concentration detection significantly decreased from > 60 % to < 10 % (for concentrations ≥300 μL/L). Under phase fluctuations spanning -90° to 90°, the relative standard deviation (RSD) of the signal value decreases from 25.3 % to 2.5 %. In addition, when humidity varies from 20 % to 70 % causing resonance parameter drift, the method reduces signal fluctuation from 44 % to <5 %. This approach offers a pathway for achieving robust LITES operation in complex environments.