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Home > Products > Gas Analysers > Extractieve lasers > Cavity Ring-Down Spectroscopy


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Principle: Laser TDL

Cavity Ring-Down Spectroscopy (CRDS) works by attuning light rays to the unique molecular fingerprint of the sample speciesCavity Ring-Down Spectroscopy

Cavity Ring-Down Spectroscopy (CRDS)

Detection at the Speed of Light

Based on absorption spectroscopy, 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.

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.

How It Works:

  1. A Continuous Wave (CW) diode laser emits a directed beam of light energy through an ultra-high reflective mirror into the absorption cell (cavity).
  2. The light reflects back and forth between two ultra-high reflective mirrors multiple times, up to a total path length of 100 kilometers.
  3. Once the photodiode detector “sees” a preset level of light energy, the light source is shuttered or diverted from the cavity.
  4. On each successive pass, a small amount of light or ring-down signal emits through the second mirror and is sensed by the light detector.
  5. Once the light "rings down", the detector achieves a point of zero light energy in milliseconds, and the measurement is complete.


The key components illustrated are as follows:

  1. Diode laser: Emits light energy
  2. Isolator: Prevents light energy feed-back from interfering with the laser Acousto-Optical
  3. Modulator: Shuttering device for the light source
  4. Absorption Cell: With mirrors, creates measure-ment cavity
  5. Photodiode: Monitors the light energy from the absorption cell
  6. Trigger: Works in concert with the photo-diode and sends signal to the AOM to activate the ring-down cycle.


  1. 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.
  2. It tunes back to the absorption peak to determine the τ value, dependent on the sample species concentration.
  3. The concentration of the sample species is directly calculated using the above equations.
  4. Based on Beer’s Law, this value constitutes an absolute measurement and is unaffected by losses outside the ring-down cavity.


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.


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Serani Software

Tiger Optics’ Serani™ Analyzer Interface Software offers users a new way to access their analyzer remotely from any computer or laptop. 

Spark platform

The Spark is the lowest cost CRDS analyzer on the market, offering powerful performance on a budget, plus the highest range (5 orders of magnitude!) and fastest speed of any Tiger analyzer! Available for detection of H2O and other molecules in a variety of matrices, the Spark is ideal for cylinder analysis in industrial and medical gases, and many other applications. 


The CO-rekt allows the use of Tiger's powerful CRDS technology in harsh industrial environments. Outfitted with a purged enclosure, the CO-rekt meets Class I, Div 2 specifications for use as CO, H2O, CH4 and CO2 analyzer in SMR and HyCO processes, among others.

HALO Platform

The HALO is our most versatile analyzer, with a perfect blend of high performance, compact footprint, and cost efficiency. The HALO is used to analyze an enormous variety of gases, including hydrides, fluorides, rare gases, and more. 

LaserTrace System

The LaserTrace is our most powerful trace gas analyzer with detection limits as low as 50 ppt, capable of measuring four molecules at a time on up to four separate lines. The system is the semi industry standard to monitor H2O, CH4 and O2 in bulk gases, but is also available for many other molecules and applications.

Prismatic 2

The Prismatic 2 is a multi-species analyzer capable of monitoring up to four trace molecules in a single gas stream. It is an ideal solution for applications that require the simultaneous analysis of multiple analytes in real-time, for instance, quality control of fuel-cell grade hydrogen or monitoring of unmanned ASUs.

Tiger-i platform

For environmental monitoring and analysis in ambient air, Tiger Optics packages Cavity Ring-Down Spectroscopy in the compact, watchful Tiger-i. 

Aloha H2O series

The ALOHA H2O series offers the world's best detection limits for moisture in ammonia (as low as 2 ppb). Ultra-pure ammonia is a critical building block for the manufacture of HB LEDs and for advanced GaN on Si devices.

Ankersmid engineers, delivers and performs service on analysis equipment, to complete CEM systems and process systems in associated analysis houses. They are used in industrial process technology, laboratories, air force, stable technology and biogas installations

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