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1.
Study of transient photorefractive beam coupling in high- and low-molar-mass liquid crystal mixtures
We observed transient signals of Bragg grating formation in high-performance photorefractive high- and low-molar-mass liquid
crystal mixtures (HL-LCMs). These transient signals including oscillation-like behavior can be explained by a complex time
constant in the case of a finite applied dc field. The time constant for the space-charge field to reach its steady state
and the oscillation frequency are estimated.
Received: 30 October 1998 / Revised version: 14 December 1998 / Published online: 24 February 1999 相似文献
2.
G. Cedilnik M. Esselbach A. Kiessling R. Kowarschik E. Nippolainen A.A. Kamshilin V.V. Prokofiev 《Applied physics. B, Lasers and optics》1999,68(5):983-987
In a photorefractive Bi12SiO20 crystal with high applied electric ac field of square-wave shape a fast two-wave coupling response (less than 1 s) and a
slow hologram readout decay (minutes) was found for a wavelength of 633 nm. This can be explained by electron–hole transport
with two trap levels. An intensity dependence of the slower complementary grating was found. Illuminating with the readout
wave without applied electric field leads to a very slow grating decay (many hours).
Received: 18 November 1998 / Revised version: 3 February 1999 / Published online: 7 April 1999 相似文献
3.
L. Frey G. Pauliat J.M. Jonathan M. Dumont G. Roosen 《Applied physics. B, Lasers and optics》1999,68(5):999-1005
From thermodynamic considerations, we derive a consistent set of equations coupling the steady-state photoinduced photorefractive
space-charge field to mechanical deformations, dc permittivity, and refractive index changes. For the first time to our knowledge,
these equations include piezoelectricity, electrostriction, the elasto-optic effect, the linear and quadratic electro-optic
effects, as well as the influence of the volume forces and electric torques. We determine the conditions on the material parameters,
for which volume forces and torques are of some importance on the optical properties.
These equations resulting from a macroscopic approach are valid whatever the physical microscopic origins of the various effects.
Non centrosymmetrical and centrosymmetrical materials are considered. The order of approximation is the lowest possible able
to describe the mentioned effects in both types of materials.
Received: 18 November 1998 / Revised version: 18 February 1999 / Published online: 12 April 1999 相似文献
4.
A. Thompson N. Nazhestkina A. Siahmakoun G. Duree N. Roesler 《Applied physics. B, Lasers and optics》2003,76(5):547-554
We present experimental investigations of electrical fixing techniques in Ce:SBN:60. The effect of crystal fatigue on the
diffraction efficiency of electrically fixed photorefractive gratings is studied. We observed that applying an ac field to
the crystal eliminated crystal fatigue and improved diffraction efficiency. A controllable diffraction efficiency of a photorefractive
grating is presented. A reproducible diffraction efficiency of up to 75% is obtained using a write-reveal grating technique
with high-voltage pulses of opposite polarity. We also show that the diffraction efficiency can be controlled by varying the
intensity of the writing beams incident to the crystal during the recording process. A method of determining the hysteresis
loop using the domain-fixing technique is proposed. The dependence of the diffraction efficiency on the direction of the applied
electric field while writing the hologram is studied. Our experiments show that, during writing, when the electric field is
applied opposite to the c axis the grating can be successfully revealed with both positive and negative dc voltages. However,
when the grating is written with a field parallel to the c axis, the grating can be revealed only with a field applied in
the opposite direction.
Received: 28 October 2002 / Revised version: 28 February 2003 / Published online: 14 May 2003
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ID="*"Corresponding author. Fax: +1-812/872-6167, E-mail: azad.siahmakoun@rose-hulman.edu 相似文献
5.
S.M. Shandarov N.I. Nazhestkina O.V. Kobozev A.A. Kamshilin 《Applied physics. B, Lasers and optics》1999,68(5):1007-1012
The space-charge-field formation in a photorefractive crystal illuminated by a one-dimensional light pattern is studied when
an alternating square-wave electric field is applied to the crystal. We derive the general nonlinear equation for the time-averaged
distribution of the space-charge field and employ the simplified versions of this equation to analyze the space-charge-field
formation in the case of a Gaussian beam and interference light pattern. The borders of the applicability of simplified equations
and analytic expressions to describe a self-action of light beams and the large modulation effects under two-beam coupling
are estimated from the numerical calculations.
Received: 18 November 1998 / Revised version: 26 January 1999 / Published online: 12 April 1999 相似文献
6.
N.I. Nazhestkina A.A. Kamshilin O.V. Kobozev V.V. Prokofiev T. Jääskeläinen 《Applied physics. B, Lasers and optics》2001,72(6):767-773
Two-wave mixing of phase-modulated beams in photorefractive crystals under a dc electric field is studied both theoretically
and experimentally. Based on the vectorial theory of light diffraction in crystals of cubic symmetry, we derived an analytical
expression that describes the phase demodulation in crystals with an arbitrarily oriented electric field. The phase-demodulation
technique was used for estimation of the space-charge field created in photorefractive crystals. It is shown that the space-charge-field
grating created in GaP and Bi12TiO20 crystals is much smaller than that predicted from the one-level band-transport model of the photorefractive effect.
Received: 12 December 2000 / Revised version: 8 February 2001 / Published online: 27 April 2001 相似文献
7.
X.L. Lei H.L. Cui 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):513-518
We suggest a balance-equation approach to hot-electron transport in a single arbitrary energy band subject to an intense radiation
field of terahertz (THz) frequency, including all the multiphoton emission and absorption processes and taking account of
realistic scatterings due to impurities and phonons. This approach, which allows one to calculate THz-driving, time-averaging
transport based on a set of time-independent equations, provides a convenient method to study the effect of an intense THz
electric field on carrier transport in a nonparabolic energy band. As an example, these fully three-dimensional, acceleration-
and energy-balance equations are applied to the discussion of superlattice miniband transport at lattice temperature T=77 and 300 K driven by the THz radiation field of varying strengths. It is shown that the current through a dc biased miniband
superlattice is greatly reduced by the irradiation of an intense THz electric field.
Received: 23 January 1998 / Revised: 31 March 1998 / Accepted: 20 April 1998 相似文献
8.
Transmission behavior in a photorefractive polymer film 总被引:2,自引:0,他引:2
When a p-polarized beam propagates through a high-performance photorefractive polymer composite, poly dimethyl-4-(4′-nitrophenylazo)benzene, its transmission behavior is influenced by three effects: the electroabsorption, the photorefractive
coupling with the reflected beam from the rear surface, and the amplified scattering. From the measurements on the incidence
angle dependence as well as the applied-electric-field dependence of the three effects, some conclusions are obtained. At
a small incidence angle with a low applied electric field, both the amplified scattering and the electroabsorption are small
whereas the coupling between the incident beam and the reflected beam plays a principal role. At a large incidence angle or
with a high poling electric field, the transmission is influenced mainly by the amplified scattering and the electroabsorption.
A poling electric field asymmetric loss to the amplification scattering is also observed.
Received: 18 November 1998 / Revised version: 10 February 1999 / Published online: 12 April 1999 相似文献
9.
The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc electric field at different temperatures has been studied. In particular, the temperature dependence of the characteristic time constant has been studied both theoretically and experimentally, showing a strongly decreasing time constant with increasing temperature. 相似文献
10.
Liang Song 《Optics Communications》2006,259(1):293-297
We investigated the ring-pattern characteristic of self-phase modulation in a homeotropic nematic liquid crystal cell induced by a focused Ar-ion laser beam. Laser induced self-phase retardation versus incident angle was experimentally studied, and good agreement with theory was found. Effects of applied dc electric field on the ring-pattern were studied, to our knowledge, for the first time. When the electric field was below a critical value, laser induced self-phase retardation could be varied by changing the electric field strength. Above this value, irregular shaped diffraction pattern accompanied by intense light scattering was observed, which is attributable to honeycomb-like domain formation. 相似文献
11.
S. Schloter A. Schreiber M. Grasruck A. Leopold M. Kol’chenko J. Pan C. Hohle P. Strohriegl S.J. Zilker D. Haarer 《Applied physics. B, Lasers and optics》1999,68(5):899-906
We present a detailed study of the photoelectric as well as the holographic properties of a novel organic photorefractive
glass based on triphenylamine. We studied the quantum efficiency Φ of the photogeneration of charges by means of photoinduced
discharge measurements. The photoconductivity σ and the charge carrier mobility μ were obtained via dc photoconduction and
pulsed time-of-flight experiments, respectively. The holographic characterization was performed by two-wave and degenerate
four-wave mixing experiments allowing for the determination of properties such as diffraction efficiency η, modulation of
the refractive index Δn, gain coefficient Γ, and phase-shift φp of the investigated system. The experimental data for Φ could be successfully described by the Onsager formalism with a thermalization
radius of r0=24 ? and a primary quantum yield of Φ0=40%. We evaluated the E field and temperature-dependent measurements of μ using the B?ssler formalism yielding a width of
the density of states of σ=0.13 eV and a disorder parameter Σ=3.6. On this basis the lifetime and the average drift length
of the charge carriers could be estimated from the dc photoconduction experiments. From the photoelectric measurements we
also calculated the holographic response time that matched very well to the measured response time and described the E-field
dependence satisfactorily. The presented photorefractive system shows outstanding optical properties and stability with respect
to degradation. We measured a gain coefficient of Γ=90 cm-1, and a diffraction efficiency of η=27% at a response time of 30 ms for only 40-μm-thick samples. Orientational enhancement
was observed and evaluated quantitatively. To our knowledge, this work presents the first determination of each of the above
quantities all in one single organic photorefractive material.
Received: 16 November 1998 / Revised version: 4 January 1999 / Published online: 31 March 1999 相似文献
12.
F. Mougel F. Augé G. Aka A. Kahn-Harari D. Vivien F. Balembois P. Georges A. Brun 《Applied physics. B, Lasers and optics》1998,67(5):533-535
3+ :Ca4GdO(BO3)3 (Nd:GdCOB). 21 mW of green cw laser emission for an absorbed pump power of 820 mW were achieved under laser diode-pumping.
64 mW of green cw laser output were obtained with 1 W of absorbed pump power under titanium-sapphire pumping. Its availability
in large-size crystals with good optical quality makes Nd:GdCOB a true challenger to the best SFD laser crystal reported so
far: Nd:YAl3(BO3)4 (Nd:YAB or NYAB).
Received: 2 March 1998/Revised version: 20 May 1998 相似文献
13.
E. Plaut L. Pastur R. Ribotta 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):283-297
We study experimentally the evolution of thermoconvection in a laterally extended planar nematic layer, at zero or weak stabilizing
magnetic field. As the applied thermal gradient is increased, a cascade of symmetry breakings occurs, towards structures of
increasing spatial complexity, and ultimately towards oscillating states. The patterns are characterized optically, and simple
models for the distortion of the vertical (out of plane) component of the director field are proposed.
Received: 1st December 1997 / Revised: 25 May 1998 / Accepted: 2 June 1998 相似文献
14.
B.P. Antonyuk 《Optics Communications》2007,269(1):142-147
We show that strong incoherent broad band light causes positive feedback in response to a static electric field in random media: electric current flows in opposite to a voltage drop direction; static polarization is induced in opposition to an applied electric field. This type of the electron motion amplifies the external action revealing anti-Le-Chatelet behavior. The applied static electric field is amplified up to the domain of optical damage of a silica glass ≈107 V/cm. 相似文献
15.
The influence of an external field on photorefractive recording in Sn2P2S6 (SPS) crystals is studied. A large gain factor of more then 15 cm-1 is achieved for a grating spacing of 12 μm at λ=0.9 μm. For an applied field exceeding ±200 V/cm a switching of the beam
coupling direction is detected, exhibiting a pronounced hysteresis.
Received: 25 October 2000 / Revised version: 18 January 2001 / Published online: 21 March 2001 相似文献
16.
We report electro-optical effects in planar-aligned liquid-crystal cells of pristine and doped calamitics in the presence of dc voltage. The doped cells comprise both a nematic host and a minute amount of either buckminsterfullerene or multiwalled carbon nanotubes. The voltage–transmittance and voltage–capacitance hystereses were observed from the sample cells in the range of applied dc voltage up to 8 V. Experimental evidence indicates that a nanoscale carbon dopant can affect the behavior of a nematic in terms of ion-charge effects and that doping with nanotubes can effectively reduce the driving voltage. 相似文献
17.
F. Wang Z. Chen Z. Huang Q. Gong Y. Chen H. Chen 《Applied physics. B, Lasers and optics》1998,67(2):207-210
-1 and an index grating amplitude of about 4.3×10-3 were obtained. Furthermore, high solubility of the dye in PVK and high stability of the photorefractive composite were also
exhibited.
Received: 7 January 1998/Revised version: 7 April 1998 相似文献
18.
Probing photo-induced alignment in poly(vinyl cinnamate) films by surface second-harmonic generation
I. Drevenšek Olenik M.W. Kim A. Rastegar T. Rasing 《Applied physics. B, Lasers and optics》1999,68(3):599-603
Received: 20 September 1998 / Revised version: 18 December 1998 相似文献
19.
First experimental evidence for the existence of an electrooptic effect for cold neutrons in 7LiNbO3 is reported and discussed. The effect is based on the fact that in certain photorefractive crystals a light-induced space-charge
field can be generated which causes a modulation of the density via the inverse piezoelectric effect. From such density structures,
induced by the internal electric field, cold neutrons can be diffracted.
Received: 13 November 1998 / Revised version: 21 December 1998 / Published online: 12 April 1999 相似文献
20.
We present investigations of the etalon effect in sillenite photorefractive crystals with a pulsed frequency-doubled Nd:YAG
laser and show its influence on two- and four-wave mixing. In four-wave mixing the etalon effect allows changes of the diffraction
efficiency by more than 80%. Results are supported by theoretical considerations.
Received: 15 April 1998/Revised version: 19 June 1998 相似文献