Nicholas J. Phillips

Micro-optic studies using photopolymers

This paper addresses a set of problems accessible via the technology of photopolymers. Though most interest in micro-optic fabrication centers around the older technology of melted photoresist and the much newer area of binary optics, much can be learned from the area of photopolymers of the graded index type. Recent advances in the technology of the DuPont materials for example, make possible the fabrication of novel micro-optic systems. We examine the manufacture of micro-lens arrays using contact and other forms of lithography. The relative merits of simple refractive optics and graded index optics are discussed. This work has been applied to the formation of specialized diffusion screens for image projection and the advantages are pointed out in the discussion.

Edge-illuminated holograms, evanescent waves, and related optical phenomena

Revised interest in edge-illuminated holograms has resulted in new studies of optical phenomena which are not widely appreciated. The formation of edge-illuminated holograms requires a study of uncommon optical regimes and yields results which are not in keeping with common expectation. In this paper, we take another look at the edge-illumination problem but uncover some historically interesting work in the area of evanescent waves that provides us with unexpected new insights.

Chemical symmetry: developers that look like bleach agents for holography

The holographic scientist has a long experience of developing and bleaching methods for the silver halides. There is however an underlying asymmetry of the chemical armoury. Whilst numerous developers have evolved throughout the history of photography, there is a paucity of organic bleach compounds that mimic their developing counterparts. This paper discusses the synthesis of novel bleaches starting with a range of developing agents. The door is opened to relatively safe long-keeping organic bleach agents with improved toxic hazard levels.

Dichromated gelatin--some heretical comments

This paper looks at some ideas old and new that relate to the formation of images in dichromated gelatin. The traditional view that the dichromated system hardens gelatin thus preventing solubilization of the material must be balanced against other observations such as that of the reduction of the bulk index of the gelatin layer and the appearance of gelatin in the processing solutions. We revisit the problem and take a look at some new chemical ideas that relate to the behavior of gelatin during bleaching of silver halides. A new method for the processing of silver halide-sensitized gelatin (S.H.S.G.) is proposed which endows the silver halide emulsion with more than three orders of magnitude of speed when compared with D.C.G. per se.

Bridging the gap between Soviet and Western holography

The history of Soviet holography is dominated by the invention of the reflecting hologram by Yuri Dcnisyuk, the development of ultra-fine grain recording materials by the work of Kirillov and the evolution of colloidal processing techniques under Usanov. The colloidal images so created are of very low noise and high definition and were a shock to Western scientists at the Holography meeting in Ulyanovsk in 1979. The general approach to making silver halide reflection holograms in the West is to use staining pyrogallol developers and bleaches which involve physical transfer of halide to create the modulation. This paper deals with a previously unpublished process for the silver halides created by the author in 1979 which bridges the gap between the Soviet and Western methods.

Holograms in the edge-illumination geometry: new materials development

Some rigorous statements are made about the recording of holograms in the true edge- illuminated geometry. An essential asymmetry is outlined between the role of the substrate refractive index and that of the recording medium. Laboratory observations indicate that unique possibilities exist for recording in this regime using the photopolymers of Du Pont. Unlike any other regime of holography, numerous optical criteria have to be met simultaneously. We believe that self-induced index matching between the recording polymer layer and the substrate on which it is mounted is the key to a workable recording system.

Colour Reflection Holography

This paper discusses some of the current knowledge of modulation mechanisms and how they affect the recording of colour reflection holograms in particular and all holograms in general. Recent observations have revealed spurious complexing problems during bleaching of silver halide holograms and these will be discussed in relation to their effect on hologram efficiency.

Experimental techniques for the evaluation of light-induced microlens formation in photopolymers

This paper discusses the formation of GRIN lenses by optical exposure of photopolymer (Du Pont) and the setting up of a simplistic test experiment for evaluation of resulting polymer optical elements. An essential aspect of the work relates to the duration of the exposure. We address the question of differences of performance related to whether the exposure time is greater than or less than the characteristic time scale of monomer diffusion.

New developments in sol-gel imaging

This paper addresses the properties of sol-gel silica in relation to its potential to provide new devices for optical imaging. Although the sol-gel method opens the door to unprecedented levels of purity of silica materials, it is also beset with problems of the achievement of extreme optical homogeneity. The work reported discusses experiences with sol-gel silica intra cavity elements in ion lasers and new concepts of imaging and laser structures based on fabrication via porous gel-silica. A new physical model for etalons is proposed which shows advantages of porous gel-silica over conventional fully dense materials.

Sol-gel technology

The paper will discuss some of the technology of sol-gel manufacture and will touch on such subtle problems as porosity of sol-gel prepared silica layers.