Logarithmic demodulator for laser Wavelength-Modulaton Spectroscopy

A method comprising:

• filtering an analog signal at a first filter, wherein the first filter has a central frequency of of which is a harmonic of frequency f;
• generate a first filtered analog signal from the filtered analog signal at the first band-pass filter;
• filtering the analog signal at a second filter wherein the second filter has a central frequency of f;
• generate a second filtered analog signal from the filtered analog signal at the first band-pass filter;
• convert the first filtered analog signal to a first demodulated signal by a first demodulation converter;
• applying the second filtered analog signal to a second demodulated signal by a second demodulation converter;
• and
• generate a differential signal by subtracting the first demodulated signal from the second demodulated signal by a differentiator.

A system comprising:

• a first band-pass filter, wherein the first band-pass filter is configured to receive and filter a detector signal, and wherein the first band-pass filter has a central frequency of nf which is a harmonic of frequency f;
• a second band-pass filter, wherein the second band-pass filter is configured to receive and filter the detector signal, and wherein the second band-pass filter has a central frequency of f;
• a first demodulation converter, wherein the first demodulation converter is configured to apply the filtered detector signal from the first band-pass filter;
• a second demodulation converter, wherein the second demodulation converter is configured to apply the filtered detector signal from the second band-pass filter;
• and
• a differentiator, wherein the differentor is configured to subtract the applied signal from the first demodulation converter from the applied signal from the second demodulation converter.