Statistics and numerical methods in BASIC for biologists

This disclosure depicts methods and apparatus for detecting minute phase variations on reflective or transmissive specimens. A scanning phase profilometer is depicted which includes means for producing from a coherent input light beam a set, here shown as a pair, of distinguishably coded interrogating beams which are focused and scanned across a specimen as a pair of slightly displaced light spots. The interrogating beams are recombined after interaction with the specimen. Phase demodulating means are provided including a light responsive means in the path of the recombined interrogating means for detecting phase variations between the interrogating beams caused by optical path length variations as the beams are scanned across the specimen. Means are provided for producing an electrical phase differential signal characterizing the detected phase variations and electrical integrating means for integrating the phase differential signal to produce a signal characterizing the phase profile of the scansion across the specimen. Methods and apparatus for producing a two-dimensional display of the phase profile of a specimen are also disclosed.