Abstract

Recovery of the full $2f$ wavelength modulation spectroscopy (WMS) signal in isolation from the $2f$ residual amplitude modulation (RAM) due to nonlinear intensity modulation (IM) and distortion due to linear IM is demonstrated. The $2f$ RAM is eliminated using a fiber delay line, while the linear IM-induced distortion is eliminated by a phasor decomposition approach. This generic and robust two-pronged strategy removes the need to separately measure the $2f$ RAM in high-modulation-index calibration-free $2f$ WMS. It is also important for widely tunable $2f$ WMS using nontelecom diode lasers with highly nonlinear characteristics leading to high-$2f$ RAM levels.

© 2010 Optical Society of America

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