Perot
NAME: Perot, Alfred.
ACHIEVEMENT(S): Collaborated with Charles Fabry on the Fabry-Perot interferometer.
NICKNAME/ALIAS: full name, Jean-Baptiste Gaspard Gustav Alfred Perot.
DATE/PLACE OF BIRTH: 3rd November 1863, in Metz, France.
DATE/PLACE/AGE AT DEATH: 28th November 1925, in Paris, France. Aged 62.
DISCIPLINE: Physicist.
FIELD: Physics.
LANGUAGE: French.
PARENTS: ?
SIBLINGS: ?
SPOUSE: ?
CHILDREN: ?
EDUCATION: Ecole Polytechnique, 1880-84; University of Nancy, 1884-88.
MAJOR WORK: "Sur une Nouvelle Methode de Spectroscopie Interferentielle"
("On a New Method of Interference Spectroscopy"), with Charles Fabry, 1898.
LIFE AND TIMES: Perot was awarded his doctorate in 1888 for measurements of the specific volumes of saturated vapors, and for determining the mechanical equivalent of heat using a method based on the equations of the civil engineer <used method of> Clapeyron*.
In the same year, he took a teaching and research post at the University of Marseilles and began to study electricity. Over the next few years he studied dielectric properties and electromagnetic waves, and soon became known in the emerging electrical industry.
In 1894, his reputation won him a special chair in industrial electricity, created for him at Marseilles University and a year later he wrote an influential paper, "Les Applications Industrielles d'Electricite".
Around this time, Perot began collaborating with fellow-physicist <collaborated with> Fabry*, to develop a new method of optical interferometry. Fabry was trying to measure the distance between metallic surfaces about a micron apart. He used interference between rays of light that had undergone different numbers of reflections between the two surfaces to be measured.
This work prompted Fabry and Perot to study the very fine fringes produced by reflections between silvered films, which led to the development of the Fabry-Perot interferometer. According to Fabry, he and Perot worked well together, Fabry contributing the theoretical work and Perot concentrating on design and construction of the mechanics.
The interferometer is an instrument for making precise measurements using beams of light. It works by dividing light into a number of beams that travel unequal paths, whose different intensities interfere with each other and appear as a pattern of light and dark bands, known as interference fringes.
The "variable-gap" interferometer of Perot and Fabry, developed in 1896 and produced the following year, consisted of highly reflective parallel mirrors on two planes (known as an etalon). These, because of their high reflectivity, gave successive multiple reflections of light waves, which gradually diminished in intensity and formed very narrow, sharp fringes. These fringes were then measured and used to reveal hyperfine structures in line spectra and to evaluate the widths of narrow spectral lines.
The Fabry-Perot interferometer, although not the first of its kind, was notable because it produced sharper fringes than the instrument developed by the American physicist Albert Michelson in 1881. Until 1901, Fabry and Perot applied their instrument to spectroscopy and metrology, during which time they established a series of standard wavelengths.
In 1898, Fabry, Perot and Mace de Lepinay, who had already used optical methods of measurement in 1885, used the new interferometer to calculate the mass of a cubic centimetre of water.
Over the next three years, Fabry and Perot then used their silvered film interferometer for spectroscopic analysis and measured the wavelengths of the black lines in the solar spectrum.
After 1901, Perot continued his work on solar spectra and spent many years analysing the small shifts in wavelength produced by a variety of effects, including pressure, convection currents and the Doppler Effect due to rotation.
This work involved separating some of these effects and, from 1920 to 1921, he tried to verify the gravitational red shift of Einstein's general theory of relativity. This experimental verification of the gravitational red shift proved extremely difficult. Perot died before finishing his work and conclusive measurements were not made until 1960.
ASSESSMENT: Ingenious with apparatus and, as a teacher, preached the importance of experimentation.
EXTRA CONNECTIONS: His work was later used by <work later used by> Townes*
ONELINER: Alfred Perot co-inventor of the interferometer
BIBLIOGRAPHY:
DSB.