Gabriel Lippman

Jonas Ferdinand Gabriel Lippmann (Bonnevoie, Luxembourg, August 16, 1845 – July 13, 1921) was a French-born Luxembourgish physicist who was awarded the Nobel Prize in Physics in 1908 for his method of reproduction of colors in photography, based on the phenomenon of interference. His discovery allows the complete reconstruction of all the wavelengths reflected by an object.

Biography

Coming from a French family, Gabriel Lippmann was born in Luxembourg. He studied in Paris, at the Henri IV Lyceum and from 1868 at the Ecole Normale Supérieure. Despite being a brilliant student, he was not a lover of discipline. He suspends the oppositions to the institute chairs. His academic career was not especially brilliant, since he only concentrated on those subjects that interested him, belittling the others. He travels to Germany to participate in an official scientific mission, which allows him to work with Wilhelm Kühne and Gustav Kirchhoff in Heidelberg and with Hermann Ludwig von Helmholtz in Berlin.

Lippmann returns to Paris at the beginning of 1875, and begins to work first in his own home and later at the Sorbonne. He defended his doctoral thesis in Sciences on July 24, 1875. He then joined Jules Jamin's Laboratory of Physical Research, linked to the Escuela Práctica de Altos Estudios, until his appointment as professor at the Paris Faculty of Sciences in 1878.

Professor Lippmann at the Sorbonne Physics Laboratory (Sorbonne Library, NuBIS)

In 1883, he was appointed professor of mathematical physics at the Sorbonne, succeeding Charles Briot, and in 1886 professor of general physics, succeeding Jules Jamin, and his replacement in the chair of mathematics would be Henri Poincare. That same year, he is elected to the Academy of Sciences, replacing Paul Desains (Lippmann obtains 31 votes, against 20 for Henri Becquerel), Academy of which he will be president in 1912. He also becomes director of the Physical Research Laboratory.

He was honorary president of the French Society of Photography between 1897 and 1899, succeeding Étienne-Jules Marey, and participated in the creation of the Institute of Theoretical and Applied Optics.

Lippmann worked in many fields, including electricity, thermodynamics, optics, and photochemistry. In Heidelberg, he studied the relationship between electrical and capillary phenomena. Precisely on this subject he elaborated his doctoral thesis ( Relations between electrical and capillary phenomena ). These investigations were the necessary basis for the construction of a precision instrument called capillary electrometer, which was used in the first electrocardiographs and the coelostat, an instrument that compensates for the rotation of the Earth and allows a region of the sky to be photographed, leaving it apparently fixed.

He invented the Lippmann color photography procedure, which until 2005 was still the only one that could fix all the colors of the spectrum instead of carrying out a trichromatic decomposition (which is, moreover, irreversible). The procedure, which fixes the light interference fringes, is expensive (as it requires the use of mercury) and requires a long exposure time, but in terms of quality it has not yet been surpassed today (2006). It is also especially interesting since it is the only one that allows a complete chromatographic analysis a posteriori of the fixed colors, which is by nature impossible with trichrome procedures. The Lippmann procedure served as the basis for the discovery of holograms.

Lippmann died at sea on July 13, 1921, while returning from a visit to the United States.

Interferometric photography

Color photography by Gabriel Lippmann

Professor Lippmann had developed the general theory of his procedure for the photographic reproduction of colors in 1886, but it was not submitted to the Academy of Sciences until February 2, 1891. The procedure is based on an interference method. In 1893 he was able to present to the academy photographs taken by the Lumière brothers in which colors were reproduced with excellent orthochromatism. He published his theory in full in 1894. To fix the colors, he used a glass plate coated with a photosensitive emulsion based on silver nitrate and potassium bromide. The light then enters the machine and follows two different paths to hit the plate and cause the silver particles to react.

This procedure must not be confused with the Autochrome of the Lumière brothers themselves, better known, and which has left color images from the end of the century XIX. This procedure worked with pigments, unlike Lippmann's method. This discovery earned him the Nobel Prize in Physics in 1908.

Basics

A stationary wave. The red dots are the nodes of the wave

In optics, the phenomenon of interference occurs as a result of the propagation of light waves. When light of a certain wavelength is reflected back on itself by a mirror, standing waves are generated, in the same way that waves resulting from a stone thrown into still water create standing waves when reflected from a surface such as a stone wall. a pool. In the case of ordinary light, which is incoherent in nature, standing waves are distinguishable only within a microscopically thin volume of space adjacent to the reflecting surface.

Lippmann made use of this phenomenon by projecting an image onto a special photographic plate, capable of recording details smaller than the wavelength of visible light. The light was passed through the glass plate supporting a very fine and almost transparent photographic emulsion containing submicroscopically small grains of silver halide. A time mirror of liquid mercury in intimate contact reflected light back through the emulsion, creating standing waves whose nodes produce minimal effect, while their antinodes create a latent image. Once the plate was processed, the result was a laminar structure, with different parallel layers composed of submicroscopic metallic silver grains, which formed a permanent record of the standing waves. In each part of the image, the spacing of the slices corresponded to the half-wavelengths of the photographed light.

The finished plate is illuminated from the front at a nearly perpendicular angle, using natural light or another white light source that contained the full range of wavelengths in the visible spectrum. At each point on the plate, light of approximately the same wavelength as the light that had generated the sheets was strongly reflected back at the observer. Light of other wavelengths that were not absorbed or scattered by the silver grains simply passed through the emulsion, to be absorbed by a black antireflective coating applied to the back of the plate after it was fixed. The wavelengths, and therefore the colors, of the light that had formed the original image are reconstituted, giving a full color image.

In practice, Lippmann's process was not easy to use. Extremely thin layered, high-resolution photographic emulsions are inherently much less sensitive to light than ordinary emulsions, so long exposure times are required. With a large aperture lens and a brightly sunlit subject, a camera exposure of less than a minute was sometimes possible, but exposures measured over several minutes were common. Pure spectral colors were reproduced brilliantly, but broad, ill-defined bands of wavelengths reflected from real-world objects could be problematic. The process produced no color prints on paper, and it proved impossible to make a good duplicate of a Lippmann color photograph by re-photographing it, so each image was unique. A very shallow angled prism used to be attached to the front of the finished plate to deflect unwanted surface reflections, and this made sizable plates impractical. Lighting and viewing arrangement required to see colors to best effect excluded normal use. Although special plates and a plate holder with a built-in mercury reservoir were commercially available for a few years around 1900. Even expert users were unable to obtain consistent results, and the process never became more than a scientifically scientific laboratory curiosity. elegant. However, it did stimulate interest in the development of color photography.

Lippmann's process foreshadowed laser holography, which is also based on recording standing waves on a photographic medium. Denisyuk reflection holograms, often referred to as Lippmann-Bragg holograms, have similar lamellar structures that preferentially reflect certain wavelengths. In the case of real multi-wavelength holograms of this type, the color information is recorded and reproduced exactly as in the Lippmann process, except that highly coherent laser light passing through the recording medium and reflecting from the subject generates standing waves in a relatively large volume of space, eliminating the need for reflection to occur immediately adjacent to the recording medium. Unlike Lippmann's color photography, however, the lasers, subject, and recording medium must be kept stable within a quarter of a wavelength during the exposure for standing waves to be properly recorded or not detected..

Eponymy

• The lunar crater Lippmann carries this name in his memory.