Optical fiber gas sensor based on thermal lens spectroscopy instrument composed of spherical lensed fibers

This paper describes the performance of an optical fiber gas sensor based on thermal lens (TL) spectroscopy. This sensor features an optical absorption path whose length is extremely short compared with other optical spectroscopic techniques. A prototype of a robust sensing head is proposed whose sensitivity is demonstrated. An all-fiber TL gas sensor system built with a fiber ring laser is proposed as a method of dramatic sensitivity enhancement, and its capability is certified.