Title :
Intra-Cavity Spectroscopy Using Amplified Spontaneous Emission in Fiber Lasers
Author :
Arsad, Norhana ; Li, Min ; Stewart, George ; Johnstone, Walter
Author_Institution :
Dept. of Electron. & Electr. Eng., Univ. of Strathclyde, Glasgow, UK
fDate :
3/1/2011 12:00:00 AM
Abstract :
Fiber 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 absorption spectroscopy (ICAS) which makes use of the amplified spontaneous emission (ASE) already present within a fiber laser cavity. The ASE also provides a convenient broadband source for the simultaneous interrogation of several gases within the gain-bandwidth of the fiber laser. The key principle is based on adjusting the cavity attenuation to select an appropriate inversion level where the fiber gain curve is flat. Under this condition, the ASE undergoes multiple circulations within the fiber laser cavity, enhancing the effective path-length of a gas cell placed within the laser cavity. A theoretical model of system operation is given and we have experimentally demonstrated the principle of operation with acetylene and carbon dioxide using a simple erbium fiber laser system containing a 6 cm path-length, fiber coupled, intra-cavity, micro-optic gas cell. We have experimentally simultaneously observed 16 absorption lines for 1% acetylene gas in the 1530 nm region and detected the very weak carbon dioxide lines in this same wavelength region. A path length enhancement of in the linear regime has been demonstrated transforming the 6 cm micro-optic cell into an effective path length of m. We also demonstrate how the enhancement factor may be calibrated by use of a simple fiber-optic interferometer. Apart from the OSA, all components are inexpensive and the system is very simple to construct and operate.
Keywords :
erbium; fibre lasers; gas sensors; laser cavity resonators; measurement by laser beam; spectroscopy; superradiance; Jk:Er; acetylene gas; amplified spontaneous emission; broadband source; cavity attenuation; enhancement factor; fiber gain curve; fiber lasers; gas sensors; intra-cavity absorption spectroscopy; inversion level; micro-optic gas cell; overtone absorption lines; path length enhancement; wavelength 1530 nm; Intra-cavity spectroscopy; erbium-doped fiber lasers; fiber sensors; gas sensors; laser spectroscopy;
Journal_Title :
Lightwave Technology, Journal of
DOI :
10.1109/JLT.2010.2103048