We report the growth and characterization of a new photorefractive material, potassium lithium tantalate niobate (KLTN). A KLTN crystal doped with copper is demonstrated to yield high diffraction efficiency of photorefractive gratings in the paraelectric phase. Voltage-controllable index gratings with n, = 8.5 x 10^-5 were achieved, which yielded diffraction efficiencies of 75% in a 2.9-mm-thick sample. In addition, diffraction was observed in the paraelectric phase without an applied field. This effect is attributed to a growth-induced strain field

Agranat, Aharon

Hofmeister, Rudy

Yariv, Amnon

English

Caltech Authors - Main

May 15, 1992 / Vol. 17, No. 10 / OPTICS LETTERS 713
Characterization of a new photorefractive
material: Kl-yLyT 1-xNx
Aharon Agranat
The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Rudy Hofmeister and Amnon Yariv
California Institute of Technology, Pasadena, California 91125
Received January 15, 1992
We report the growth and characterization of a new photorefractive material, potassium lithium tantalate nio-
bate (KLTN). A KLTN crystal doped with copper is demonstrated to yield high diffraction efficiency of pho-
torefractive gratings in the paraelectric phase. Voltage-controllable index gratings with n, = 8.5 x 10-5 were
achieved, which yielded diffraction efficiencies of 75% in a 2.9-mm-thick sample. In addition, diffraction was
observed in the paraelectric phase without an applied
strain field.
The use of photorefractive materials to store volume
holograms for optical computing and optical mem-
ories has long been an active area of research.` 3
In addition, these materials show promise in the im-
plementation of optical neural networks.
Potassium lithium tantalate niobate
(K1-YLYT1-xNx) forms a solid solution for y c 0.15.
Nevertheless, most research has been concentrated
on the end members KLT4'5 and KTN.6'7 In gen-
eral, most compositions of the solid-solution series
have received little attention, possibly because they
are considered difficult to grow.
We were able to grow large optical-quality crystals
of KLTN using the top-seeded solution growth
method by carefully choosing the constituent con-
centrations of the flux. Our primary motivation
for adding lithium to KTN was to achieve a room-
temperature phase transition 8 with a lower niobium
concentration than that in conventional KTN's.
Secondarily, the lithium ion is expected to be more
mobile than the potassium ion that it replaces and is
expected to weaken the transition from first order
to order disorder.9
KLTN has the perovskite structure. In its
highest symmetry phase it is cubic and, for small
lithium concentrations, undergoes transitions to
tetragonal, orthorhombic, and rhombohedral struc-
tures with decreasing temperature. 10 In our experi-
ments the crystal was maintained just above the
paraelectric/ferroelectric transition.
In the cubic phase the material's photorefractive
properties are described by the quadratic electro-
optic effect."1 The birefringence is given by
3An = n0 gp2,
2
P = eo(e - 1)E, (1)
where g is the relevant quadratic electro-optic coef-
ficient, no is the index of refraction, and e is the di-
field. This effect is attributed to a growth-induced
electric constant. P is the induced dc low-frequency
polarization that we assume is linear with E. In
this case, when an external field is applied to the
crystal, an index grating is written with
ni An[Eo + ESe(x)] - An(Eo)
-j0geo2e2[2EoE.,(x) + E.,2(X]
=>nleff = no3geo 2 e2 EoEs,(x), (2)
where ESC(x) is the space-charge field due to the in-
terfering light beams and Eo is the applied field.
n 1eff is the term of relation (2) that leads to Bragg
matching. The space-charge field is thus transpar-
ent to the interfering beams unless a spatially uni-
form field is applied. By using this property, we
have performed modulation of the nonlinear re-
sponse at 20-kHz rates.
In this Letter we discuss the material properties
of a KLTN crystal. We report a capacitive mea-
surement of the dielectric constant that indicates
that the KLTN undergoes a second-order phase
transition. Diffraction experiments performed
both with and without an applied field are de-
scribed. Finally, KLTN is indicated to be a promis-
ing new photorefractive material.
The sample used in the following discussion was a
6.8 mm X 4.9 mm X 2.9 mm piece cut from a crys-
tal grown by us using the top-seeded solution
growth method. The crystal was pale olive green
and free of striations. Its as-grown weight was
11.6 g. By using electron microprobe and atomic ab-
sorption analysis, the composition was determined
to be K0 .950Li004Tao857Nbo.1 29 :Cuo.004.
Figure 1 shows the absorption spectrum of the as-
grown sample with peaks at 370 and 585 nm caused
by Cul' donors and Cu21 traps, respectively. The
concentration of the impurities Cul' and Cu2" can
be determined from the absorption peaks by using
0146-9592/92/100713-03$5.00/0 © 1992 Optical Society of America
714 OPTICS LETTERS / Vol. 17, No. 10 / May 15, 1992
3.0
2.5-
s 2.0
'. 1. 
. 1.5
° 1.0
0.5.-
I'll
350 450 550 650 750 850 950 1050
Wavelength (nm)
Fig. 1. Absorption spectrum of the as-grown KLTN: Cu.
2.5E4 -
(a)
2.0E4
1.5E4
.9
' 1.0E4
5000.0-
1
8E4
6E4
4E4
2E4
50 160 170 180
Temperature (K)
190 200
tained at a temperature of 15 K above the transi-
tion. The writing argon laser beams were at either
488 or 514 nm. They were ordinary polarized to
minimize beam interaction. The diffraction effi-
ciency of the grating thus written was monitored
with a weak extraordinary-polarized He-Ne beam at
633 nm. The 633-nm beam was verified not to
erase the grating. The writing continued until the
maximum diffraction was achieved.
After the gratings were written, the crystal was
cooled to just above the transition, and the diffrac-
tion efficiency was determined as a function of ap-
plied field. The results are illustrated in Fig. 4.
The three curves shown are for gratings that were
written at +1450, 0, and -1450 V/cm. When the
grating was optically erased with the argon beams,
some residual diffraction (-1%o) remained that was
not optically erasable and could only be removed by
heating the crystal to room temperature.
The highest diffraction efficiency observed for
488-nm writing beams was 75% for a sample of
thickness 2.9 mm, where corrections were made for
Fresnel losses. For 514-nm writing beams, the
maximum value was reduced to 30%, and at 633 nm
the diffraction was almost undetectable. The writ-
(b)
. ' f \"In
k w-1| ... S~~~~
488nm Ml
T.C.
110 120 130
Temperature (K)
BS
140 150
Fig. 2. (a) Dielectric constant of the KLTO.85 7No.12 9. The
phase transition is -50 K higher than in a comparable
KTN. (b) Dielectric constant of KTO.86NO.13.
Beer's law.1 2 We calculate [Cu"] = 6.0 X 10 19/cm3
and [Cu2"] = 2.1 X 10l8/cm3 .
White-light birefringence measurements between
crossed polarizers were used to measure the effec-
tive quadratic electro-optic coefficients. We deter-
mined gl - 912 = 0.186 m4 C -2 to an accuracy of 5%.
The dielectric constant was monitored as a func-
tion of temperature by measuring the capacitance of
the crystal, where C = eoeA/d. The results, shown
in Fig. 2(a), are compared with those obtained from
a KTN crystal with a similar tantalum:niobium ra-
tio [Fig. 2(b)]. The cubic/tetragonal transition tem-
perature has been raised approximately 60 K, to
178 K. The FWHM, i.e., the temperature range
over which the dielectric constant drops to half its
maximum value, is increased to -10 K. Diffraction
due to the linear electro-optic effect was weak di-
rectly below the transition and grew steadily as the
temperature was lowered, indicating a second-order
transition.
The diffraction experiments with applied field
were performed as in Fig. 3 with the sample main-
/t"u Ccum LjJ dbfected
cr ost -t detector
Fig. 3. Experimental setup for measurement of diffrac-
tion efficiency. Photorefractive crystal Xtl is mounted in
a vacuum cryostat. Beam splitter BS and mirrors
MI and M2 create a 488-nm grating that is read with
the Bragg-matched 633-nm beam and mirror M3. Dif-
fraction is measured versus applied voltage Vo. The tem-
perature was monitored by thermocouple T.C.
U
C
Ui
a
-2400 -1600 -800 0 800 1 600 2400
Applied Field, V/cm
Fig. 4. Two-beam diffraction efficiency for gratings
written at +1450, 0, and -1450 V/cm.
/ L
'l ..
.( (\N
0
100
0
C0
0
.2
M
May 15, 1992 / Vol. 17, No. 10 / OPTICS LETTERS 715
ing times for maximum diffraction roughly followed
Twrite - 6 s2 cm2 W - light intensity incident upon the
crystal.
From the calculated index modulation of nj =
8.5 X 10', we determine the space-charge field to
be E,, = 150 V/cm. Using the writing time of 180 s
at beam intensities adding up to 27.2 mW, we esti-
mate the sensitivity for this KLTN crystal to be
7.30 X 10-6 cm3 /J for an applied field of 1.6 kV/cm.
Following the procedure outlined above, the erase
time near T, was up to 2 orders of magnitude
greater than the write time at T, + 15 K.
KLTN was also observed to display weak diffrac-
tion without an applied field at as much as 120 K
above the phase transition. At room temperature
the diffraction efficiency in a 3-mm-thick sample
was 0.65%. The effect was strongest with focused
beams and weakened as progressively larger areas
of the sample were illuminated. However, the dif-
fraction efficiency measured with a given beam
geometry was independent of beam intensity over
several orders of magnitude.
In the diffraction experiments performed, an
index grating was generated as in relation (2).
Thus the diffraction efficiency in the crystal is a
strong function of the dielectric constant E. The
largest effects occur near the phase transition. In
KLTN the lithium raised the transition tempera-
ture 60 K over that of a KTN cyrstal with similar
niobium concentration so that the temperature of
maximum response was correspondingly raised. By
choosing the proper niobium and lithium concentra-
tion, it may be possible to raise T, to near room tem-
perature while retaining a second-order transition.
As reported, the diffraction due to the linear
electro-optic effect was weak directly below the
transition and grew steadily as the temperature was
lowered. The fact that the linear electro-optic coef-
ficients are known to be large in this class of mate-
rials indicates that there is little spontaneous
polarization at the transition. In other words, the
transition displays second-order behavior and is at
best -weakly displasive. This agrees with KTN
studies in which the phase transition is reported to
become first order only for niobium concentrations
exceeding 30%o.1o
In the experiments of diffraction with an applied
field, the data are seen to follow a sin2 behavior with
saturation (Fig. 4). This saturation is at least
partly due to nonlinear polarizability of the medium
at high field strengths.6 From the data it is clear
that a compensating dc field of approximately
300 V/cm is induced in the crystal under the influ-
ence of the writing field. As described previously,
residual diffraction persisted when the gratings
were optically erased. Also the erase/write time
asymmetry was increased by up to 2 orders of mag-
nitude. The asymmetry in the erasure time close to
the transition may be due to the following mecha-
nism: It is well known that in these crystals dipo-
lar clusters are formed around impurities that move
outside the center of inversion. In the vicinity of
the phase transition the correlation length of these
clusters becomes large and their relaxation time in-
creases. Thus it is possible that a secondary grat-
ing is formed by these dipolar clusters in addition to
the normal space-charge grating. The erasure time
of the secondary grating is long in the vicinity of the
phase transition, and this causes the asymmetry.
This tentative explanation is currently under fur-
ther investigation. We hope to harness this effect
in the future to perform fixing in these materials.
In the experiments without an applied field, it was
observed that substantial diffraction only occurs
when the writing beams interfere over a small (uni-
formly strained) region of the crystal. We have
determined that the effect arises from a weak semi-
uniform strain that is due to the growth process.
In conclusion, we have demonstrated the growth
of a new photorefractive material, KLTN, and have
characterized its photorefractive properties.
Strong quadratic electro-optic coefficients, high dif-
fraction efficiences, and sensitivities of 7.30 x
10-6 cm3/J at 1.6 kV/cm were observed. Based on
this research, KLTN crystals seem to be highly
promising materials for volume hologram storage
applications. In addition, the aspect of voltage con-
trol leads naturally to various interconnect schemes
for neural networks.
This research is supported by the U.S. Army
Research Office.
References
1. P. J. Van Heerden, Appl. Opt. 2, 393 (1963).
2. D. Gabor, IBM J. Res. Dev. 13, 156 (1969).
3 D. Von der Linde and A. M. Glass, Appl. Phys. 8, 85
(1975).
4. Y Yacoby and A. Linz, Phys. Rev. B 9, 2723 (1974).
5. J. J. Van der Klink and D. Rytz, J. Cryst. Growth 56,
673 (1982).
6. A. Agranat, V Leyva, and A. Yariv, Opt. Lett. 14, 1017
(1989).
7. R. Orlowski, L. A. Boatner, and E. Kraetzig, Opt.
Commun. 35, 45 (1980).
8. K. Sayano, Accuwave, Santa Monica, Calif. 90404
(personal communication, 1990).
9. R. L. Prater, L. L. Chase, and L. A. Boatner, Phys.
Rev. B 23, 5904 (1981).
10. C. M. Perry, R. R. Hayes, and N. E. Tornberg, in Pro-
ceedings of the International Conference on Light
Scattering in Solids, M. Balkansky, ed. (Wiley, New
York, 1975), p. 812.
11. A. Agranat, K. Sayano, and A. Yariv, in Digest of
Meeting on Photorefractive Materials, Effects, and
Devices (Optical Society of America, Washington,
D.C., 1987), paper PD-1.
12. V Leyva, Ph.D. dissertation (California Institute of
Technology, Pasadena, Calif., 1991).


Characterization of a new photorefractive material: Kl-yLyT1-xNx

May 15, 1992 / Vol. 17, No. 10 / OPTICS LETTERS 713
Characterization of a new photorefractive
material: Kl-yLyT 1-xNx
Aharon Agranat
The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Rudy Hofmeister and Amnon Yariv
California Institute of Technology, Pasadena, California 91125
Received January 15, 1992
We report the growth and characterization of a new photorefractive material, potassium lithium tantalate nio-
bate (KLTN). A KLTN crystal doped with copper is demonstrated to yield high diffraction efficiency of pho-
torefractive gratings in the paraelectric phase. Voltage-controllable index gratings with n, = 8.5 x 10-5 were
achieved, which yielded diffraction efficiencies of 75% in a 2.9-mm-thick sample. In addition, diffraction was
observed in the paraelectric phase without an applied
strain field.
The use of photorefractive materials to store volume
holograms for optical computing and optical mem-
ories has long been an active area of research.` 3
In addition, these materials show promise in the im-
plementation of optical neural networks.
Potassium lithium tantalate niobate
(K1-YLYT1-xNx) forms a solid solution for y c 0.15.
Nevertheless, most research has been concentrated
on the end members KLT4'5 and KTN.6'7 In gen-
eral, most compositions of the solid-solution series
have received little attention, possibly because they
are considered difficult to grow.
We were able to grow large optical-quality crystals
of KLTN using the top-seeded solution growth
method by carefully choosing the constituent con-
centrations of the flux. Our primary motivation
for adding lithium to KTN was to achieve a room-
temperature phase transition 8 with a lower niobium
concentration than that in conventional KTN's.
Secondarily, the lithium ion is expected to be more
mobile than the potassium ion that it replaces and is
expected to weaken the transition from first order
to order disorder.9
KLTN has the perovskite structure. In its
highest symmetry phase it is cubic and, for small
lithium concentrations, undergoes transitions to
tetragonal, orthorhombic, and rhombohedral struc-
tures with decreasing temperature. 10 In our experi-
ments the crystal was maintained just above the
paraelectric/ferroelectric transition.
In the cubic phase the material's photorefractive
properties are described by the quadratic electro-
optic effect."1 The birefringence is given by
3An = n0 gp2,
2
P = eo(e - 1)E, (1)
where g is the relevant quadratic electro-optic coef-
ficient, no is the index of refraction, and e is the di-
field. This effect is attributed to a growth-induced
electric constant. P is the induced dc low-frequency
polarization that we assume is linear with E. In
this case, when an external field is applied to the
crystal, an index grating is written with
ni An[Eo + ESe(x)] - An(Eo)
-j0geo2e2[2EoE.,(x) + E.,2(X]
=>nleff = no3geo 2 e2 EoEs,(x), (2)
where ESC(x) is the space-charge field due to the in-
terfering light beams and Eo is the applied field.
n 1eff is the term of relation (2) that leads to Bragg
matching. The space-charge field is thus transpar-
ent to the interfering beams unless a spatially uni-
form field is applied. By using this property, we
have performed modulation of the nonlinear re-
sponse at 20-kHz rates.
In this Letter we discuss the material properties
of a KLTN crystal. We report a capacitive mea-
surement of the dielectric constant that indicates
that the KLTN undergoes a second-order phase
transition. Diffraction experiments performed
both with and without an applied field are de-
scribed. Finally, KLTN is indicated to be a promis-
ing new photorefractive material.
The sample used in the following discussion was a
6.8 mm X 4.9 mm X 2.9 mm piece cut from a crys-
tal grown by us using the top-seeded solution
growth method. The crystal was pale olive green
and free of striations. Its as-grown weight was
11.6 g. By using electron microprobe and atomic ab-
sorption analysis, the composition was determined
to be K0 .950Li004Tao857Nbo.1 29 :Cuo.004.
Figure 1 shows the absorption spectrum of the as-
grown sample with peaks at 370 and 585 nm caused
by Cul' donors and Cu21 traps, respectively. The
concentration of the impurities Cul' and Cu2" can
be determined from the absorption peaks by using
0146-9592/92/100713-03$5.00/0 © 1992 Optical Society of America
714 OPTICS LETTERS / Vol. 17, No. 10 / May 15, 1992
3.0
2.5-
s 2.0
'. 1. 
. 1.5
° 1.0
0.5.-
I'll
350 450 550 650 750 850 950 1050
Wavelength (nm)
Fig. 1. Absorption spectrum of the as-grown KLTN: Cu.
2.5E4 -
(a)
2.0E4
1.5E4
.9
' 1.0E4
5000.0-
1
8E4
6E4
4E4
2E4
50 160 170 180
Temperature (K)
190 200
tained at a temperature of 15 K above the transi-
tion. The writing argon laser beams were at either
488 or 514 nm. They were ordinary polarized to
minimize beam interaction. The diffraction effi-
ciency of the grating thus written was monitored
with a weak extraordinary-polarized He-Ne beam at
633 nm. The 633-nm beam was verified not to
erase the grating. The writing continued until the
maximum diffraction was achieved.
After the gratings were written, the crystal was
cooled to just above the transition, and the diffrac-
tion efficiency was determined as a function of ap-
plied field. The results are illustrated in Fig. 4.
The three curves shown are for gratings that were
written at +1450, 0, and -1450 V/cm. When the
grating was optically erased with the argon beams,
some residual diffraction (-1%o) remained that was
not optically erasable and could only be removed by
heating the crystal to room temperature.
The highest diffraction efficiency observed for
488-nm writing beams was 75% for a sample of
thickness 2.9 mm, where corrections were made for
Fresnel losses. For 514-nm writing beams, the
maximum value was reduced to 30%, and at 633 nm
the diffraction was almost undetectable. The writ-
(b)
. ' f \"In
k w-1| ... S~~~~ 488nm Ml
T.C.
110 120 130
Temperature (K)
BS
140 150
Fig. 2. (a) Dielectric constant of the KLTO.85 7No.12 9. The
phase transition is -50 K higher than in a comparable
KTN. (b) Dielectric constant of KTO.86NO.13.
Beer's law.1 2 We calculate [Cu"] = 6.0 X 10 19/cm3
and [Cu2"] = 2.1 X 10l8/cm3 .
White-light birefringence measurements between
crossed polarizers were used to measure the effec-
tive quadratic electro-optic coefficients. We deter-
mined gl - 912 = 0.186 m4 C -2 to an accuracy of 5%.
The dielectric constant was monitored as a func-
tion of temperature by measuring the capacitance of
the crystal, where C = eoeA/d. The results, shown
in Fig. 2(a), are compared with those obtained from
a KTN crystal with a similar tantalum:niobium ra-
tio [Fig. 2(b)]. The cubic/tetragonal transition tem-
perature has been raised approximately 60 K, to
178 K. The FWHM, i.e., the temperature range
over which the dielectric constant drops to half its
maximum value, is increased to -10 K. Diffraction
due to the linear electro-optic effect was weak di-
rectly below the transition and grew steadily as the
temperature was lowered, indicating a second-order
transition.
The diffraction experiments with applied field
were performed as in Fig. 3 with the sample main-
/t"u Ccum LjJ dbfected
cr ost -t detector
Fig. 3. Experimental setup for measurement of diffrac-
tion efficiency. Photorefractive crystal Xtl is mounted in
a vacuum cryostat. Beam splitter BS and mirrors
MI and M2 create a 488-nm grating that is read with
the Bragg-matched 633-nm beam and mirror M3. Dif-
fraction is measured versus applied voltage Vo. The tem-
perature was monitored by thermocouple T.C.
U
C
Ui
a
-2400 -1600 -800 0 800 1 600 2400
Applied Field, V/cm
Fig. 4. Two-beam diffraction efficiency for gratings
written at +1450, 0, and -1450 V/cm.
/ L
'l ..
.( (\N
0
100
0
C0
0
.2
M
May 15, 1992 / Vol. 17, No. 10 / OPTICS LETTERS 715
ing times for maximum diffraction roughly followed
Twrite - 6 s2 cm2 W - light intensity incident upon the
crystal.
From the calculated index modulation of nj =
8.5 X 10', we determine the space-charge field to
be E,, = 150 V/cm. Using the writing time of 180 s
at beam intensities adding up to 27.2 mW, we esti-
mate the sensitivity for this KLTN crystal to be
7.30 X 10-6 cm3 /J for an applied field of 1.6 kV/cm.
Following the procedure outlined above, the erase
time near T, was up to 2 orders of magnitude
greater than the write time at T, + 15 K.
KLTN was also observed to display weak diffrac-
tion without an applied field at as much as 120 K
above the phase transition. At room temperature
the diffraction efficiency in a 3-mm-thick sample
was 0.65%. The effect was strongest with focused
beams and weakened as progressively larger areas
of the sample were illuminated. However, the dif-
fraction efficiency measured with a given beam
geometry was independent of beam intensity over
several orders of magnitude.
In the diffraction experiments performed, an
index grating was generated as in relation (2).
Thus the diffraction efficiency in the crystal is a
strong function of the dielectric constant E. The
largest effects occur near the phase transition. In
KLTN the lithium raised the transition tempera-
ture 60 K over that of a KTN cyrstal with similar
niobium concentration so that the temperature of
maximum response was correspondingly raised. By
choosing the proper niobium and lithium concentra-
tion, it may be possible to raise T, to near room tem-
perature while retaining a second-order transition.
As reported, the diffraction due to the linear
electro-optic effect was weak directly below the
transition and grew steadily as the temperature was
lowered. The fact that the linear electro-optic coef-
ficients are known to be large in this class of mate-
rials indicates that there is little spontaneous
polarization at the transition. In other words, the
transition displays second-order behavior and is at
best -weakly displasive. This agrees with KTN
studies in which the phase transition is reported to
become first order only for niobium concentrations
exceeding 30%o.1o
In the experiments of diffraction with an applied
field, the data are seen to follow a sin2 behavior with
saturation (Fig. 4). This saturation is at least
partly due to nonlinear polarizability of the medium
at high field strengths.6 From the data it is clear
that a compensating dc field of approximately
300 V/cm is induced in the crystal under the influ-
ence of the writing field. As described previously,
residual diffraction persisted when the gratings
were optically erased. Also the erase/write time
asymmetry was increased by up to 2 orders of mag-
nitude. The asymmetry in the erasure time close to
the transition may be due to the following mecha-
nism: It is well known that in these crystals dipo-
lar clusters are formed around impurities that move
outside the center of inversion. In the vicinity of
the phase transition the correlation length of these
clusters becomes large and their relaxation time in-
creases. Thus it is possible that a secondary grat-
ing is formed by these dipolar clusters in addition to
the normal space-charge grating. The erasure time
of the secondary grating is long in the vicinity of the
phase transition, and this causes the asymmetry.
This tentative explanation is currently under fur-
ther investigation. We hope to harness this effect
in the future to perform fixing in these materials.
In the experiments without an applied field, it was
observed that substantial diffraction only occurs
when the writing beams interfere over a small (uni-
formly strained) region of the crystal. We have
determined that the effect arises from a weak semi-
uniform strain that is due to the growth process.
In conclusion, we have demonstrated the growth
of a new photorefractive material, KLTN, and have
characterized its photorefractive properties.
Strong quadratic electro-optic coefficients, high dif-
fraction efficiences, and sensitivities of 7.30 x
10-6 cm3/J at 1.6 kV/cm were observed. Based on
this research, KLTN crystals seem to be highly
promising materials for volume hologram storage
applications. In addition, the aspect of voltage con-
trol leads naturally to various interconnect schemes
for neural networks.
This research is supported by the U.S. Army
Research Office.
References
1. P. J. Van Heerden, Appl. Opt. 2, 393 (1963).
2. D. Gabor, IBM J. Res. Dev. 13, 156 (1969).
3 D. Von der Linde and A. M. Glass, Appl. Phys. 8, 85
(1975).
4. Y Yacoby and A. Linz, Phys. Rev. B 9, 2723 (1974).
5. J. J. Van der Klink and D. Rytz, J. Cryst. Growth 56,
673 (1982).
6. A. Agranat, V Leyva, and A. Yariv, Opt. Lett. 14, 1017
(1989).
7. R. Orlowski, L. A. Boatner, and E. Kraetzig, Opt.
Commun. 35, 45 (1980).
8. K. Sayano, Accuwave, Santa Monica, Calif. 90404
(personal communication, 1990).
9. R. L. Prater, L. L. Chase, and L. A. Boatner, Phys.
Rev. B 23, 5904 (1981).
10. C. M. Perry, R. R. Hayes, and N. E. Tornberg, in Pro-
ceedings of the International Conference on Light
Scattering in Solids, M. Balkansky, ed. (Wiley, New
York, 1975), p. 812.
11. A. Agranat, K. Sayano, and A. Yariv, in Digest of
Meeting on Photorefractive Materials, Effects, and
Devices (Optical Society of America, Washington,
D.C., 1987), paper PD-1.
12. V Leyva, Ph.D. dissertation (California Institute of
Technology, Pasadena, Calif., 1991).


Accuwave,

Tornberg,

https://authors.library.caltech.edu/2884/1/AGRol92.pdf

Characterization of a new photorefractive material: Kl-yLyT1-xNx

Abstract

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Caltech Authors - Main