A sensitive fluid sensor for detecting fluids and particularly trace
fluids. The sensor may be adjustable for detecting fluids of various
absorption lines. To effect such adjustment, a tunable laser may be used.
The laser may be an edge emitting diode, a VCSEL or other tunable source.
The detection apparatus of the sensor may incorporate a sample cell
through which a laser light may go through. The sample cell may comprise
a tunable ring-down cavity. The ring-down cavity may be a ring laser
cavity like that of a ring laser gyroscope. There may be a photo detector
proximate to the ring down cavity connected to a processor.