A laser vibrometer for measurement of ambient chemical species includes a laser that produces a beam that is split into a reference readout beam and a signal readout beam. A probe laser beam is tuned to an absorption feature of a molecular transition, and generates acoustic signals when incident on a gaseous species via the photo acoustic effect. The scattered acoustic signals are incident on a thin membrane that vibrates. The readout laser beam reflected from the vibrating membrane is mixed with the reference beam at the surface of a photo-EMF detector. Interferrometric fringes are generated at the surface of the photo-EMF detector. Electric current is generated in the photo-EMF detector when the fringes are in motion due to undulations in the signal readout beam imparted by the vibrating membrane. A highly sensitive photo-EMF detector is capable of detecting picoJoules or less laser energy generated by vibrating processes.

A laser vibrometer for measurement of ambient chemical species includes a laser that produces a beam that is split into a reference readout beam and a signal readout beam. A probe laser beam is tuned to an absorption feature of a molecular transition, and generates acoustic signals when incident on a gaseous species via the photo acoustic effect. The scattered acoustic signals are incident on a thin membrane that vibrates. The readout laser beam reflected from the vibrating membrane is mixed with the reference beam at the surface of a photo-EMF detector. Interferrometric fringes are generated at the surface of the photo-EMF detector. Electric current is generated in the photo-EMF detector when the fringes are in motion due to undulations in the signal readout beam imparted by the vibrating membrane. A highly sensitive photo-EMF detector is capable of detecting picoJoules or less laser energy generated by vibrating processes.

This N.sub.2O analysis device is provided with: a light source (11) which radiates laser light onto an exhaust gas (5) containing N.sub.2O, H.sub.2O and CO.sub.2; a light receiver (13) which receives the laser light that has been radiated onto the exhaust gas (5); a light source control unit (14a) of a control device (14), which controls the wavelength of the laser light radiated by the light source (11) to between 3.84 m and 4.00 m; and a signal analyzing unit (14b) of the control device (14), which calculates the N.sub.2O concentration by means of infrared spectroscopy, using the laser light received by the light receiver (13) and the laser light controlled by the light source control unit (14a) of the control device (14).

A laser vibrometer for measurement of ambient chemical species includes a laser that produces a beam that is split into a reference readout beam and a signal readout beam. A probe laser beam is tuned to an absorption feature of a molecular transition, and generates acoustic signals when incident on a gaseous species via the photo acoustic effect. The scattered acoustic signals are incident on a thin membrane that vibrates. The readout laser beam reflected from the vibrating membrane is mixed with the reference beam at the surface of a photo-EMF detector. Interferrometric fringes are generated at the surface of the photo-EMF detector. Electric current is generated in the photo-EMF detector when the fringes are in motion due to undulations in the signal readout beam imparted by the vibrating membrane. A highly sensitive photo-EMF detector is capable of detecting picoJoules or less laser energy generated by vibrating processes.

An optical sensor includes a sensing element and an elastic sealing component. The sensing element includes a prism including a hypotenuse face and two leg faces and a sensing film on the hypotenuse face. The sensing film is exposed to a gastight space to include the target substance. A confining wall confining the gastight space has an opening and the opening is covered with the sensing element. The elastic sealing component is located between the sensing element and the opening. The sensing element is fixed by being pressed by the fixture. Light passes through one of the two leg faces and hit the sensing film. Light reflected off the sensing film goes out through the other one of the two leg faces. The photodetector detects light that is reflected off the sensing film and comes out through the other one of the two leg faces.