Abstract: An infrared temperature probe for high pressure use is in the form of a hollow bolt adapted to be threaded into a complementary threaded aperture in the wall of a pressure vessel with the end thereof disposed flush with the internal surface of the pressure vessel wall. An infrared transparent window is secured in the end of the hollow bolt with one surface thereof disposed flush with the end of the bolt. A bundle of optical fibers is secured within the opposite end of the hollow bolt and a glass rod is mounted within the hollow bolt in operative relation to the window and the optical fiber bundle for transmitting infrared radiation from the window to the optical fiber bundle. The interior of the hollow bolt may be supplied with a circulating cooling liquid or gas.

Abstract: A band-ratio radiometer is disclosed which makes use of either a bifurcated or trifurcated fiber optic bundle, over two branches of which the sample radiation is transmitted in different wavelength regions. The third branch may be used to provide illumination of the target area, for aiming purposes, by injecting light at the near end of this branch. By this means, the remote ends of all three bundles may be focussed precisely upon the target area, with no parallax problem. The system avoids the use of conventional optical filters by making use of detectors which are identical in wavelength sensitivity and optical fibers which differ in wavelength transmittance.