Multi-species gas detection with long-wavelength VCSEL

A long-wavelength VCSEL has been used for the first time for multi-species gas detection and for trace gas sensing. The VCSEL with a buried tunnel junction (VERTILAS, Germany) was capable of covering a spectral range of 7 nm or 28 cm(-1) (central wavelength at 1576.3 nm) with the laser temperature and injection current varied between 0-50 degreesC and 0.5-5 mA respectively. The pressure Of CO:CO2=3:2 gas mixtures buffered with N-2 (N-2 content 0 - 90 %) was varied from 1 mBar up to I Bar. To avoid a non-linear dynamic tuning, the combination of a direct injection current with a saw-tooth waveform was used to sweep the laser frequency across absorption lines. A LabVIEW-based computer code was developed for multispecies gas analysis in time domain. Absorption spectra were averaged over 10(2) - 10(3) laser scans. It has been shown that a cross interference from all collisional partners should be taken into account for accurate multi-component gas detection. A concentration of 600 ppm of CO2 in atmospheric air (fractional absorption - 104) was detected with laser output power of 120 muW. Long-wavelength VCSELs can be used both for multi-species gas detection in a wide range of pressures and for trace gas monitoring.