Abstract
A novel method for online correction of light intensity fluctuation in a
practical tunable diode laser absorption spectroscopy (TDLAS) system with wavelength
modulation is presented. The proposed method is developed according to the linear
relation between peaks at multiple frequencies of sine modulation in the power
spectral density of the demodulated second-harmonic (2f) signal and the incident
light intensity. Those peaks are demonstrated experimentally and explained as
residual power at the first-harmonic and third-harmonic frequencies after 2f
demodulation of the residual amplitude modulation signal due to the limited
integrating time constant of the lock-in-amplifier. This method can achieve
real-time correction of light intensity fluctuations with only little calculation.
It can work well in a very large range of light intensity and has great potential
applications in the wavelength modulation spectroscopy system.
© 2012 Chinese Optics Letters
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