....Optics Highlights

VII. Optics, Electromagnetic Waves & Quanta

The union of electromagnetic theory with optics began when Maxwell found that his equations for the electromagnetic field (1873) described waves traveling at the velocity of light and with the demonstrations in 1885-1889 by Hertz that electromagnetic waves were refracted and reflected like light waves. The final mathematical identification of optics with electromagnetics was achieved by Luneburg in 1944. The fusion of optics and atomic physics began in 1818 with Josef Fraunhofer and his studies of the absorption lines of the elements, leading through Plank's energy quantumization in 1900 and Einstein's analysis of the photoelectric effect to the quantum theory of atom structure proposed in 1913 by Niels Bohr, the development of quantum mechanics, and the principle of wave-particle duality of light and matter announced by Bohr in 1928.
James Clerk Maxwell (1831 - 1879) was abused after his mother died when he was nine by a tutor who thought him stupid and then, at Edinburgh Academy, was seen as a nerd who preferred his books and was nicknamed "dafty". He graduated from the University of Edinburgh and went on to Cambridge. Maxwell was not accorded the honors, during his lifetime, that his many contributions and present rank in science would seem to have warranted. In part this was because contemporary scientists did not generally accept his theory of electromagnetism; Maxwell’s mathematics was not understood and his explanation of displacement current was confusing. In England, it was supported only by a small circle of young scientists. In Germany, however, the theory attracted the support of the leading scientist, von Helmholtz, who 1879, the year in which Maxwell died unexpectedly, and fifteen years after the publication of the theory, offered a prize for its experimental verification. (Ironically, in 1880 David Hughes, the American inventor of the microphone, came to London to demonstrate to Kelvin and Stokes, who did not accept the Maxwell theory, that he could receive signals from a spark transmitter at distances of 800 yards. They told him it could be understood on the basis of induction and he went home discouraged.)
Heinrich Rudolf Hertz (1847 - 1894) came from a cultured, well-to-do Hamburg family. He first intended to become an architect but was drawn into science and received his doctorate in Berlin as the protegé of von Helmholst who set him to work in electromagnetism. Between 1885 and 1889, as a professor of physics at Karlsruhe Polytechnic, he succeeded in designing a detector and an oscillator able to produce wavelengths short enough that he could demonstrate standing waves, reflection and refraction in the laboratory, showing that the wave properties were the same as those of light, and thus substantiating that light waves are electromagnetic radiation obeying the Maxwell equations. During the course of these experiments, Hertz discovered the photoelectric effect.
Rudolf Karl Luneburg (1903 - 1949), was born in Germany, received his doctorate at Gottingen, and emigrated to the United States in 1933. He held a variety of short time university appointments and worked for American Optical during 1938-45. In 1944, he gave a summer course at Brown, distributing mimeographed notes to students and sending copies to various university libraries (including Maryland). Five years later, Luneburg was killed in an automobile accident. Then, over the years, it was realized that his notes contained much more than an exposition of previous knowledge. For example, they contained the first systematic development of ray and diffraction optics from Maxwell’s equations. In what seems a last irony, when the notes were published as a posthumous book, the publisher misspelled Luneburg's name.
Joseph von Fraunhofer (1787 - 1826), apprenticed to a glass polisher by his father, a poor Bavarian glazier, was buried in and then rescued from the collapsed ruin of his master’s house. The sympathetic prince gave him some money which he used to buy books and a glass-grinding machine. He rose to become manager of a glass factory in Munich and developed a new method of melting glass that enabled the production of high precision optical equipment. While measuring the refractive indices of different glasses, he noticed the dark lines in a sodium flame. He proceeded to measure the positions of hundreds of other absorption lines in the spectra of the elements.
Max Karl Ernst Ludwig Planck (1858-1947), a son of a professor of law at the University of Kiel,received his doctorate at the age of twenty-one and had a distinguished academic career that made him one of the leaders of science in Germany until his retirement in 1928. In 1900 he "guessed" the correct form for the blackbody radiation function and attempted to justify the formula by assuming that radiation consists of quanta of energy. Using the formula, Planck was able to deduce the value of h, the Boltzmann constant k, Avogadro’s number, and the charge of the electron; he received the Nobel Prize in 1918. Plank, whose career was marked by its devotion to the highest ideals, died broken by a series of personal tragedies: his elder son was killed in World War I, his daughters both died in childbirth in the next decade, and his second son was implicated in the plot against Hitler and executed horribly by the Gestapo in 1945.
Albert Einstein (1879 - 1955) published his theory of the photoelectric effect in 1905, the same year in which he published the Special Theory of Relativity and the paper on molecular dimensions which earned him his PhD from the University of Zurich. However, his reintroduction of the idea of a corpuscular nature for light met with considerable scientific resistance. Even Planck rejected an idea which seemed to set science back one hundred years. As late as 1913, when Einstein was proposed for membership in the Prussian Academy of Science, the nominating committee felt it necessary to apologize for this "mistake" as a singular error in a series of successes. Then, in 1921 Einstein won the Nobel Prize for the theory of the photoelectric effect. (Relativity was still controversial and was not mentioned in the award.)
Niels Henrik David Bohr (1885 - 1962), son of a renowned professor of physiology, received his doctorate from the University of Copenhagen in 1911, worked under Rutherford in England, and then returned to Copenhagen as a professor. In 1920, the Niels Bohr Institute was founded (by the Carlsberg Brewing Company) and became probably the most important center for physics in the world until the Nazi conquest in 1940. In 1943, Bohr, who was half-Jewish and outspokenly anti-Nazi, fled to England in the belly of a British Mosquito bomber and then came to the United States where he participated in the Manhattan project. Bohr was among the most admired of the 20th century physicists, not only for his great intellect and notable scientific achievements (he received the Nobel Prize in 1922), but also because of his kindly nature and devotion to humanitarian issues. He was one of the seven distinguished scientists in the Manhattan project who wrote asking that the atomic bomb not be dropped on Japan.
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