the probe beam reaches spectrometer 110 for the particular implementation of fig1 the probe and reference beams are recombined using the same beam splitter 108 used to cause their separation in the preferred implementation an objective 124 is placed in the reference path objectives 114 and 124 are similar as possible so that they impart the same chromatic phase retardation this arrangement is found in linnik microscopes the position of mirror 122 is controlled by a piezo actuator 126 both the piezo actuator 126 and the spectrometer operate under control of a processor 128 by changing the position of mirror 122 the length of the path traveled by the reference beam may be controlled the recombination of the probe and reference beams creates interference between the two beams changing the path length traveled by the reference beam i e moving mirror 122 modulates this interference in general it is also possible to modulate the interference pattern by varying the path length traveled by the probe beam while holding the path length traveled by the reference beam fixed this can be done for example by moving subject 112 processor 128 controls this modulation and synchronously samples the output of spectrometer 110 for typical implementations spectrometer 110 includes a photodiode or ccd array that measures multiple wavelengths simultaneously this enables processor 128 to obtain samples from spectrometer 110 that are resolved in both time and wavelength processor 128 calculates a complex reflection coefficient r k for each subject 112 that is measured r k is related to the output s k x of spectrometer 110 by the following equation s u2061 k x u222b uf603 a u2061 k u2032 u2062 r u2061 k u2032 b u2061 k u2032 u2062 e.