Patent ID: 7208737

Claim:
A photoacoustic detector, comprising at least a first chamber suppliable with a gas to be analyzed, a window for letting modulated and/or pulsed infrared radiation and/or light in the first chamber, a second chamber, which constitutes a measuring space with a volume V and which is in communication with the first chamber by way of an aperture provided in a wall of the first chamber, at least one sensor, which is arranged in the wall aperture of the first chamber and adapted to be movable in response to pressure variations produced in the first chamber by absorbed infrared radiation and/or light, and means for measuring the sensor movement optically by using an interferometer comprising at least a light source, a reference mirror, a beam splitter or a semi-transparent mirror for splitting the beam for the sensor and for the reference mirror of the interferometer, and at least three detectors for receiving light beams coming from the beam splitter, wherein the interferometer is arranged to provide at least three measuring signals in different phase relative to each other.