Abstract

Expressions for the in-coupling of white noise and etalons into fitted signal strengths are derived. These show that the amount of noise picked up is affected by the scanning range. A methodology for finding the optimum scanning range from a single set of measurements has been developed. This was used to estimate the optimum conditions of a noise-immune, cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) setup. The methodology was validated by measurements. This resulted in a spectral noise equivalent absorption per unit length of $2.6\times {10}^{-13}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$ and a minimum Allan deviation of $9\times {10}^{-14}{\mathrm{cm}}^{-1}$ at 30 s, which are, to our knowledge, the lowest reported for Doppler-broadened NICE-OHMS.

© 2015 Optical Society of America

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