Abstract: An optical absorption gas sensor includes a radiation source, detector and radiation guide which has a rectangular cross section and curves around a side of the cross section. Locating elements locate a support element relative to the radiation guide to align the radiation source and detector with the guide. Radiation from the reference radiation source may be transmitted through a transparent measurement radiation source. Radiation from a reference radiation source may be directed around the measurement reference source. A light emitting diode may generate radiation which is detected by a photodiode and the photodiode may be driven to generate radiation having a different emission spectrum detectable using the light emitting diode, in another operating mode. Two or more abutting L-shaped radiation guide portions may form the radiation guide.

Abstract: An optical absorption gas sensor includes a radiation source, detector and a radiation guide. The radiation source and detector are close together and in thermal communication. The radiation guide has a rectangular cross section and curves in a first sense, around an axis parallel to the major dimension of the rectangular cross section, and then in a second opposite sense, and again in the first sense. A relatively long path for radiation is provided in a compact device, without the attenuation of radiation which would occur if the radiation guide did not have a rectangular cross section and curved only around an axis parallel to the major dimension of the rectangular cross section. A reference measurement can be obtained by mounting a reference radiation source behind a translucent measurement radiation source and directing radiation from the reference radiation source through the measurement radiation source.

Abstract: An optical component having a protective layer provided on a surface thereof, the protective layer preventing the component from being damaged by high velocity impacts from small particles or water droplets. The protective coating comprises a layer of gallium phosphide deposited onto the component surface using plasma assisted chemical vapour deposition (PACVD), an intermediate layer of PACVD boron phosphide, and an outer layer of PACVD diamond-like-carbon.