James J. Cowan

Holographic Honeycomb Microlens

A honeycomb close-packed microstructure can be recorded in a positive photoresist layer by a simultaneous exposure of three coherent laser beams. A close-packed square structure results from a simultaneous four-beam exposure. The structure consists of parabolic-shaped depressions in the surface. By replication and embossing techniques, it is possible to impress the mirror image of the microstructure into plastic, such that the top surface consists of parabolic-shaped posts, or microlenses. The size of each microlens can be varied from around one micrometer to a millimeter or more. There are wide-ranging applications for such regularly spaced and precise structures, extending from solar concentrators to three-dimensional imaging devices.

The Recording And Large Scale Replication Of Crossed Holographic Grating Arrays Using Multiple Beam Interferometry

In the photographic industry, two dimensional periodic arrays, or hole patterns, that have a periodicity on the order of one to several micrometers, can have many significant applications. One use of such an array is the regular positioning of photosensitive elements, including, for example, photographic emulsion grains, into film systems of exceptionally low noise. A method is described for producing the array patterns using the technique of multiple beam interferometry applied to the already well known techniques of holographic grating formation. In the first process a square hole pattern is formed using two sequential two beam interference exposures in a thick layer of positive photoresist. Upon development an array of hills and valleys is formed, with the valleys corresponding to the holes and occupying about half of the available surface area. In the second process a hexagonal close packed hole pattern (honeycomb array) is formed using a single simultaneous three-beam coherent exposure of the photoresist. In the third process a square close packed hole pattern (egg-crate array) is formed using a single simultaneous four-beam exposure. The second and third processes produce surface depressions in the photoresist layer that occupy practically all of the available surface area. Because the periodic arrays are required in large quantities, the patterns formed in photoresist must be replicated. A nickel master is made from the original photoresist by electroplating, and this master is then used to repeatedly emboss the pattern into long plastic sheets. A description is given of the special industrial requirements for making high quality embossed patterns in this way on a large scale.

The Holographic Honeycomb Microlens

A honeycomb close-packed microstructure can be recorded in a positive photoresist layer by a simultaneous exposure of three coherent laser beams. The structure consists of parabolic shaped depressions in the surface. By replication and embossing techniques, it is possible to impress the mirror image of the microstructure into plastic, such that the top surface consists of parabolic shaped posts, or microlenses. The size of each microlens can be varied from around one micrometer to a millimeter or more. There are wide-ranging applications for such regularly-spaced and precise structures, extending from solar concentrators to three-dimensional imaging devices.

Blazed Holographic Gratings-Formation By Surface Waves And Replication By Metal Electroforming

The formation of a blazed holographic grating, using the interference of an ordinary plane wave with a surface wave is considered. The usual holographic recording arrangement has been modified such that a positive photoresist recording layer is coated on one face of a prism; one of the recording beams is totally reflected from the prism such that the surface wave thus formed enters the photoresist from the back side. The other recording beam also enters from the back side, but is an ordinary plane wave. The resulting interference fringes are inclined with respect to the normal. With this arrangement the profile can be contoured more precisely than usual and many variations in the shape of the profile are possible. Modifications of the method described here allow the formation of gratings on curved surfaces and in some cases correction for aberrations. Once a profile has been formed in this fashion in photoresist it is possible to replicate it exactly in a durable metal layer using electroforming techniques. Such gratings are applicable for use in specrometers where high beam intensities must be taken into account.

Holographic Embossing at Polaroid: The Polaform Process

Embossing of replica holograms at the Polaroid Corporation is being done in two major areas: crossed grating arrays for development of new types of photographic films and holographic optical elements; and the production of white-light viewable display holograms of various types for many diverse applications.