Laser device coupled to a cavity by optical feedback for detecting gas traces
A device of detection of gas in trace amounts by a semiconductor laser coupled to a resonant optical cavity containing a chemical species to be analyzed. The device comprises a resonant optical cavity containing a chemical species to be analyzed; a semiconductor laser, coupled by optical feedback to the optical cavity and capable of being frequency-scanned; a means for adjusting the laser-cavity coupling rate; a means for finely adjusting the optical feedback phase; and a means for measuring the light transmitted by the cavity.
1. A device for detecting gas in trace amounts, comprising:
a resonant optical cavity containing a chemical species to be analyzed;
an optical feedback sensitive laser coupled by optical feedback to the resonant optical cavity and capable of being frequency-scanned;
a means for adjusting a laser-cavity coupling rate to provide improved laser-cavity coupling;
a means for finely adjusting the phase of the optical feedback; and
a means for measuring the light transmitted by the cavity.
2. The device of claim 1 , wherein the device comprises a means for roughly adjusting the distance from the optical feedback sensitive laser to the resonant optical cavity.
3. The device of claim 1 , wherein the means for finely adjusting the phase of the optical feedback is a means for setting a laser-cavity optical distance.
4. The device of claim 3 , wherein the means for finely adjusting the phase of the optical feedback is a mirror disposed on a piezo-electric ceramic arranged in the optical path from the optical feedback sensitive laser to the resonant optical cavity.
5. The device of claim 1 , wherein the means for adjusting the laser-cavity coupling rate is an optical attenuator attenuating the light sent back by the resonant optical cavity to the optical feedback sensitive laser.
6. The device of claim 1 , wherein the optical feedback sensitive laser is a laser diode.
7. The device of claim 1 , wherein the resonant optical cavity is of a V-shaped type, comprising a first mirror oblique with respect to a laser incidence direction, a second mirror orthogonal to the laser incidence direction, and a third mirror forming a cavity with the first and second mirrors.
8. The device of claim 1 , wherein the resonant optical cavity is a conventional two-mirror cavity.
9. A method for using the device of claim 1 , comprising the step of adjusting the ratio between a laser-cavity distance and a length of one or several arms of the resonant optical cavity to an integer.
10. A method for using the device of claim 1 , comprising the step of varying a laser-cavity optical path by a value on the order of the laser wavelength.
11. A device for detecting gas in trace amounts, comprising:
a resonant optical cavity containing a chemical species to be analyzed;
an optical feedback sensitive laser coupled by optical feedback to the resonant optical cavity and capable of being frequency-scanned;
an optical attenuator for adjusting the laser-cavity coupling rate to provide improved laser-cavity coupling;
a mirror disposed on a piezo-electric ceramic for finely adjusting the phase of the optical feedback; and
a photodetector for measuring the light transmitted by the cavity.
12. A device for detecting gas in trace amounts, the device comprising:
a resonant optical cavity containing a chemical species to be analyzed, the resonant oDtical cavity having several arms;
an optical feedback sensitive laser disposed at a distance from the resonant optical cavity and coupled by optical feedback to the resonant optical cavity and capable of being frequency- scanned;
a means for adjusting the laser-cavity coupling rate;
a means for finely adjusting the phase of the optical feedback; and
a means for measuring the light transmitted by the resonant optical cavity,
wherein the ratio between the distance and a length of one or the several arms of the resonant optical cavity is adjusted to be an integer.