Abstract: An apparatus for detecting changes in chemical or physical parameters, comprises a sensing optical fibre having a core surrounded by a relatively sensitive cladding the absorption spectrum of which varies with changes in chemical or physical parameters when these are applied to the cladding, and a transmissive optical fibre having a core surrounded by a relatively insensitive cladding for connecting at least one end of the sensing optical fiber to a remote light source and a remote detector. The core of the sensing optical fibre has substantially the same diameter as the core of the transmissive fibre and the refractive indices of both the relatively sensitive and the relatively insensitive claddings are less than the refractive indices of the cores of both the sensing optical fibre and the transmissive optical fibre.

Abstract: For detecting changes in chemical or physical parameters an optical fibre core has bonded to its surface a chromophore responsive to the parameter. The core preferably has a porous surface with the chromophore coating extending into the porous structure.

Abstract: Laser scanning apparatus for monitoring gaseous pollutants uses two intersecting scanning beams so that the point of intersection (which is monitored by both scanning beams) can be identified by triangulation.

Abstract: Laser scanning apparatus for the monitoring of gaseous pollutants (e.g. on a chemical plant) in which two laser beams having different wavelengths (one corresponding to an absorption line of the gas to be monitored) and modulated at different frequencies are combined into a single scanning beam. A portion of the scattered radiation is collected, detected and measured to give, for each chosen beam direction, the amount of the gas being monitored. The amount of radiation reaching the detector from the laser source is varied according to a predetermined programme or in response to an external stimulus, and by this means the detector can be protected against severe overload when the beam scans over positions of abnormally high reflectivity.

Abstract: Apparatus for monitoring gaseous pollutants (e.g. on a chemical plant) produces two infra-red laser beams having different wavelengths (one corresponding to an absorption line of the gas to be monitored, the other being a reference) which are modulated with different frequencies or phases, and then combined into a single scanning beam. The scanning beam is continuously displaced angularly so as to scan the area to be monitored. A portion of the beam is returned to the apparatus by scattering or reflection, and is measured. By correlating this with the direction of the beam, a plan of the monitored area superimposed with a continuously updated indication of the amount of gas can be displayed e.g. on a VDU.