Radiation imagery chemistry: process – composition – or product th – Holographic process – composition – or product
Reexamination Certificate
2000-05-24
2004-05-04
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Holographic process, composition, or product
C430S002000, C359S012000, C359S003000
Reexamination Certificate
active
06730442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the use of contact holography to form multiple holograms and, more particularly, to the use of contact holography and a master hologram to make replica gratings, lenses, switches and other images wherein one or both of the master hologram and corresponding replica comprise a polymer-dispersed liquid crystal (PDLC) material.
2. Description of the Related Art
Once a hologram has been recorded, whether using simple or complex optical geometries, it is often desired to reproduce or reconstruct the hologram so as to have multiple copies which are substantially identical to the originally recorded hologram. There are numerous methods for reconstructing holograms, however these are cumbersome and involve retracing the steps used to create the original or master hologram. Unfortunately, where complex geometries are involved, this is neither an efficient nor a practical method for performing mass reconstruction.
By way of example, U.S. Pat. No. 3,580,655 to Leith (“Leith”) which is incorporated herein by reference, sets forth multiple methods both for formation of the master hologram and for reconstruction of the master hologram, either for viewing or for permanent recording. While the subject matter of the current invention is not centered on the formation of the master hologram, the advantages of the current invention are readily apparent when the complexity of this initial formation is recognized. For example,
FIG. 1
(
FIG. 7
of Leith) illustrates one of the simplest geometries for forming a master hologram. This simple configuration illustrates the basic components for simple holographic construction, including a coherent light source
10
emitting an incident beam
12
. From this incident beam
12
, two separate beams are formed. A prism
14
or similar light-splitting or directing device intercepts part of the incident beam
12
and directs a reference beam
16
to a detector plate
18
. Simultaneously, a part of the incident beam is diffused by a diffusion screen
20
and diffracts off an object
22
, forming an object beam
24
, which also passes onto the detector plate
18
. The interaction between the reference beam
16
and the object beam
24
produces an off-axis hologram, in the form of multiple Fresnel patterns and interference fringes.
Further in Leith, there is a method and system for using the master hologram from
FIG. 1
to produce replicas of the master hologram.
FIG. 2
a
represents the simplest system and method for duplicating the master hologram. Referring to prior art
FIG. 2
a
, there is an incident beam
12
from a coherent light source
10
which forms two separate beams, a reference beam
16
and an object beam
24
. In this case, object beam
24
results from the interaction of part of incident beam
12
with the master hologram
26
. Due to the grating effect of the master hologram
26
, the object beam is directed along the formation angle and a detector
18
is placed at the intersection of the reference beam
16
and the object beam
24
, forming a replica of the interference pattern comprising master hologram
26
. In this case, the object beam forms a virtual image of master hologram
26
which is recorded on the detector
18
. The real image is not used in the reproduction process.
As is clear to one skilled in the art, this method of master hologram duplication, while viable, results in a number of disadvantages. In any situation involving light traveling through an optical train, there is the potential for misalignment of the optical elements. Further there are inherent efficiency limits for each optical element. These disadvantages can result in unwanted diffraction, reflection, and in some cases aberration of the beams. Additionally, while lasers have improved coherence parameters, coherence length remains an issue. Even the simplest dual beam recording and duplication systems described above require precise alignment for optimal results. The conventional systems above also require multiple optical elements even for the simplest holographic formation geometries. Consequently, complex geometry hologram formation is not available with the Leith system because of the length and requisite multiple components of the optical train.
The prior art also contemplates a single beam master hologram duplication system that greatly reduces the number of necessary optical components. Referred to as contact printing, this system for duplicating a master hologram resembles in many respects the art of photography. The master hologram and a holographic detection plate (e.g., emulsion plate) are placed in optical contact with one another and exposed to light. Photographic development of the holographic detection plate results in a replica master hologram. For a fully successful reproduction, the optical contact between the master hologram and the holographic detection plate must be such that there is no loss of resolution within the interference fringes. Establishing the requisite optical contact has proved to be a significant limiting factor in attempts to use contact printing for duplication of holograms. Consequently, the prior art single-beam contact printing method, though it reduces the number of optical elements necessary for duplication of a master hologram, poses new optical hurdles to the art of hologram replication.
Referring to
FIG. 2
b
, a prior art single beam contact printing system is illustrated in accordance with U.S. Pat. No. 5,547,786 to Brandstetter, et al. (“Brandstetter”), the specification of which is incorporated herein by reference. The system of Brandstetter includes a source of monochromatic, collimated light of substantially fixed wavelength such as laser
10
which produces an output beam
12
, referred to as the replication or recording beam, and directs that beam through beam conditioning means
80
, which preferably comprises lenses
82
and
84
, pinhole
86
, and filter
88
. Lenses
82
and
84
and pinhole
86
are provided to collimate beam
12
and to expand that beam to the desired size filter
88
is provided to control or adjust the intensity or amplitude of beam
12
across its profile as desired. Subsequent to conditioning by means
80
, the conditioned beam
12
is directed at a desired angle onto master holographic optical element
26
, passes through, and directly enters a phase recording medium
18
, such as a photopolymer layer that has been applied onto the backside of the master holographic optical element.
The method for forming the replica within the photopolymer layer requires a polymerization step which is separate from the recording step. Further, the resulting replica hologram is not switchable. Further, the recording mediums currently available as blanks for hologram duplication are limited in their ability to provide optimal optical contact with the master hologram.
Accordingly, there remains a need for a system and method for mass reproduction of holograms, having a single beam contact printing method using an optically superior recording medium.
In conventional contact holography methods and systems, situations exist wherein the use of a static, as opposed to a switchable, master hologram is limiting. First, a static hologram is limited to a single diffraction efficiency, which is always ON (i.e., it cannot be turned OFF). Second, even though a non-recording wavelength theoretically should pass through the static hologram without causing recording in the blank, in practice this is not the case. Instead, a non-recording, incoherent wavelength passing through a static master may result in unwanted scattering and cross-coupling of phase information which can decrease diffraction efficiency, introduce cross-gratings, increase haze, and generally decrease the signal-to-noise properties of the replicated grating. These limitations of the static master hologram result in difficulties with contact recording schemes that require either in situ pre-recording or post-recording irradiation of the blank.
Accordingly, a need remains
Brandelik Donna M.
Pogue Robert T.
Sappington John
Shepherd Christina K.
Siwecki Stephen A.
Angebranndt Martin
Kilpatrick & Stockton LLP
Science Applications International Corporation
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