167882 ⎘
Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light; Systems in which incident light is modified in accordance with the properties of the material investigated; Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle; Dip refractometers, e.g. using optical fibres comprising optical fibres with an unclad part on the fibre