Absorption sensitivity enhancement in methyl fluoride at 1200cm^−1 using Stark polarization rotation

Polarization rotation using a modulated electric field is demonstrated in methyl fluoride vapor as a technique to reduce source noise in diode-laser absorption spectroscopy. A comparison of this technique with amplitude modulation and Stark modulation is presented, showing that this technique decreases the effect of source noise and thus provides improved sensitivity. A discussion is presented of the magnitude of the polarization rotation for different J, K rotational transitions that occur in a symmetric top. The effect of the crossing angle of the polarization analyzer on the polarization rotation signal and the source-noise reduction is studied in order to obtain the operating conditions for maximum signal-to-noise ratio.