Note: Descriptions are shown in the official language in which they were submitted.
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The present inven-tion relates to an apparatus for the
viewing of holograms. A particular application is an apparatus
for the viewing of holograms in non-coherent light.
This application is a divisional application of copend-
ing application ~o. 421,426 filed February 11, 1983.
A proposal for whi-te light display of a hologram is to
be found in an article "Display of Holograms in White Light'l,
C.s. surckhardt~ seil Systems Technical Journal, December 1966,
pages 1~41-4. A hologram is illuminated from behind. In front
of the hologram is ~ venetian blind and a plane grating whose
pitch corresponds to an interference pattern formed by li~ht
beams at the same a~gle as the mean angle be-tween the subject
beam and the reference beam used in making the hologram. rI'hus,
the average fringe spacial frequency of the hologram is equal to
that of the grating. The slats of the venetian blind are at such
an angle that they block direct light but allow through the first
order diffracted light. This will be subject to severe colour
dispersion but the second diffraction by the plane grating com-
pensates for this so that the viewer sees a monochrome three-
dimensional image behind the hologram, provided that the viewing
and illuminating angles are correct.
In spite of this proposal in 1966 and increasing inter-
est in holograms practical white light holograms displaying full
parallex have not become readily available. Nor has it been pos-
sible to provide sirnple, direct viewing multi-colour holograms.
This invention is predicated upon a particular set o~
components which may be grouped according to a number of permuta-
tions each of which has a specific application. The disadvan-
tages and lirnitations encountered in the prior art can be miti-
gated and new and useful devices producedO
According to a first aspect of the present invention as
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disclosed and claimed in copending application No. ~21, 426, there
is provided a hologram viewing apparatus comprising a
- la -
housing, a ligl-lt source and a screen, the housing ha~ing a wall
and erlclosing lhe liyht source whicll illuminates l:he screen, -the
screen be:ing located with the said wa]l of the housirlg and
consisting of at least a plane gratlny, there being hologram
holdin~ means associated W ith the housing for holdlng a hologram
adjacen-t the screerl for viewing of the hologram. Suitably the
screen comprises fllterLng means for the reconstr-lct10rl of
multicolour surface relief holograms.
~ccording the a second aspect of the present invention
-there is provided an integral direct viewing hologralll device
comprisillg a venetiarl blind film having a holograln enlhossed on or
bonded onto one surface and a plane grating embossed on or bonded
onto the other surface. Suitably -the device further comprises
filtering means for -the reconstructlon of multicolour surface
relief hologram.
~ ccording to a third aspect of the present invention
there is provlded an article useful in -the manufacture of
hologram devices, comprising a venetian blind film embossed or
bonded on one side wi-th a plane grating. Suitably tlle article
fur-ther comprises filtering means for the reconstruction of
multicolour surface relief holograms.
The viewing apparatus provides a particularly simple
and self-conta;ned unit the screen of which com~rises at least
one o~ the componen-ts necessary -to form -the direct viewlng
holoyram ~evice of the inventior.~ The hologram devices
themselves when intended for use with the viewing appara-
tus can be formed without the component or components
provided by the screen of the the viewing apparatus. The
5 cost of manufacturing the holograms can therefore be
significantly reduced ~hile the cost of including the
plane ~rating does not signific~ntly affect the cost oE
the viewing apparatus. It is also possible to include the
venetian blind film as a part o the viewir~g apparatus
10 thus enhancing the advantageous appropriation of cost
between viewing apparatus and hologram devices.
The hologram device of the invention is an integral struc-
ture which can be handled freel~ and which can be manufac-
tured cheaply, particularly in large numbers.
15 The direct viewing hologram device of this invention
differs from the proposal of 1966 by the provision of a
venetian blin~ film in place of the mechanical slats and
by the fact that the hologram device of this invelltion is
an integral structure. A major point of distinction
20 between the hologram device of this inventlon and the
previous proposal is the embossing or bonding of the holo-
gram onto a venetian blind film. Provision of the plane
grating by embossing or bonding onto the venetian blind
film further enhances the distinctive nature and utility
25 of the hologram device of this invention.
Venetian blind film is available as "light control film~
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froTrl Minnesota Mining and Manufdcturing Company with
opaque ~slats" or "lo-lvres" in the Eilrn its~l~ at a pitch
of approximate-y 10 peL millimetre and at various slat
angles. A convenient angle for the purpose of this inven-
tion is 45 and a convenient view angle, as specified bytt,e manufacturers, is 6n.
In generai i~ is possible to use either thin film or thick
film holograms, the former being provided by embossing and
the latter being provided, for example, photographically
with subseq~ent bonding of that photographic film to the
venetian blincl film. The plane grating may also be
embossed or, if, for example, it is in the form of a
photographic film, bonded onto the venetian blind filTn.
The venetian blind film embossed OTI one side with a plain
grating can be combined with holograms so as to form
direct viewiny hologram devices.
In order to provide multi-coloured ima~es, the invention
further provides a hologram device wherein there are two
or more holograms made in different coloured light and
provided on the said one surface of the venetian blind
film. In this development of the invention it is prefer-
able to use thick film holograms because of their selec-
tivity to the colour of light in which they were made. In
general, saturation increases with hologram thickness. On
the other hand the grating is preferably thin.
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In this invention, it is preferred to utilize imaye plane
holograms because of their greater image sharpness. Two-
step or lens techrliques for forming image plane hologramsare well known.
5 Embodiments of the invention will now be described by W?~y
of example only and ~ith reEerence to the accompanying
drawings, in WhiCil:
Figure 1 shows a hologram device embodying one aspect
of the invention, and
Figure 2 shows a hologram viewing apparatus in sketch-
matic section.
Referring to Figure 1, a venetian blind film 10 has two
thick holograms 11 and 12 bonded in face-to-face relation-
ship with each other and bondecl onto one surEace of the
15 film 10. A plane grating 13 is bonded or embossed on the
other side of the venetian blind film 10. The holograms
11 and 12 are made in different coloured light, for
example blue and red respectively, and with different mean
angles between object and reference beams such tllat the
20 average fringe spacial frequencies of the holograms are
all equal and equal to that of the grating. The device
can be viewed from either side, the image remaining ortho-
scopic. For a monochrome image, the film 12 can be
omitted and the hologram film 11 can be made in any colour
25 coherent li.ght. The film 11 can be replaced by a hologram
embossed on the surface of the venetian blind film 10.
Methods for forming embossed ho1oc3rams are knownO A
method of forl-ning an embossed hologram suitable for
producing a multi-colour image may comprise the following
steps:
forming an interference fringe pattern in a first
group of areas on a photographic medium using a first
coherent liyht source,
producing a further interference fringe pattern on a
second group of areas on the photographic mediurn,
displaced ~rom and distinct from the first grollp of areas,
using a coherent light source of different wavelength from
the first,
processing the photographic medium so that the fri.nge
patterns are recorded as regions of varying optical
15 density,
- providing a positive photoresist layer on the
processed photographic medium,
exposing the combination so as to provide a latent
irnage of the ~ri.nye patterns in the photorecist layer and
processing the photoresist layer so as to provide a
surface relief hologram.
When using this rnethod it is believed that optimum results
are obtained by selecting the reference angle between the
object and reference beams for each liyht source so as to
25 ensure t~la~ the average spatial frequency of each o~ the
fringe patterns is equal to the spatial frequency of the
plane grating with which the hologram is to be associated.
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A multi-colour image may be reconstructed from such a
hologram using white light which passes through a multi-
colour mask the mask being in registration with the holo-
gram such that a given colour in the rnask is adjacent the
5portions of the hologram corresponding to that colour.
If differen~ reference angles are selected as describe~
then dispersed white light should be used to reconstruct
- the final image. ~ithout the use oE different reference
angles for each li-~ht source the separate colour irnages
lOtend not to register with each other thus degrading the
multicolour reconstructed image. Dispersed white light is
provided by the plane grating of the viewing device.
In the above description the n~l;nber of coherent light
sources, and corresponding groups of areas, can be greater
15than two if appropriate.
A surface relief hologram of this forrn can be used to form
a master which rnay be pressed into the surface of poly-
meric sheets so as to provide inexpensive replicas of the
holograms.
20Fiyure 2 illustrates an apparatus for use in viewiny holo-
grams. The apparatus comprises an opaque housing 20
enclosing a lamp 21 which may be in the forrn of a quartz-
halogen lamp fed by a power supply unit 22. Light from
the lamp 21 is collimated into a beam 23 by an optical
25 systern inclu~ing lenses 24, a diaphraym 25 and a concave
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mirror 2~. The lighL beam 23 illurninates the back of the
viewin~ screen ~hich is provided in a wall of the
housing. The screen consists of at least a plane diffrac-
tion grating 28 but preferably also includes a venetian
S blind film 27, as shown. The diffraction grating 28 is
placed against, bonded or embossed on the rear surface of
~he vene~ian blind film 27.
It wi11 be appreciated that the viewing apparatus of
figure 2 provides the plane grating and venetian blind
10 film required by the above described hologram device.
Consequently, when intended for use with the viewing
apparatus of figure 2 the holograrn devices need only
comprise an embossed or thick film hologram. The manufac-
turing cost of each holograrn device is therefore slgnifi-
15 cantly reduced while the manufacturing cost of includingthe dirfraction grating and venetian blind film in the
viewing apparatus is relatively insignificant.
In the absence ~f a hologram, tlle screen appears dark. A
hologram 29 can be placed over the screen, clips or guides
20 being provided for holding the hologram in place.
Provided that the hologram is appropriately made to match
the gratiny, an image appears and may be viewed.
With the use of a light source having an exceptionally
25 fine filament, parts of the optical system within the
housing 20 may be dispensed with. It is conceivable that
some applicatiolls may benefit from a slightly convergent
rather than collimated illuminatiny beam.
In order to enable the image to be examined in detail, a
magni~ier 30 rnay be mounted on a linkage 31 which allows
the magnifier to be moved freely to any screen position
while maintalning an orientation such that the total
dispersion is minimized.
The viewing apparatus is considered to be particularly
beneficial for its practical utility and can be adapted
for specific applications. One such application is to
emulate a microscope and this application presents commer-
cial advantages for use as an educational, researcn or
other aid.
The housing oE the viewing apparatus is formed so as to
have an external conEiguration similar to that of a
conventional microscope. The holograms to be used with
this viewing apparatus aLe prepared with e~posure to
illumination from the objective lens of a microscope which
is focused on the required sample. In the viewing appara-
tus the reconstructed holographic image simulates the
intermediate microscope irnage. The viewing apparatus
includes an appropriate conventional eyepiece and conse-
quently the final image seen by the viewing apparatus very
closely resembles that seen by using a conventional micro-
scope. The apparatus will func.ion in a similar manner to
a conven~ional microscope with the microscope slide
replaced with a hologram. This is particularly advan-
tageous where the article to be viewed is difEicult orexpensive to o~tain or maintain. rrhe holograms can be of
the ernbossed form so that they can be rapidly and cheaply
mass-produced. The image produced by the hologram retains
microscopic information.
If the above described process Eor forming a multicoloured
surEace relief hologram is employed then the mask or
filters required for reproducing the image can be incor-
porated witl~in the viewing apparatus of figure 2 or~
alternately, can be included in the hologram device o~
Figure l.
It has been found tllat the light that is diffracted by the
grating but which remains undiffracted by the hologram
emanates from the screen at angles causing possibly
undesirable illumination outside the viewing apparatus.
This potential disadvantaye may be overcome by the provl-
sion of an additional layer of venetian blind film. The
additional venetian blind film should have slats extending
perpendicularly to the surfaces of the film with the slats
being sontinuous along the width of the film. This addi-
tional film must be placed between the hologram and the
person viewing the reconstructed image and the film is
therefore secured in a spaced apart face to face relation-
ship with the front oE the screen. The holoyram to be
viewed is inserted between the screen and the additional
venetian blind film.
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The additional venetian blind film could be added to the
described ~ologram device.
The invention further provides an article useful in the
manufacture of hologram devices. This article is a
5 venetian blind film embossed or bonded on one side with a
plane grating. Additionally, if the article is to be used
in foeming multicoloured holograms it may be possible to
include the required mask or filters as part o~ the
article.
