PSA Toolbox

The confluence of optical interferometry and digital data processing in the 1970's gave rise to phase-shifting interferometry, which is now widely used in a range of techniques for measuring the form of precision surfaces and components. The digital detection with linear charge-coupled device (CCD) array detectors and computer processing of interferometric irradiance maps (fringes) has enabled phase measurements with uncertainties close to 2π/1000. In phase-shifting interferometry using a two-beam interferometer, a set of irradiance maps is measured and between each measurement the phase between the two beams is incremented (shifted) by a known, constant amount. The phase difference between the two beams at each detector pixel can then be calculated from the set of sampled intensity measurements. This discovery has resulted in a large body of work on improved phase-shifting algorithms (PSA) for phase measurements. This toolbox aids the design of new phase measuring algorithms with properties tailored for specific applications. It is also useful to analyze existing phase shifting algorithms. The toolbox consists of worksheets for the wxmaxima interface to Maxima, the open source computer algebra software.

Example: Sensitivity (blue) and Phase Response (green) of the Schwider-Hariharan Algorithm