Cavityenhanced

Cavity-enhanced refers to techniques in optics and spectroscopy that use an optical cavity to increase the interaction between light and a sample, thereby boosting sensitivity and signal strength. An optical cavity, such as a Fabry-Pérot resonator or a high‑finesse ring resonator, causes light to make many passes through the sample, effectively increasing the optical path length and the probability of interaction.

Two common families of cavity-enhanced methods are CEAS and CRDS. Cavity-enhanced absorption spectroscopy (CEAS) measures the transmitted light through a cavity with highly reflective mirrors; the sample’s absorption reduces this transmission, allowing quantification of absorber concentration. Cavity ring-down spectroscopy (CRDS) monitors the exponential decay of light inside the cavity after the light source is switched off. The decay rate is dictated by total losses, including sample absorption, providing highly sensitive measurements of trace species.

Other related approaches include cavity-enhanced Raman spectroscopy, which boosts weak Raman signals via the cavity, and cavity-enhanced photoacoustic spectroscopy, where the cavity enhances pressure waves generated by absorbed light. Key components across these methods are high-reflectivity mirrors, a stable light source, and appropriate detection and mode-matching optics. The primary advantages are increased sensitivity and, in some schemes, reduced sample volume or measurement time. Limitations include the need for precise alignment, control of cavity losses, and spectral coverage constraints due to mirror design and cavity linewidth.

Applications span trace gas detection, environmental monitoring, industrial process control, and fundamental spectroscopy, where improved detection limits and rapid analysis are valuable.