PROCEEDINGS ARTICLE | May 12, 2011
Proc. SPIE. 8032, Next-Generation Spectroscopic Technologies IV
KEYWORDS: Photodetectors, Mirrors, Beam splitters, Tunable lasers, Spectroscopy, Heterodyning, Signal processing, Optical resonators, Signal detection, Filtering (signal processing)
Cavity ringdown spectroscopy (CRDS) measures the decay time, of a resonant optical cavity containing a measurand, as
a function of optical frequency. The measurand is identified and quantified by the cavity decay time, which is modified
by the measurand within. As coupling light into a high-finesse optical cavity is difficult, the throughput of the cavity is
small. A recent variant, swept-cavity heterodyne CRDS, interferes backward escaping cavity light, with light reflected
from the cavity input mirror, providing better signal sensitivity due to the heterodyne advantage. The measured
interference signal is demodulated and log-amplified to produce a signal whose slope is representative of the cavity
decay time. This paper, for the first time, examines the conditions required for high-fidelity measurements of the cavity
decay time using swept-cavity heterodyne CRDS and log-amplification technique. We demonstrate that, due to the very
large bandwidth and dynamic range of the log-amplifier, for realistic measurement conditions, the log-amplifier does not
impose any significant restrictions on the measurement accuracy. We also demonstrate, however, the measurement
accuracy is limited by two factors, the detector bandwidth, and segment of acquired data used to measure the slope.
