Frits Zernike was born on July 16, 1888, in Amsterdam, the son of two mathematicians, Carl Frederick August Zernike and Antje Dieperink Zernike. While still young, Zernike was recognized for his mathematical abilities. He received both his B.S. and his Ph.D. in physics from the University of Amsterdam, and he worked at an astronomical laboratory while pursuing his graduate studies. His doctoral thesis, "Critical Opalescence, Theoretical and Experimental," quickly established him as a leader in his field. In 1915 he was appointed lecturer in theoretical physics at the University of Groningen. In 1920, he was promoted to professor, and he remained at Groningen for the rest of his career.
It was while working in the field of astronomy that Zernike first discovered the advantages of phase-contrast techniques. Irregularities on the surfaces of the curved mirrors of telescopes were a common problem at that time; these mirrors sometimes produced "ghost" images and Zernike hypothesized that they were caused by out-of-phase wavelengths. If he could somehow bring direct and diffracted images back into phase, perhaps these aberrations would disappear. He developed a glass plate with tiny grooves etched in it to be placed in the focal plane of the telescope, and he called this a "phase plate." His experiment worked: when looking through the phase plate, the out-of-phase areas became clearly visible. Zernike published these findings in 1934, and by 1935 he was applying these same principles to microscopes, which he knew had optical problems that were similar to telescopes. He inserted a phase strip into the focal plane of a microscope and immediately it brought the direct and the diffracted beams into phase.
Although the practical applications of Zernike's findings seem obvious now, it was some years before he could find a manufacturer for a phase-contrast microscope. He first approached a German company, Carl Zeiss, in 1932. "They understood the theoretical background but did not think the practical use would be great," Zernike recalled in an interview when he won the Nobel Prize. "They said if it was practical they already would have developed it." Finally, in 1941, Carl Zeiss agreed to produce the instrument. But it was not until American troops arrived in Germany in 1945 and discovered photomicrographs taken by a phase-contrast microscope that Zernike's instrument received worldwide attention. When he won the Nobel Prize in 1953, the phase-contrast microscope was cited as being a key to insights into cancer research.
Unlike many instrument makers, Zernike worked first from theoretical principles and then moved to practical applications, blending theory with experiment. Though the phase-contrast microscope is considered his crowning achievement, Zernike is also known for other work. Early in his career he invented the Zernike galvanometer, an instrument used to detect and measure small electrical currents. The Zernike polynomials are a method he developed regarding the wave theory of light and are widely used by mathematicians. He also made many improvements in infrared and ultraviolet spectroscopy, as well as in the construction of the .
Although Zernike stayed at his alma mater for his entire career, he was a visiting professor of physics at the Johns Hopkins University in Baltimore in 1948. In 1950 he was elected to the Royal Microscopical Society of London, and he was presented with the Rumford Medal of the British Royal Society in 1952.
Zernike married Dora van Bommel van Vloten in 1929. The couple had two children; his wife died in 1944. In 1954, Zernike remarried, to L. Koperberg-Baanders. He retired in 1958 and died in Groningen on March 10, 1966.
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