Fibre laser sources offer interesting possibilities for gas sensors since they can operate over an extended wavelength range, encompassing the near-IR absorption lines of a number of important gases but a major problem is that overtone absorption lines of gases in the near-IR are relatively weak. In order to enhance sensitivity, we present here a simple method of intra-cavity laser absorption spectroscopy (ICLAS) which makes use of the amplified spontaneous emission (ASE) already present within a fibre laser cavity. The ASE also provides a convenient broad-band source for the interrogation of several gases within the gain-bandwidth of the fibre laser. The key principle is based on adjusting the cavity attenuation to select an appropriate inversion level and hence flatten the erbium-fibre gain curve. Under this condition, the ASE undergoes multiple circulations within the fibre laser cavity, enhancing the effective path-length of a gas cell placed within the laser cavity. We have experimentally demonstrated the principle of operation with acetylene gas, using a simple erbium fibre laser system containing a 6cm path-length, fibre coupled, intra-cavity, micro-optic gas cell. For 1% acetylene gas, we have experimentally observed 16 absorption lines in the 1530nm region and a path length enhancement of ~60 has been demonstrated, transforming the 6cm micro-optic cell into an effective path length of ~3.5m. Apart from the OSA, all components are inexpensive and the system is very simple to construct and operate.
|Pages (from-to)||750312-1 - 750312-4|
|Number of pages||4|
|Journal||Proceedings of SPIE: The International Society for Optical Engineering|
|Publication status||Published - 2009|
|Event||20th International Conference on Optical Fibre Sensors - Edinburgh, United Kingdom|
Duration: 5 Oct 2009 → …
- intra-cavity spectroscopy, laser spectroscopy, erbium-doped fibre lasers, fibre sensors, gas sensors