Phase-shift feedback cavity ring-down spectroscopy

Abstract

Phase-shift cavity-enhanced techniques have been used to measure optical losses with relatively simple electronics. Instead of measuring the phase shift, in this work the intensity modulation frequency is varied using feedback to keep the phase shift locked to a target value. The modulation frequency then becomes a signal from which cavity losses can be estimated. The technique is applied with a super luminescent diode to measure losses resulting from the addition of acetylene to a cavity containing nitrogen at ambient temperature and pressure. The technique, phase-shift feedback cavity ring down, is compared to phase-shift cavity ring-down spectroscopy.

Phase shift-cavity ring down spectroscopy in linear and active fiber cavities for sensing applications at 1550 nm

“…Numerically, it is also evident from Fig. (5) inset. In the plot, it is clear that the absorption loss is always lower when we also include glucose absorption loss as compared to water with only refractive index changes.…”

“…We then plot each curve slope against the tapered fiber's corresponding radius, as shown in Fig. (5). The blue plot considers only water absorption loss, i.e., an ideal solution that has the same absorption coefficient as water but induces refractive index changes equivalent to glucose solutions.…”

“…The change in the ring down time as a function of losses in a sample filled cavity can then be utilized for various sensing applications. For example, PS-CRDS has been utilized in numerous sensing applications for detecting gases and particles, including nitrogen dioxide [2], oxygen [3], ethene [4], acetylene [5], peroxy, organic nitrates [6], and soot particles ejecting from V 2527 aircraft engine [7]. All of these applications utilize free space cavities for detection purposes.…”