Gabriel Lippman (1845-1921) In 1886 the French scientist Gabriel Lippman invented a fascinating photographic technique, based on the phenomenon of light interference: recording color photographs in a black-and-white photographic emulsion. However, the practical execution of the technique appeared extremely difficult. In 1891, after years of patient experiments, Lippmann presented his invention to the Academy of Sciences. In 1894 he published his complete theory [1] and in 1908 his invention gained him the Nobel Prize for Physics. In this same year Herbert Ives published an excellent paper on Lippmann’s lucid invention [2]. The principle of Lippmann photography is presented in the next slide. It involves imaging a colored object, such as a rose, illuminated by white light, on an extremely fine-grained black-and-white photographic emulsion, placed in contact with liquid mercury that serves as a mirror. The red light of the rose is projected in the emulsion and is subsequently reflected by the mercury mirror. Incoming and reflected light now interfere to form an interference pattern of planes, more or less parallel to the emulsion. Lippmann, G., “Sur la théorie de la photographie des couleurs simples et composeés par la methode interferentielle,” J. Phys. (Paris), vol. 3, no. 97, 1894. 2. Ives, H.E., “An Experimental Study of the Lippmann Color Photograph,” Astrophysical J., Vol. 27, 1908, pp. 325-352.

n 2 l object photographic glass plate mercury mirror photographic emulsion lens green red n 2 l Principle of Lippmann color photography

Mirror Recording different wavelengths of light in Lippmann photography on an ultra fine-grained photographic emulsion by reflection from a high quality mirror in contact with the emulsion (schematic detail, greatly enlarged). See 5th Exhibition of Šechtl a Voseček Museum of Photography on-line

Microphotograph of a cross-section through a Lippmann photograph.

Microphotograph of a cross-section through a Lippmann photograph Microphotograph of a cross-section through a Lippmann photograph. A mirror was placed in contact with the emulsion at the right. Narrow bandwidth (3 nm) light of 633 nm wavelength impinged from the left and, on reflection from the mirror, created standing waves. (Courtesy of: Jean-Marc Fournier, The Rowland Institute for Science, Cambridge, MA.) (Reprinted with permission of IS&T, The Society for Imaging Science and Technology, sole copyright owners of The 10th Color Imaging Conference Proceedings.)

Color photographs made by Lippmann in the 1890s on ultra fine-grained silver halogenide emulsions.

Applications to document security? It is hardly imaginable that in the late 1800s such an advanced photographic technique was already conceived and realized. The resemblance with volume holography, published in 1962 by Yuri Denisyuk, is striking. Lippmann photography actually is the ancestor of volume reflection holography or Denisyuk holography, which is sometimes also referred to as Lippmann-Bragg holography. In the 2nd edition of Optical Document Security, in his unsurpassed chapter on thin film security devices, Dobrowolski writes on Lippmann photography: “Lippmann photography is an obsolete and very difficult method for making color photographs. [...] The physical and chemical properties of classical Lippmann emulsions rule out their use in document protection. However, modern volume holographic reflection structures, which are based on the same physical principles, may be constructed out of the more stable photopolymers.”

Applications to document security? And indeed, Hans Bjelkhagen in 1999, revives Lippmann’s technique and proposes its application in the field of document security, using DuPont’s panchromatic holographic photopolymer film [3-6]. Bjelkhagen shows that a reduced size Lippmann photograph can be made of a secure document, such as an identity card, credit card or travel document. This optically variable photograph can subsequently be laminated to the original document, to serve as a device that thwarts forgery as well as counterfeiting. This is illustrated in the next slide. Bjelkhagen also demonstrates that good quality Lippmann photographs can be made without the use of a mercury contact mirror, because the reflection at the film-air interface suffices for producing efficient Lippmann photographs. Bjelkhagen, H.I., “New Optical Security Device based on One-Hundred-Year-Old Photographic Technique,” Opt. Eng., Vol. 38, 1999, pp 55-61. Bjelkhagen, H.I., “A New OVD based on Interferential Photography recorded in Holographic Materials,” SPIE Proceedings, Vol. 3638, 1999, pp. 87-95. Bjelkhagen, H.I., “The Lippmann OVD for Enhanced Document Security,” Proceedings of the Conference on Optical Security and Counterfeit Deterrence Techniques III, 27-28 January 2000, San José, CA, vol. 3973, pp. 257-265. Bjelkhagen, H.I., “Secure Photographic Method and Apparatus,” Photics Corp (USA), patent no. US 5,972,546, filed January 22, 1998, published October 26, 1999.

Sample passport with Lippmann photograph in the upper right corner, under normal observation (left) and under an angle (right) showing the Lippmann photograph in negative contrast. The photo’s on the bottom show the Lippmann photograph in detail. (Courtesy of: Hans Bjelkhagen, De Montfort University, U.K.) Also see http://www.holographyforum.org/HoloWiki/index.php/Lippmann_Security