TECHNICAL PROPOSAL

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00873A002000010056-1
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 47
• Document Creation Date: December 28, 2016
• Document Release Date: November 8, 2012
• Sequence Number: 56
• Publication Date: March 1, 1965
• Content Type: REPORT

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STAT
UCorni~g Glass Works
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CORNING GLASS WORKS
THE UNITED STATES EOVERNMENT
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Investigation of Improved Screens
for Rear Projection Viewers.:
March 1965
Corning Glass Works
Electronic Products Division
3900 Electronics Drive
Raleigh, North Carolina 27604
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I. INTRODUCTION
B. Company Background in Optical-'Technblogy
C. Materials Background
1. Photosensitive'Glass'
2. Porous Silica Glasses
3. Sintered Glass (MULTIFORM)"
D. Company Experience
1. Photosensitive Glass'
2. Porous Silica Glass
3. Sintered Glass (MULTIFORM)
4. Optical Glass
E. Attack to be Followed
III. TECHNICAL DISCUSSION
A. Introduction
1. Definitions
a. Projection and.Measurement Units of Light
b. Brightness
Rear Projection.-Screens.,
a. State-of-the-Art
b. Performance
3.
B. Materials Approach to the?.Problem.?.
1. Passive Screens ? ?
f. Fiber Optics
g. Porous. Vycor
d. Opal Glasses
e. MULTIFORM Glasses.'
a. Photosensitive- Glass.
b. Heterogene ous.:...Materials;
c. Polarizing Materials
Hybrid Screens
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IV. RECOMMENDED PROGRAM
V. PERSONNEL
VI. FACILITIES
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A. 'Objective
Corning Glass Works wishes to'propose that a study be made
of the various *glass and glass ceramic materials which may
prove of value as basic materials for constructing improved
rear projection screens. The'work that will be done will
include only available materials and processes. Thus, what-
ever success is achieved will be transferable with little
delay to practical screens. Small excursions into variations
of existing materials will be made as necessary to point the
directions for further work.
This proposal is written in response*to the "Development
Objectives, Improved Screens for Rear Projection Viewers"
dated March 17, 1964.
'B. Background in Optical. Technology
Corning has a broad background in'optics stemming from over
a half century experience.as a supplier of optical glass for
scientific, signal, and ophthalmic applications. Some recent
projects which have required an excellent knowledge of optical
technology are the production of massive optics for Schlieren
windows and for aerial camera lenses. Currently, work is
being conducted in the Electronics Laboratory at Raleigh
in the field of holographic images.' This has led to the
generation of a high degree of competency in handling
coherent light as well as the acquisition of some highly
precise optical apparatus. This is, discussed more fully in
a later paragraph on "Facilities".
Materials Background
While Corning's demonstrated abilities in optical technology
are important to the success of this project, perhaps the
greatest contributions the. Company.. can make is in the field
of materials technology. :Prior work, as reported by Bausch
and Lomb (1), has consisted of evaluating conventional
diffusing surfaces. Part of the work proposed herein will
also consist of evaluation but it. will be on surfaces and
bodies which are unique and which are created by selective
molecular changes in the material itself. It is recommended
that this initial study be. limited'to available materials
which have never been examined for their optical and diffusion.
properties. The conventional', and exotic optical glass are
obvious candidates for such a study. In addition there are
other Corning materials . whose' optical properties can be
altered by what might be called, molecular manipulation.
There are two general categories of such glasses and glass
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b. Processing ?
Practical glasses of these types have their
greatest sensitivity-.in..the ultra-violet.
Exposure through UV transmitting negatives
can result in: the formation of latent images
in the.glass with photographic accuracy and
resolution. Since the.glass sections
generally employed have. significant thickness,
and because'the nucleating process takes place
throughout the entire'.volume, it is for most
applications.essential'to have parallel light.
The latent image is then "developed" by heat
treating for minutes.or hours at several
hundred degrees centigrade.
Depending on the combination of exposure and
thermal treatment, a variety of property
changes can be'. created. If the integrated
.treatment'forms only colloidal metal particles
in the glass,.'a range of transparent colors
from red to blue will result. The colors may
be made so saturated that transparency is lost.
Another result of certain combinations of
treatments is''the 'rowing'of crystals around
the nuclei which, by light diffusion, form a
white opaque phase. .In addition to promising
interesting. optical possibilities, this phase
is also comparatively.-soluble in hydrofluoric
acid." Since?.the opal phase formation is a
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ceramics which would seem to offer the most promise.
1. Photosensitive Glass '
a. Unique Characteristics
Photosensitive glass,?as the name implies,
is sensitive to light. In compounding such
glasses, the photosensitive metals, gold,
silver or copper are introduced. In addi-
tion, other materials. known as "optical
sensitizers" and "thermal-reducing agents"
are included.. Such compositions typically
respond to exposure to-certain wave lengths
by forming small colloidal metal particle
nuclei. Subsequent heating of the glass
then encourages the'growth of small crystals
around the nuclei.
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volume effect-it.is possible to selectively
etch it away creating ' cavities or holes
with accuracy and resolution limited mainly.
by the negatives . used. for exposure.
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Detailed studies have. been made of the forma-
tion of the opaque etchable phase. For
practical'consideration in processing, the
optimum sized ' crystal. is 4 - 5 microns.
Recognizing now that subsequent cycles of
exposure, heat treatment and etch may be
employed, it.is evident that one can create
an unlimited. combination of optical paths
through the screen.
2. Porous Silica Glasses
Certain glass compositions in the borosilicate family,
upon heat treating,'.will separate into two phases; one,
a silica network and the 'other a composition soluble
in hydrochloric. acid. This soluble phase can be leached
away leaving a 'rigid cellular permeable structure.
The pores in this.,le.ached body are twenty to forty
angstrom units in.dameter.. The void volume amounts
to about 30% of'..the'.:total. The whole body need not
be leached. Interesting optical effects have been
produced by leaching-only.a thin surface layer and
impregnating with'other.substances.
3. Sintered Glass :.' . ' . '. '
Glasses of many compositions. can be finely powdered,
pressed into desired shapes,. and reconsolidated by
sintering. The resultin'g.articles are vitreous and
can be clear or opaque,. depending on the method of
firing. Again, depending'on processing., the bodies
may be completely impervious-or may have a degree of
porosity. Pore-sizes can be'controlled to maximum
values ranging from.l:4.to 220 microns.
JD., Company Experience
Photosensitive Glass'
While present automatic processing equipment limits one
dimension of any article to 16", large aperture masks
for 21" color TV tubes were.one-time made. These
contained hexagonal holes-of 0.008" diameter on 0.028'!
centers. The 21" mask had over 500,000 holes. Fine
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-4/0 109(' screens of*300 mesh have been made routinely and
`1000 mesh has been made on a laboratory basis.
Since these required through holes they were
necessarily quite thin, limiting their overall
dimensions to about.'a 2" circle. If only surface
indentations were required, the overall size would
be limited only by the glass forming and handling
equipment.. A concurrent project at the Bradford
facility involves photosensitive glass in the half
tone printing process.- Reticulated surfaces of 150
-ine pairs per inch. are being used. This does not
in any way tax the capability-of the material.
2. Porous Silica Glass...
Corning has manufactured and.sold porous glass, for
a number ofyears, for use in applications where
moisture-gettering is required. Some experience has
been gained in impregnating with various materials
but there are no standard products manufactured.
Sintered Glass (MULTIFORM)
Products made by this process have been marketed for
over ten years. A plant in-Corning, New York, is
devoted entirely to:MULTIFORM. A great range of glass
properties and geometries can-be realized.
4. Optical Glass
Hundreds of glass compositions of a great range of
optical properties are melted in the Company's
Herrodsburg, Kentucky, plant. Sizes range from
blanks for opthalmic lenses to radiation shielding
windows weighing tons.
E. Attack to be Followed
The project will be divided into three phases, the first
of which will be a study of all available literature. The
second part will be the theoretical investigation in which
the many theories of light. scattering are reviewed for
applicability and relate' to the properties of available
materials. Finally, the most feasible approaches will be
tested experimentally.
Throughout the course of the work documentation will be
maintained and periodic reports wi?ll.be submitted.
While the major effort will be 'on ?.the applications of
available materials, the need for,-and properties of new
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materials will be given attention.','Concepts for active
screens will also be considered;.-should'they arise.
At the conclusion of 'the first two phases, it would be
considered desirable to confer with'~the' contracting agency
bef ore going on to the next step.
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of 1
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The theoretical study is expected to..indicate what features of the
available materials will be.of the greatest value in achieving the
objectives. The experimental part of'the project will provide the
opportunity to test the theoretical: conclusions. It is entirely
possible, too, that the experimental'-wo.rk may yield some un-
expected beneficial properties that'can.,be used to enhance the
theoretical approach. " '?
OF
It is expected-to be,possible to combine.the desirable properties
to optimize the performance against, the?,:ob.jectives for, appearance, ?
efficiency, contrast and resolution'. It. is impossible, at this time,
of?course, to predict with great accuracy';how'closely all the ob-
jectives will be met and what trade-offs?may have to be made. It
would be desirable to discuss this.with'-the contracting agency at
the proper time.'
II. RESULTS EXPECTED
In the course of the experimental work,-'samples will be built for
evaluation which later can be turned over 'to the contracting agency.
Where-exceptionally good results are realized every effort will be
made to provide the agency with.;a practical sized sample.
It is not unreasonable to expect that new concepts for active screens
will evolve as the work progresses.. The materials requirements would
.. very. probably be beyond the'scope of the present project. Due note
-will be made should such an.occasion..ari'se which could serve as the
.--basis for Corning initiating new materials research and possibly
providing the base for- a subsequent . pro:jec:t.
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Rear projection is a technique employed in visual presen-
tations, where an observer`is'located on one side of a
tranaluoent and dlffusing'screen;.''and the optical image
projector on the other. Well-known examples are view
cameras, reflex cameras, microfilm readers, background
scenes in motion.pictures and certain electronic data
displays. The observer has a certain amount of freedom
to move around while observing the''display and does not
run the risk of interposing himself between the projector
and the screen, which would'causea shadow and loss of the
display.
However, the advantages of: rear .pr;ojection over front
projection, in which observer-and--projector are on the
same side of the'screen, are obtained: at the expense of
reduced brightness, viewing angle..,,picture definition,
contrast and tolerance of ambient illumination. Except
for a recent study carried out by Bausch and Lomb. (1),
relatively little quantitative.data.,ar'e available about the
diffusion characteristic of available rear projection
screens. This .s an area where pirical techniques have
yielded oo fnr cnma in=a ized applications
in the ,past",: but where a thoroiz_gh'scientific s udy of new?
materials'may st;ll_be expected to yield significant
improvements,
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1. Definitions
The following two subsections deal with the
projection of light and some',general re-
lationships encountered.in.the:measurement
of light intensity and brightness..
a. Projection and. Measurement Units of Light
-The function of a light, projector is to
gather as much':light a ,s, possible from the
light output'of a suitable source and-to-
project this light into a desired direction.
Since an imaging capability is also'required,
the optical system is '.somewhat more complicated
than that of a'simple light collimator. A
typical`projection system (2) is shown
schematically in Fig..'.1.
'The intensity of the projected light is
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measured in.terms of foot-candles. This
is the most commonly used photometric unit.
To gain a quantitative. feeling for this
intensity; or;illumination, it is helpful
to recall, that the-maximum illumination
outdoors due to both sunlight and sky light
is approximately.10',000 foot-candles. This
may range.. down :to 1.,000 ,and 100 foot-candles
for dark or very dark.days (3). Indoor
levels of` illumination are of the order of
10:-20 foot candles....
The'f oot-candle is'derived from the basic
unit for the'lunimous.output of a lamp, the
candela,-which.in turn,-is defined as the
sixtieth part.-of the Xntensity of a square
centimeter of-a black body radiator at the
the temperature of-freezing platinum (2047? K)
A light source of:-one candela output, which
radiates light,equally''in all directions,
will produce an illumination of one foot-
candle, or one lumen per square foot, at
the surface of 'a .'sphere, which is concentric
with the , source)" and .which has a radius of
one foot.. At' a. distahce of, one meter, the
illumination will be.one'.lumen per square
meter, or one lux. These relationships are
shown graphically' in- F g..2.
Since the concept. of'light involves the
.sensitivity response';of:the human eye, there
is no `one-to-one equivalent between light
intensity and'power'denisity as one is
accustomed to.in other'por'tions of the
electromagnetic spectrum.- Futhermore,
light is almost never;' monochromatic, as
microwave radiation;'for example, usually is.
However, it is useful' :to remember the re-
lationship at' the. wavelength of peak visual
sensitivity, namely' 555.millimicrons, where
one watt corresponds-to approximately 682
lumens.
.The light projector is used in conjunction
with some screen whi.ch.intercepts and displays
the image contained'in?the'projected light
beam. The total amount 'of ' light thus inter-
cepted is the' product .of .the average illu-
-mination in foot-candles. and the screen area
in square feet, i.e.,'.:
Total light (1m) = AVg. Illum, (ft-c) x
Ilium, Area. (s~ft):. ,,
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The human eye.. does not see light or illumination
itself. Rather.,.it.se.es reflected or emitted
light from area sources. Unlike' illumination,
brightness does not change with distance from
the surface 'those brightness the eye is per-
ceiving. ?This.is so because the eye is not
only an imaging system, but also the optical
equivalent of-:'an extremely high-gain (in
excess of 80 db) antenna through its resolving
power of less than one. minute of arc. Thus,
although the power received from an elemental..
area of the surface decreases as the square of
the distance`,., the area'on.the retina correspond-
ing to that elemental surface portion also de-
creases in the same measure. Hence, the power
density, or. illumination, on that part of the
retina remains the same..
The.measure for brightness is the foot-lambert.
It is the brightness of.a surface which emits
or reflects perfectly diffuse light at the
rate of one: lumen per square foot of area. In
the case of the perfectly reflecting and dif-
fusing. ' screen; 'this, means a brightness of one
.foot-lambert per foot-candle of incident il-
luminati on..
The term "'perfectly: diffuse" light refers to
the.light emitted or reflected by a surface
which'obeys.the Lambert~Cosine Law. The
light-intensity i's-proportional to the cosine
of the angle between the direction of emission
and-the normal to.the?surface. An element of
a surface.which obeys.-this law will appear
equally bright. when .observed from any direction.
Minimum brightness for-.good pictorial repre-
sentation is of the .order of 10 foot-lamberts
for the brightest 'spots'--of the image, and
0.1 foot-lamberts.: for? -the darkest spots,.
corresponding?to.a contrast ratio of 100 to' 1.
Non-image (background-?or ambient) illumination
should'result.in'a.brightness not. exceeding
0.02 foot-lamberts."` A; contrast ratio of 25 to
1 is sufficient for.-.positive printed or line
material, and`. :a ratio .6f 5 'to 10 to .1 for
negative.-(white letters on black background)
print..
: ' . .
For?'higher ambient brightness such as the 5
foot-lamberts mentioned in-the development.
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objectives, the contrast ratio will have to
be considerably higher.-'
Rear Projection Screens
Most ' of the work which. has thus far been
done to develop high-quality rear projection
screens has been in trig ,area of large
displays. The best known example of this
nature are the very large (up to 40 x 80 ft.)
screens used for background scenes during the
filming of motion pictures. Wide use is
made of such techniques as Fresnel screens and
lenticular screens (6). Optimum procedures
have been worked out to arrive at solutions
fitting the sometimes conflicting requirements
regarding screen brightness, contrast, re- .
flection factor, gain,. bend angle and picture
size, to' the limitations dictated by ambient
light, projection'lens focal length and
projector lumen output.-(5).
The field of small display rear projection
systems with its different requirements has
received much. less attention. This encompasses
primarily view cameras and microfilm readers e
The requirements in-these display systems
have been not..nearly as demanding as in large
displays. Among the reasons for this are:
a) lower power,.and hence lower
efficiency requirements, because
of the small screen size.
lower tolerance to ambient light
..was required, because the equipment
could be operated in a darkened
room (film. reader), or special
measures could be taken to eliminate
ambient light.(e.g.,, photographer's
:cloth used in. view cameras).
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c)` less stringent requirements in terms
-of..unirorm.diffusion and large bend
.angle,:because the screen was usually
;. viewed. by only. one observer who
could adjust his position to attain'
optimum location and view angle.
The main concern in..the technical perfection of these
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small screens has been to provide uniform brightness -
,in the direction of the observer. across the entire
screen. This is usually-'don'e- with a thin Fresnel
lens in contact with the back surface which has the
effect of bending the gaih.:lobe of the diffused light
toward the observer. A good deal-of development work
still remains to be done to achieve higher efficiency
and uniform diffusion over' a- larger angle. In most
conventional screens thes.e..requirements conflict,
but this need not be so from-..a theoretical view point.
Some analysis work is required to better understand
-and improve the scattering, process and will be
carried out in the course.of this study.
In rear projection screens one is primarily
interested in.the diffusely transmitted light,
rather than in the diffusely reflected light
which is important in-front projection screens.
Aside from that,'the technical considerations
are quite similar. The overall efficiency of
rear projection screens is significantly lower
due to transmission and scattering losses, as
well-as due to the portion of the light
reflected from the front surface, which is
completely lost for the rear projection display.
The concept of a perfectly diffusing reflector
may also be applied.to the case of rear pro-
jection. There,.the ideal case would be a
surface which.exhibits a uniform brightness
of one foot-lambert regardless of viewing angle
for each foot-candle of incident illumination
from the other side. Such a perfectly diffusing
screen is said to have a gain of unity. In
practice, most surfaces-have a higher brightness
when viewed from certain directions, with a
necessarily lower brightness when viewed from
other directions. The gain in each direction
is defined as. the ratio . of observed brightness
in foot-lamberts to- incident illumination in
foot-candles:..
Gain = foot-lamberts/foot-candles
This is illustrated for atypical rear-projection
screen in Fig. 3.
The observers, depending on whether they are in a
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direct line with'the.pr.ojector (Observer 1),
or looking at the screen at a more or less
large.angle with-this principal axis, see a
brightness.corresponding, in this example,
to a screen gain "of 3;,. 1.4 and 0.4 for
Observers 1,2, And-3i respectively. The
gain falls off with increasing angles from the
principal axis because ',of imperfect diffusion
in the screen. This is indicated by the length
of the arrows. The' d'i'stribution lobe for a per-
fectly diffusing 'screen would be a circle. The
illumination at point A"in this example was
-.assumed to be-10 foot-candles. The angle
between the observe'r's direction of view and
the principal axis. .is .called bend angle. The
gain as a function of.the'bend angle is shown
for a number of practical.screens (5) in Fig. 4.
The lowest curve"in',Fig. 4 shows almost uniform
gain; hence this.screen.is an almost perfect
diffuser. However,'the fact that the gain is
much less than unity'indicates the losses which
are invariably present-in-the rear projection
case. These are due to reflection on the projector
side, and to absorption'in the screen. Usually,
low absorption, or.high-transmission (80-90%),
is accompanied by low' diffusion (high gain) and
vice versa. Thus, the 'desirable goal of both
high transmission and high diffusion is usually
not attained in one ancl.the same screen. Some
useful development work...toward reaching a com-
promise between these?two.usually conflicting
requirements can still be done, and will
constitute one of the: major aspects of the task
to be carried out.
-A useful figure of merit for rear projection
screens is the bend ahgle.at which the gain has
fallen to 50% of its peak value. This is similar
to the half-power'beam width familiar from micro-
wave and optical collimation systems. Similarly,
the one-third'power angles can be established.
Usually, the higher the?peak gain,. the lower
the 50% and 33% bend-angles. These relationships
are plotted for typical screens in Fig. 5, which
also contains-.a typical graph of reflection factor
vs peak gain. The latter is the ratio of re-radiated
to incident ambient illumination on the observer
side of the screen. Hence, the lower the reflection
factor, the greater-the tolerance of the screen to
ambient (room) light.'
Theoretical-Considerations '
The proposed development study on new or improved rear
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projection screens will involve not only experimental
work, but also, and.-perhaps.. more.importantly, a
thorough. theoretical investigation of the basic
mechanisms involved.'.in the. transfer of the image from
the projector to the. observer side of the screen, and
the diffuse reradiation of the image on the observer
side. In addition"-.*, a- literature and patent search
wl e conducted.-TS-e. ec anism of dif usion may
be brought about in::two principally di eren a
First, one may consider'the case of a material which
is heterogeneous throughout-:. A simplified model is
that of a-clear, transparent host material, which has
suspended in it a random. arrangement of spherical
particles of. a refractive 'index different than that of
the host material. .The resulting scatter properties
are governed by turbidity of the material has been
investigated by Mie;;..(7),,for-.a 'density' of N spheres of.
radius R.per unit volume:..:..:. :
and A 1 = )/n, , the.wavelength of the light in the
medium. The expression:?f(x)'-.'in Equ. (1) is a compli-
cated function for which-the-following extreme cases
f(x) x
f (x) d- x
f (x) 2
for-.,-x. < c
1
(3)
for : x
1.
(4)
for 'x'~.
1
(5)
Equ. (3) is the well-known result for Rayleigh
scattering by particles small compared to the wave-
length. The'scattering-is proportional to the inverse
fourth power of,the wavelength.'.
For the diffusing screens., considered in this study,
cases (4) and (5) will be of.greater interest. The
latter is usually referred to.as Mie scattering, caused
by particles large compared'.to'the wavelength. Its
principal characteristic,is:';thb .fact that it is' non-
dispersive-, i.e the sattei.nc dog e
wavelength. As a conseque ce-,_color nf ormat on-is,_
,o,
preserved.
Declassified in Part - Sanitized Copy Approved for Release 2012/11/08: CIA-RDP79B00873AO02000010056-1
 Li
HI
fl
7
n i
Declassified in Part - Sanitized Copy Approved for Release 2012/11/08: CIA-RDP79B00873AO02000010056-1
and formulae.
The other main .diffusion mechanism is through
treatment of the surface (front or back, or both).
Frosted glass is one example'.- The scattering or
diffusion here depends on the so-called Rayleigh
Criterion.concerning.the diffuse reflection from
rough surfaces as a?-function of the incident angle.
An analytical method'to?'des.cribe screen properties
has been'proposed'by Hill.(8). Following the notation
of Sears-(g)- one may state. the, following definition
Definitionsi
F, luminous flux;.....
I, luminous intensity or'flux per unit solid angle;
B, luminance (brig'htnes.s)'i
E, illuminance or'.flux per?'unit area received at
a surface; and-.*..,
L, luminous emittance or total flux emitted per.
Defining equations:
I = DF -where w is
solid-angle with vertex at source;
da , where. B ::is angle with normal
dw
0.
E = df I,& Cos
B = ' A I O : ; :. and
r 2
to-surface;.
A A cos 6
L= 4F , F is
pA
total.'emitted flux.
The essence of Hill's method'is the use of an empirical
"shape factor" s to-'..modify Lambert's law. The following
equations compare intensity snd brightness for a surface
which follows Lambert's law;. with one which is direc-
tional but-for which the intensity falls off in
proportion to some.power s:.of the, cosine of the angle
with the normal to the: surface.. '
IB Io cos O I 8 = Io coss A
Lambert Surface 'Directional Diffuser
B g = . BL Be = BD cos
Here BL represents the' brightness of the Lambert surface,
and BD the normal brightness. of.the directional surface.
Declassified in Part - Sanitized Copy Approved for Release 2012/11/08: CIA-RDP79B00873AO02000010056-1
 Declassified in Part - Sanitized Copy Approved for Release 2012/11/08 CIA-RDP79B00873AO02000010056-1
The illuminance of 'flux received per unit area at a
point not on the screen illuminated by a circular
area of the screen whose center is at the foot of
the perpendicular from the point and whose radius
subtends an angle X at the point is found by
integration to be;
EL = BLsin2 d