A portable CLaDS instrument has been deployed for the environmental monitoring of nitrous oxide at Princeton University (invention partners). This proved the instruments enhanced properties over other traditional sensors, and shows outstanding performance in terms of sensitivity, robustness and reliability of results.

A table –top instrument is currently being built at the STFC (Oxford) to demonstrate the technique’s capabilities with methane and ultimately to find partners to develop products at target applications. A custom spectrum analyser specified for CLaDS is in development that will aid the further miniaturisation of the instrument. The likely finish date of this instrument is July 2013.






CLaDS is a new spectroscopic technique that is capable of real-time, sensitive and selective trace gas analysis. It is based on a different principle to than other optical gas sensing methods available today. Standard laser-based technologies determine concentration of the molecule by measuring how much light is absorbed by the gas sample at different wavelengths. CLaDS performs sensitive detection by measuring changes in refractive index of the sample generated by the target molecules.

Existing instruments in the market are fundamentally limited by the absorption technique. This technique presents several draw-backs:

  • Relies on a measurement of a small change of light intensity on top of a large background. The background intensity fluctuates as a result of the environment; turbulence, soot, water vapor, etc. This limits the instrument’s capabilities in terms of sensitivity, selectivity and reliability.


  • There is a non-linear dependence of the absorption on sample concentration. Therefore over a given concentration the instruments give null results.


To overcome these limitations, industries that require sensitive and flexible instrumentation use more expensive and bulky techniques. Most notably Gas Chromatography (GC) that offer high sensitivity and a linear response over the full concentration range of gases. However these instruments are very expensive (~100k) and bulky, thus limiting their application in the field. Furthermore GCs require dedicated staff members and time consuming sampling procedures that prohibit real time analysis.

CLaDS overcomes the fundamental limitations of absorption techniques and thus offers users several advantages and a unique capability offering.



Sensitive detection is performed by measuring changes in refractive index of the sample generated by the target molecules, rather than measuring the amount of light absorbed by the sample.



  • High sensitivity (parts per billion (ppb) / parts per trillion (ppt))

  • Immunity to detected power fluctuations (thus high immunity to demanding environments (soot, water vapor, temperature)

  • Linear response over the full concentration range (0 –  100%)  of the target molecule.

  • Fast response (frozen atmosphere) allowing reliable results in turbulent environments

  • Small and robust. CLaDS is made up of relatively few components with no moving parts and low power consumption – allowing it to be portable and thus applied in field deployment.



The improved performance is provided using only off-the shelf components (not different from what is used in current systems) and very simple inexpensive electronics for signal processing. This is important for further commercialisation of CLaDS since the market is more likely to accept solutions that are well known and can be trusted in terms of hardware availability and reliability.




Defence / Military and Law Enforcement

  • Identification of hazardous materials

  • Chemical weapons, explosives and their precursors

Automotive Industry

  • Analysis of car exhaust gases

Manufacturing Industry / Power Generation

  • Continuous monitoring of greenhouse gas emission

  • Assessing process efficiency (by analysing exhaust gases)

  • Analysis of headspace gases in pipes and barrels

  • Semiconductor device manufacture exhaust gases

Environmental Protection

  • Atmosphere monitoring (pollution)

  • Crop monitoring (e.g. ground cover, soil chemistry)

Medical Diagnostics

  • Breath testing for various diseases


  • Astronomical study of atmospheres

  • Monitoring of chemical reactions


Patent Information:
Country Serial No.
United States 13502039
Japan 538401/2012
India 908/MUMNP/2012
European Patent Office 10787861.3
China 201080050338.8
For Information, Contact:
Elizabeth Bain
IP Manager
STFC Innovations
+44 (0) 1925 60 3680
02.c. Process control and logistics
03.a. Other Industrial Technologies
03.b. Process Plant Engineering
06.a. Medicine, Human Health
09.a. Measurement Tools
09.c. Electronic measurement systems
10.b. Environment