Patent ID: 6876450

Claim:
A laser absorption spectroscopy type gas detecting device comprising: a housing having a light transmitting portion; a light source device which is disposed within the housing and which emits through the light transmitting portion a laser beam containing a light component having a wavelength corresponding to an absorption spectrum of a gas to be detected; a concave mirror which is disposed within the housing and which has a reflecting surface that reflects the laser beam on a predetermined condensing position, after the laser beam has been reflected by a material body outside the housing and returned into the housing via the light transmitting portion; a light receiver which is adapted to be disposed at a position within the housing at the condensing position, and which outputs an electric signal to detect whether the gas to be detected is present in a vicinity of the material body, in accordance with a degree of damping of the light component having the wavelength corresponding to the absorption spectrum of the gas to be detected, by receiving the laser beam which returns via the light transmitting portion; a visible light source which is adapted to be disposed at a position within the housing at the condensing position and which by emitting visible light toward the concave mirror: (i) emits the visible light to the exterior via the light transmitting portion on a path in an opposite direction of the laser beam reflected by the material body and returning via the light transmitting portion, and (ii) forms a predetermined image which can be visually confirmed on the material body; and moving means for moving the positions of the light receiver and the visible light source so as to be interchanged.