A Hilbert transform-based TDLAS second harmonic demodulation method, without reference signal.
The second harmonic in the field of wavelength modulation spectroscopy is of critical importance in the detection of gas in biomedical science, such as exhaled breath carbon dioxide.
Conventionally, lock-in amplifier is used to demodulate the second harmonic, and it requires reference signal, which is very inconvenient.
We presents a method to demodulate the second harmonic without reference signal. As no reference signal is required, the proposed method benefits second harmonic demodulation with convenient operation and efficiency.