Light intensity correction for light-induced thermoelastic spectroscopy based on nonlinear response of light intensity
This study presents a method for correcting light intensity in light-induced thermoelastic spec-troscopy(LITES)using a nonlinear light intensity response,enabling precise light intensity corrections.The DFB laser,set to a wavelength modulation mode at a frequency of 16369.75 Hz,benefits from en-hanced nonlinear light intensity due to a fiber amplifier.The laser beam traverses a multi-pass cell before fo-cusing on the quartz tuning fork(QTF)base,generating a thermoelastic signal.A lock-in amplifier demod-ulates the harmonic signal,and polynomial fitting of the harmonic signal's baseline extracts harmonics relat-ed to both concentration and light intensity.Experimental data reveal a strong linear correlation(coeffi-cient>0.998)between the baseline amplitude of the harmonic signal and light intensity as it varies from 22.03 mW to 3.16 mW,with normalized harmonic signal amplitude variation under 0.37%.In methane detection,the system demonstrates a robust linear response across a broad concentration range,with harmonic signal noise ratios indicating a detection threshold as low as 0.22×10-6.This research offers a novel approach for LITES light intensity correction,significantly enhancing system stability for pro-longed measurements.
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维普
