Optically Developed Free-Radical Photosensitive Materials

Abstract

Free-radical photosensitive materials are based on a photoinitiated reaction between an aromatic amine and a halo-methane. The formation of an organic dye is a consequence of this reaction. At low exposure levels, trace quantities of dye are formed which optically sensitize the free-radical material to longer wavelengths. Thus, a faint or latent image may be optically developed by uniformly irradiating the film with illumination whose wavelengths lie within the absorption spectrum of the latent image dye and outside of the initial spectral sensitivity region of the film. In this manner it is possible to intensify the initial latent image by a factor of 100 to 1,000 with a corresponding increase in photographic speed. A wide variety of free-radical photosystems have been prepared having sensitivities in different proportions of the spectrum, differing image colours, and varying sensitometric properties. A typical system is described and the nature and limitations of optical development discussed. A possible mechanism for optical development is proposed.

Notes

Paper presented at a Symposium on “Non-Silver Photographic Processes” organized by the Science Committee of the Royal Photographic Society on 30 September to 3 October 1969, at Oxford.