25-09-2012, 12:45 PM
Pyroelectrically induced photorefractive effect in Sro.61 Bao.39Nb2O6 :Ce
[attachment=34540]
Strontium barium niobate (Sr ,xBaNb 2O6; SBN)
mixed crystals show transitions into a ferroelectric
phase1 2 and large linear electro-optic coefficients. 3
Since the transition temperature from the ferroelectric
tetragonal phase into the paraelectric phase
depends on X, 4 tailoring of the nonlinear optical
properties is possible. SBN crystals exhibit high
photorefractive sensitivities,5 permitting many applications,
eg., optical data storage6' 7 and optical
data processing.8 For fast photorefractive effects
to be reached, large light intensities obtained from
Q-switched or mode-locked lasers are appropriate.
However, until now only a few investigations
of SBN at high light intensities have been performed.
Monson et al.9 reported on large self-pumped phaseconjugate
reflectivities of nanosecond pulses in SBN.
In 1988 Krumins et al.'0 investigated thermal holograms
in SBN crystals. Holograms were written
with Q-switched light pulses emitted by a Nd:YAG
laser and read with a continuous-wave laser. They
reported on transient gratings and deduced from the
relaxation speed the thermal conductivity of SBN. Recently
we discovered" " 2 that in ferroelectric crystals
at pulse laser intensities a new powerful photorefractive
mechanism appears.
Holographic writing with two intersecting pulses
(duration 15 ns) generates a phase grating. The
development of the refractive-index amplitude An
is shown in Fig. 1. The measured refractive-index
change for ordinarily polarized readout light exhibits
no pronounced transient contribution, and for a certain
light intensity the value is approximately six
times smaller than the stable refractive-index change
for readout light of extraordinary polarization. For
extraordinarily polarized readout light we observe
that during pulse illumination the refractive-index
change An reaches a certain value, which decreases
thereafter monoexponentially in the dark until Ansc
is reached. This value remains stable for as much as
1 ms.
[attachment=34540]
Strontium barium niobate (Sr ,xBaNb 2O6; SBN)
mixed crystals show transitions into a ferroelectric
phase1 2 and large linear electro-optic coefficients. 3
Since the transition temperature from the ferroelectric
tetragonal phase into the paraelectric phase
depends on X, 4 tailoring of the nonlinear optical
properties is possible. SBN crystals exhibit high
photorefractive sensitivities,5 permitting many applications,
eg., optical data storage6' 7 and optical
data processing.8 For fast photorefractive effects
to be reached, large light intensities obtained from
Q-switched or mode-locked lasers are appropriate.
However, until now only a few investigations
of SBN at high light intensities have been performed.
Monson et al.9 reported on large self-pumped phaseconjugate
reflectivities of nanosecond pulses in SBN.
In 1988 Krumins et al.'0 investigated thermal holograms
in SBN crystals. Holograms were written
with Q-switched light pulses emitted by a Nd:YAG
laser and read with a continuous-wave laser. They
reported on transient gratings and deduced from the
relaxation speed the thermal conductivity of SBN. Recently
we discovered" " 2 that in ferroelectric crystals
at pulse laser intensities a new powerful photorefractive
mechanism appears.
Holographic writing with two intersecting pulses
(duration 15 ns) generates a phase grating. The
development of the refractive-index amplitude An
is shown in Fig. 1. The measured refractive-index
change for ordinarily polarized readout light exhibits
no pronounced transient contribution, and for a certain
light intensity the value is approximately six
times smaller than the stable refractive-index change
for readout light of extraordinary polarization. For
extraordinarily polarized readout light we observe
that during pulse illumination the refractive-index
change An reaches a certain value, which decreases
thereafter monoexponentially in the dark until Ansc
is reached. This value remains stable for as much as
1 ms.