Terahertz pulsed spectroscopy method

A method of investigating an object 94 comprises the steps of irradiating the object with an optically-generated pulse of electromagnetic radiation 90, said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz and detecting radiation transmitted and/or reflected from a first point on or within the object to obtain a time domain waveform, wherein the irradiating pulse of radiation is focused at a second point on or within the object such that a diffuse terahertz irradiating beam 96 probes the sample. Apparatus for investigating an object by irradiating a plurality of points on the object and combining time domain waveforms from each of the points to produce a time domain waveform for the object which has been averaged over the plurality of points, and a method of separating a portion of the detected radiation which corresponds to directly transmitted or reflected radiation and applying a Fourier transform to the remaining portion of the detected radiation are also disclosed.