Enhanced Detection of Gas Absorption Using an Erbium-Doped Fiber Ring Laser

Abstract

We demonstrate gas sensing using a fiber ring laser composed of an erbium-doped fiber as the laser medium and a compact gas cell module. Acetylene absorption at 1.5 m is enhanced by an intracavity configuration, in which multiple band-pass filters are used to control the wavelength of laser oscillation. A maximum enhancement factor of about 80 is achieved with an 18.3 mm cell under a pressure range below 100 Pa. Experimental results can reasonably be explained by a ring laser theory that describes the influence of acetylene pressure on the threshold and slope efficiency of the laser output characteristics.

Gas Sensing Technique Based on Fiber Laser Built-in Thermal Lens Spectroscopy Sensor

“…Recently, to overcome this problem a gas sensor using a fiber ring laser has been proposed that uniquely and effectively enhances sensitivity because the laser cavity virtually expands the path length of optical absorption. 7) In contrast, our earlier work proposed an optical fiber gas sensor based on a thermal lens (TL) spectroscopy technique. 8,9) One feature of our sensor is that the optical absorption path is much shorter (usually 20 -50 mm) compared with other optical spectroscopy techniques.…”

“…However, it was certified in similar reserch that the oscillation frequency shift problem exists when the optical absorption of gas occurred remarkably on the inside of a laser cavity. 7) Because of this, it is difficult to continually capture the optical absorption spectrum of gas, thereby resulting the sensitivity lowering. The dotted lines in Fig.…”

Thermal Lens Spectroscopy Gas Sensing Based on Etalon-Stabilized Wavelength Sweep Technique for Fiber Ring Laser

“…4) From these standpoints, the replacement of a wavelengthtunable laser diode with a fiber ring laser is indeed important. 9) Recently, to overcome these problems, a gas sensor using a fiber ring laser has been proposed to uniquely and effectively enhance sensitivity by virtually expanding the path length of the optical absorption using the laser cavity. 9) In contrast, in our earlier work, we proposed an optical fiber gas sensor [based on thermal lens (TL) spectroscopy, [10][11][12] ] which is a recognized technique for detecting with high sensitivity the impurities included in such materials as liquids and gases in a laboratory.…”

“…This problem was also confirmed in similar research. 9) For these reasons, it is difficult to continually capture the optical absorption spectrum of a gas, resulting in reduced sensitivity and reproducibility.…”