Abstract: A measuring apparatus provides data relating to the shape of an input radiation wavefront, the wavefront shape being describable at a pre-determined location in an optical system. The apparatus includes an aberration device which provides an aberration to the input radiation wavefront, the shape of which is defined by a filter function that is complex valued and has non-mixed symmetry, and a detector having a radiation sensitive surface capable of detecting the intensity of incident radiation on the surface, the detector being coupled to an output device that provides a measure of the intensity of the incident radiation. The aberration device is configured to act on an input wavefront shape to produce first and second output radiation signals that are detected by the detector and in combination cause the output device to provide data indicating an extent to which the wavefront shape is non-planar.

Abstract: A sensor system in an interferometric arrangement has a sensor arm and a reference arm. The reference arm is in a stable environment and the sensor arm is arranged to be subject to variations in strain and/or temperature. Radiation from a broadband source propagates through the arrangement and a broadband interferogram is generated as an air gap is scanned. The interferogram is recorded on an oscilloscope and analyzed using signal processing software on a computer. From the analysis the changes in group delay and optical dispersion of the light in the sensor arm due to strain and temperature changes is measured, and values for the strain and/or temperature changes calculated. A narrowband light source may be used for accurate calibration of path length differences during scanning. The strain and temperature on the sensor arm may be calibrated or tested using clamps and a thermal enclosure.