Abstract: An optical apparatus includes an optical fibre having a radiation inlet, a radiation outlet and a termination by which optical radiation is transmitted from the fibre, a retroreflector spaced from the termination and aligned with the path of radiation from the termination such that the radiation is reflected back along the same path onto the termination and the reflected radiation passes back along the same fibre to the radiation inlet.

Abstract: An infra-red liquid sampling cell has a sapphire base plate with a part-spherical concave recess. A sapphire upper plate is hinged relative to the base plate larger radius of curvature than the recess. When the upper plate is lowered into contact with the base plate its convex surface contacts the liquid sample thereby excluding air bubbles and, when in contact with the edge of the recess, produces a well-defined sample thickness. An infra-red source directs radiation down through both plates and the liquid sample to a detector.