Frits Zernike - Research in Physical Optics

Research in Physical Optics

In 1930, Zernike was conducting research into spectral lines and discovered that the so-called ghost lines that occur to the left and right of each primary line in spectra created by means of a diffraction grating, have their phase shifted from that of the primary line by 90 degrees. It was at a Physical and Medical Congress in Wageningen in 1933 that Zernike first described his phase contrast technique in microscopy. He extended his method to test the figure of concave mirrors. His discovery lay at the base of the first phase contrast microscope, built during World War II.

Another contribution in the field of optics is related to the efficient description of the imaging defects or aberrations of optical imaging systems like microscopes and telescopes. The representation of aberrations was originally based on the theory developed by Ludwig Seidel in the middle of the nineteenth century. Seidel's representation was based on power series expansions and did not allow a clear separation between various types and orders of aberrations. Zernike's orthogonal circle polynomials provided a solution to the long-standing problem of the optimum 'balancing' of the various aberrations of an optical instrument. Since the 1960s, Zernike's circle polynomials are widely used in optical design, optical metrology and image analysis.

Zernike's work helped awaken interest in coherence theory, the study of partially coherent light sources. In 1938 he published a simpler derivation of Van Cittert's 1934 theorem on the coherence of radiation from distant sources, now known as the Van Cittert-Zernike theorem. He died in hospital at Amersfoort, Netherlands in 1966 after suffering illness the last years of his life.