Abstract: The present invention provides a method of analysing an object (29) (for example a wive or a steut), comprising the steps of: (a) irradiating the object with a Terahertz pulse of electromagnetic radiation, such that a portion of the irradiating radiation couples to the object as a surface wave; (b) detecting radiation reflected and/or scattered from the object to obtain a time domain waveform; (c) extracting the parts of the radiation detected in step (b) relating to the surface wave on the object and (d) analysing the radiation identified in step (c) in order to derive information relating to a physical characteristic (for example the thickness of a coating) of the object.

Abstract: An apparatus for investigating a sample comprising: a source of beam radiation; a detector for detecting a beam of radiation reflected by the sample and an optical subsystem for manipulating the beam between source and detector wherein the optical subsystem comprises a first optical element arranged in use to angularly deflect the source beam within a given solid angle and a second optical element arranged to focus the beam from the first optical element onto a substantially flat image plane and wherein radiation reflected by the sample passes back through the first and second optical elements to the detector.

Abstract: An emitter for emitting radiation in a first range of frequencies comprising: a photoconductive material (11); and first and second contact elements (12, 13, 14) separated by a photoconducting gap provided by said photoconducting material (11), for applying a bias across said photoconducting gap, wherein at least one of said first and second contact elements (12, 13, 14) comprises a resistive element (14) for restricting current flow between said first and second contact elements in a second range of frequencies lower than the first range of frequencies.

Abstract: An apparatus for varying the path length of a beam of radiation, the apparatus comprising: an element (51) rotatably mounted about an axis, said element comprising two reflective surfaces in fixed relation to one another such that radiation may be reflected between said reflective surfaces and out of the element (51); and driving means (55) for rotatably oscillating said element about said axis.