Three - University of Arkansas Physics Department

Three-dimensional color holographic display
Brian P. Ketchel. Christy A. Heid, Gary L. Wood, Mary J. Miller, Andrew G. Mott,
Richard J. Anderson, and Gregory J. Salamo
Threedimensional (3D) color holograms are recorded in a ceriumdoped, strontium barlurn mobate
(SBN:60) photorefractive crystal. These holograms are shown to reconstruct true color reproduchons of
the original object with an observable field of view of 37". Angle multiplexing of two or more 3D color
holograms is also demonstrated with angle tuning of the reference beam corresponding to a separation
angle between stored images of 0.082". Each of these results is compared with correspond~ng theoretical
predictions. 6 1999 Optical Society of America
OCZS codes: 090.2870, 100.6890, 190.5330, 090.4220.
1. Introduction
The possibility of storing a three-dimensional (3D)
image library holographically in a small crystal has
long attracted the attention of researchers. This attraction
is driven by the fad that, among the many
3D image display techniques, holography provides
the most pleasing 3D images for the human eyebrain
system. Applications of holography to cinematography,
artificial intelligence, and security have
long been a goal of scientists and engineers. AIthough
progress toward this goal has been slow, recent
experiments have clearly demonstrated the
potential of photorefiadive crystals for real-time
storage and retrieval of 3D images.' Moreover, the
potential for storage and reconstruction of 3D images
has been demonstrated with freedom from distortion.=
hgh resolution,4 large depth of field,5-7 and
wide field of view (F'OV).a In this paper we report
the demonstration of the corresponding storage and
retrieval of multiple 3D color images. These images
are shown to have a wide FOV as demonstrated by
movement of one's head back and forth during viewing
of the hologram or by use of an imaging lens with
a color CCD camera to record the 3D image from
B. P. Ketchel. C. A. Heid, G. L. Wood, M. J. Miller
(mmille&arl.miI), and A. G. Mott are with the U.S. Army Research
Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783-
1197. R. J. Anderson is with the National Science Foundation,
4201 Wilson Boulevard, Arlington, Virginia 22230. G. J. Salamo
is with the Department of Physics, University of Arkansas, Fayetteville,
Arkansas 72701.
Received 23 February 1999; revised manuscript received 18
June 1999.
0003-6935/99/296159-08$15.00/0
6 1999 Optical Society of America
different perspective views. The obsercei FOV, ~ c -
curacy of color, resolution of multiplexed images, and
storage time are found to be in excellent agreelpent
with theory.
Our approach to color 3D holographic storage is
based on four-wave mixing in photorefractive crystals.9
The term photorefractive is used to describe a
special kind of optically induced refii~ctive-index
change that can occur in electro-optic materials.
The microscopic details of the photorefrqctive mechanism
are normally described by use of a band transport
model,lO-I2which assumes the existeuce of a pool
of charges residing in low-lying traps. When a spatially
varying intensity pattern is produced at a'photorefractive
medium, photoexcitation of the trapped
charges occurs at the maxima of the spatially varying
intensity pattern. The photoexcited charges ,migrate
by drift or diffusion out of the illulninated regions
and are eventually retrapped in the dark
regions of the crystal. The charge I..J .: --or7 +n
results in a spatially varying charge distl.itutiori th,~
is balanced by a strong spacexharge field according
to Poisson's equation. This strong electrostatic field
(Eo - lo4 V/cm) then produces a change in the refractive
index (An = 0.0001) through the electro-optic
effect, and a phase hologram is written.
In the case of holography the spatially varying in-
tensity pattern is produced when a reference beam,
Eref, is interfered with light scattered off of the objekt,
Eob,, which itself may be thought of as a summatin.
of plane waves. As long as these plane waves$nd
the reference beam are mutually coherent and 'the,
photorefractive storage crystal has suffici~.nt photorefractive
response at the laser wavelength along with
low dark current, interference of Emf and E, in the
crystal will yield a refractive-index grating propor-
10 October 1999 / Vol. 38, No. 29 / APPLIED OGjrICS "6159
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