Cavity ring down spectroscopy (CRDS) is a high-sensitivity optical absorption technique that measures how long laser light persists inside a high‑finesse optical cavity to determine trace gas concentrations. In practice, CRDS records the light decay (ring‑down) time caused by absorption from target molecules; the decay time is converted to an absolute absorption value and then to concentration. 

Technical Specifications of Tiger Optics CRDS

Cavity Ring-Down Spectroscopy: Principles, Applications, and Benefits,

Trace Moisture Analysis with CRDS

How CRDS Cavity Ring Down Spectroscopy Work

CRDS uses a pair of highly reflective mirrors to form an optical cavity. A laser (typically a continuous‑wave, wavelength‑tuned source for modern analyzers) injects light into the cavity. When the laser is gated off or decoupled from the cavity mode, the trapped light decays exponentially as it reflects between the mirrors. The presence of an absorbing species shortens that decay time; by measuring the ring‑down time precisely and comparing it to the empty‑cavity baseline, the system calculates absolute absorption and thus concentration.

• Key measurable: ring‑down time (τ), which is inversely related to total cavity losses.

• Typical laser sources: continuous‑wave (CW) lasers or quantum‑cascade lasers for mid‑IR applications.

• Output: absolute absorption cross section → concentration (ppb/ppt sensitivity achievable with proper optics).

Applications of CRDS Cavity Ring Down Spectroscopy

• Limits, selectivity, and rapid response matter:

• Ultra‑high purity (UHP) gas monitoring for semiconductor and electronics manufacturing.

• Process gas quality control and leak detection in industrial gas plants.

• Calibration and transfer standards at national metrology institutes and laboratories.

• Environmental monitoring, breath analysis, and atmospheric trace‑gas research.

• Isotope ratio and specialized molecular spectroscopy in research applications.

Advantages of CRDS Cavity Ring Down Spectroscopy

• Exceptional sensitivity: CRDS instruments reach parts‑per‑billion (ppb) and, for selected analytes, parts‑per‑trillion (ppt) detection limits when combined with high mirror reflectivity and low noise electronics. 

• Absolute absorption measurement: Ring‑down time is a direct pathlength‑enhanced absorption metric—no external calibration gas is required for linear response (though calibration improves traceability).

• High selectivity: Laser tuning to discrete absorption lines reduces cross‑interference and enables species‑specific monitoring.

• Non‑destructive & fast: Measurement times are typically milliseconds to seconds, enabling near‑real‑time monitoring.

• Robust for production: CW‑CRDS implementations made the technique compact and cost‑effective for factory and process use. The CW approach was a pivotal step in commercial CRDS adoption. 

Technical Specifications of Tiger Optics CRDS Cavity Ring Down Spectroscopy

Our TIGER OPTICS CRDS analyzers are built for ultra‑high purity and bulk gas applications with engineering focused on sensitivity, stability, and ease of integration. Representative technical highlights:

• Sensitivity: manufacturer‑specified detection limits commonly in the low ppb to ppt range (analyte and matrix dependent). 

• Measurement speed: millisecond to second ring‑down acquisition and reporting.

• Laser source: CW diode or QCL depending on wavelength region and species.

• Optical cavity: high‑reflectivity mirrors and cavity stabilization for long‑term stability.

• Communications: standard industrial outputs (analog, Modbus, Ethernet) and integration‑ready software.

• Calibration & traceability: designed for use as transfer standards at calibration labs and national metrology institutes. 

For a complete, model‑specific table of specifications (detection limits, wavelength coverage, response time, sample handling and dimensions), download the CRDS product guide or datasheet. View our CRDS product page. 

Frequently Asked Questions (FAQs)

Is CRDS Cavity Ring Down Spectroscopy suitable for continuous process monitoring?

Yes. Modern CW‑CRDS analyzers are designed for continuous, unattended operation with fast response times and industrial communications for process control. 

What detection limits can I expect?

Detection limits depend on the target absorption cross section, matrix gas, mirror reflectivity, and instrument model. Typical TIGER OPTICS CRDS analyzers achieve low ppb to ppt‑level sensitivity for many contaminants—refer to the datasheet for model‑specific numbers. 

How does the technique handle complex gas mixtures?

CRDS is highly selective when the laser is tuned to an isolated absorption line. For overlapping spectra, multispecies fitting or alternative wavelengths can be used; in some cases a separation (e.g., GC) upstream is appropriate. 

Who advanced CW‑CRDS for commercial use?

Continuous‑wave CRDS methods were developed and championed by researchers including Kevin K. Lehmann; CW implementations were a key enabler for compact, commercial analyzers. 

CRDS Gas Analyzers (product) 
About TIGER OPTICS CRDS

Download the CRDS Datasheet or Contact Our Experts

Learn model‑level specifications, detection limits, and integration options by downloading the datasheet, or contact our applications team for a custom evaluation.

Download the CRDS Datasheet
Contact Our Experts