Cavity Ring-Down Spectroscopy 

CRDS Technology Leaders

Unmatched Measurement Speed, Quality and Reliability 

A breakthrough discovery by Professor Kevin Lehmann, Ph.D., of Princeton University made the commercialization of this technique possible.  He proved that compact, relatively inexpensive, and widely available Continuous Wave (CW) lasers can substitute for the costly, cumbersome pulsed lasers previously used in CRDS-based research.  He thereby made the requisite power of light affordable and practical for commercial use.

Based on absorption spectroscopy, our Tiger Optics’ Cavity Ring-Down Spectroscopy (CRDS) works by attuning light rays to the unique molecular fingerprint of the sample species. By measuring the time, it takes the light to fade or “ring-down”, you receive an accurate molecular count in milliseconds. The time of light decay, in essence, provides an exact, non-invasive, and rapid means to detect contaminants in the air, in gases, and even in the breath.

Ideal CRDS Applications

  • Bulk gas continuous quality control (CQC) monitoring; pre- and post-purifier trace impurity measurements
  • Quality monitoring for process specialty gases
  • Real-time monitoring for trace H2O and HF in semiconductor process equipment
  • Next-generation trace gas analyzers for detection and continuous monitoring with our APIMS for airborne molecular contaminants in semiconductor cleanrooms

Cavity Ring Down Spectroscopy Technology Delivers Detection at the Speed of Light

Process Insights_Cavity Ring-Down Spectroscopy
Process Insights_Tiger Optics CRDS analyzer
principle of CRDS technology


  • The computer-controlled system tunes the laser off the absorption peak for the sample species to determine the τ empty value, equivalent to a zero-baseline correction.
  • It tunes back to the absorption peak to determine the τ value, dependent on the sample species concentration.
  • The concentration of the sample species is directly calculated using the above equations.
  • Based on Beer’s Law, this value constitutes an absolute measurement and is unaffected by losses outside the ring-down cavity.
key components of CRDS


  • Diode laser or QCL: Emits near-IR or mid-IR light
  • Isolator: Prevents light energy feedback from interfering with the laser
  • Acousto-optic Modulator (AOM), optional: Shuttering device for the light source
  • Absorption cell with mirrors: Creates optical cavity where the gas is measured
  • Photodiode: Monitors the light energy from the cavity
  • Trigger: Works in concert with the photodiode and sends signal to the AOM or another shuttering device to start the ring-down event.
CRDS ring_decay


This graph depicts the concept of ring-down decay within the cavity after the laser source is shuttered. As the laser light bounces back and forth between the ultra-high reflective mirrors, the sample species absorbs the light energy until it’s all gone.

Our CRDS Technology

In 2001, our Tiger Optics CRDS gas analyzers were the first commercial Cavity Ring-Down Spectroscopy (CRDS) analyzers available on the market.  Today, our Tiger Optics CRDS gas analyzers monitor thousands of critical points for industrial and scientific applications. They serve the world’s national metrology institutes, where they function as transfer standards for the qualification of calibration and zero gases.

Questions? We’re here to help.