Patent ID: 7777187

Claim:
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 for receiving a probe beam, the probe beam having a phase related to the phase of the beam of radiation irradiating the sample; a delay line being operable to vary the relative path lengths of the probe beam and the beam of radiation irradiating 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 scan the source beam through a plurality of angles 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, wherein radiation reflected by the sample passes back through the first and second optical elements to the detector, and wherein the detector is configured to detect radiation reflected at varying depths within the sample by varying the relative path lengths of the probe beam and the beam of radiation irradiating the sample using the delay line.