External Cavity Laser Spectrometer

Scientists at STFC have developed a novel external cavity laser absorption spectrometer, which can be used to determine characteristics of sample such as environmental air, human or animal breath, environmental water or condensate from gas, bodily fluids, etc.





The apparatus has an external cavity semiconductor laser with a semiconductor gain medium within optical resonator. The absorption cell is arranged such that a portion of sample in the cell is coupled with gain medium and a controlled injection current is applied to the gain medium. A photo detector is provided to detect laser light output by semiconductor laser. The laser output is then analysed to determine characteristics of the sample.

The sample gives rise to a loss rate of photons generated in the gain medium. The characteristics of the sample can be determined from a reduction in photon lifetime of the external cavity laser in the presence of the sample. The external cavity being conveniently provided with a tuning element so that the resonant frequency of the external cavity laser can be tuned to or scanned across wavelengths, characteristics of the sample can be determined across the scanned range of wavelengths.



  • Increased sensitivity to absorption characteristics can be achieved by varying the injection.
  • The characteristics can be determined at multiple wavelengths.
  • Improved stability and sensitivity.
  • Improved reproducibility.
  • Reduced frequency of calibration.



  • Environmental monitoring
  • Medical diagnostics
Patent Information:
Country Serial No.
Patent Cooperation Treaty PCT/GB2013/052138
United States 14/422924
For Information, Contact:
Elizabeth Bain
IP Manager
STFC Innovations
+44 (0) 1925 60 3680
01.h. Imaging & Detector Technology
05.e. Meteorology/Climatology
05.f. Physics
06.a. Medicine, Human Health
10.b. Environment