Superimposing the waves diffracted from two similar hot and cold wires provides the temperature profile around the hot one.

When two similar small objects that are installed in the arms of a Mach-Zehnder interferometer are illuminated in such a way that the image of one object in the second beam splitter is located on the other object, the diffracted waves from the objects are exactly superimposed in the interference field. The superimposed diffraction patterns disappear for a phase difference equal to an odd multiple of pi. The phase change induced by imposing changes on the medium surrounding one of the objects can be determined very accurately only by measuring the intensity distribution that appears on the superimposed diffraction patterns. Using this technique we have determined the temperature profile around a wire of diameter 0.26 mm carrying different electric currents by evaluating the phase changes at 700 points on the superimposed diffraction patterns to the accuracy of pi/200. This technique allows us to eliminate the effect of light diffraction from the geometry of an object, to measure the amplitudes of the interfering diffracted waves accurately, and to evaluate the phase difference of the diffracting waves reliably.