Showing papers on "Organic photorefractive materials published in 1994"

A photorefractive polymer with high optical gain and diffraction efficiency near 100

Abstract: PHOTOREFRACTIVE materials are of considerable interest for the development of all-optical devices1. The photoref ractive effect appears in materials that exhibit an electric-field-dependent refractive index and that are photosensitive, such that the spatial distribution of photogenerated charge carriers is modified on irradiation with light. The diffraction pattern formed by the interference of two coherent light beams within such a material generates a non-uniform internal electric field that in turn modulates the refractive index. The resulting refractive-index pattern forms a grating that can diffract light and thereby give rise to two-beam coupling, whereby one of the writing beams gains energy at the expense of the other—a property that can be exploited in photonic devices. Although the best photorefractive materials currently available are inorganic crystals such as LiNbO3, there is considerable interest in the development of photorefractive polymers2–8, owing to their structural flexibility, ease of processing and lower cost. We describe here a polymer composite with excellent photorefractive properties. We have achieved a diffraction efficiency approaching 100% and a net two-beam coupling gain of more than 200 cm–1, making these polymeric materials suitable for immediate application in areas such as dynamic holographic storage and optical information processing1.

Orientationally enhanced photorefractive effect in polymers

Abstract: We present experimental data that show that the greatly improved performance of a new class of photorefractive polymers [see Donckers , Opt. Lett.18, 1044 ( 1993)] is too large to be explained by the simple electro-optic photorefractive effect alone. In these materials a photoconducting polymer host is doped with a small concentration of a sensitizer and a large concentration of a nonlinear optical chromophore that has orientational mobility at ambient temperatures. We present a theoretical model for a new orientational enhancement mechanism in which both the birefringence of the sample and the electro-optic coefficient are periodically modulated by the space-charge field itself. The predictions of this model for the size of the enhancement (which is greater than an order of magnitude in diffraction efficiency), the polarization anisotropy between p-polarized and s-polarized readout, and the presence of index modulation at twice the grating wave vector are in good agreement with the measured properties. This orientational enhancement mechanism should be important in any system in which the nonlinear optical chromophores have sufficient orientational mobility and dipole moment so as to be oriented by the space-charge field itself.

Diffraction from optically written persistent plasma gratings in doped compound semiconductors

Abstract: We propose and demonstrate a new type of optical nonlinearity based on the properties of the DX center in doped compound semiconductors. We report measurements on samples of AlGaAs:Si which were exposed to interfering laser beams and find diffraction from a large, persistent refractive index change associated with the well‐known persistent photoconductivity effect in this material. The new effect is shown to exhibit a refractive index change 30 times larger than that of conventional photorefractive materials. We explain the origin of the refractive index change in terms of the plasma effect and show that its expected magnitude is consistent with our observations.

Photorefractive phase shift induced by hot-electron transport: multiple-quantum-well structures

Abstract: The photorefractive transport models that include hot-electron transport nonlinearities in the photorefractive transport equations introduce a new phase-shift mechanism that explains the large energy exchange recently observed in semi-insulating multiple-quantum-well structures during photorefractive beam coupling. We show that carrier heating by large applied electric fields contributes a nonlinear transport length that limits the magnitude of the space-charge electric field and introduces a photorefractive phase shift that can approach π/2. The nonlinear contribution is dependent on field strength and on fringe spacing and should be a general property of velocity saturation in the direct-gap semiconductors. These results may force a reinterpretation of apparent trap-limited behavior in bulk photorefractive semiconductors even under nonresonant excitation.

Fast Photorefractive effect in PVK:C60:DEANST Polymer Composite

Abstract: The photorefractive effect is observed and described in a polymeric composite consisting of poly[N-vinylcarbazole] charge transporting matrix, fullerene C{sub 60} photosensitizing molecules, and second-order active molecules of (diethylamino)nitrostyrene. The results of photoconductivity, electrooptic modulation, degenerate four-wave mixing, and two-beam coupling experiments are reported. The composite shows relatively high field-dependent electrooptic coefficient and charge carrier photogeneration quantum efficiency. The observed photorefractive diffraction efficiencies compare well with those of well-known inorganic materials. Time-dependent measurements reveal very fast kinetics of light induced phase grating formation and erasure. A possibility of efficient switching of the photorefractive effect with an external electric field is shown. 25 refs., 10 figs.

Optical properties of poly(N-vinylcarbazole)-based guest-host photorefractive polymer systems.

Abstract: The photorefractive properties of poly(N-vinylcarbazole) doped with a variety of nonlinear optical chromophores and sensitizing agents are surveyed. Steady-state diffraction efficiencies of greater than 10−3 and two-beam coupling gain exceeding the absorption loss are found in six materials combinations. The effect of the structure of the nonlinear optical chromophore on the photorefractive properties is discussed.

Enhanced photorefractive performance in a photorefractive polymeric composite

Abstract: We characterize the photorefractive behavior of a photorefractive multicomponent polymer composite of PVK‐TCP:C60:DEANST. Efficient plasticization of the host polymeric matrix and utilization of a nonlinear chromophore with a large dipole moment provide a large poling‐induced electro‐optic coefficient. Diffraction efficiencies as high as 40% and asymmetric net two‐beam coupling gain coefficients in excess of 130 cm−1, surpassing those of known inorganic single‐crystalline photorefractive media, are reported.

Photorefractive Effect in a Polymer Molecularly Doped with Low-Molecular-Weight Compounds

Abstract: The photorefractive effect is observed in poly (methylmethacrylate) molecularly doped with three types of low-molecular-weight compounds, carrier transport (CTM), carrier generation (CGM) and nonlinear optical (NLO) materials. With these materials as dopants, the polymer exhibits both photoconductivity and the electro-optic (EO) effect under DC electric fields. The EO coefficient r33 is found to be linearly dependent on applied fields because of the lower glass-transition temperature (T g). In two-beam coupling and diffraction measurements, refraction gratings are written in the polymer. A phase shift of 90° between a refraction grating and a fringe pattern with applied fields proves the existence of the photorefractive effect, which is distinguished from heating effects. A maximum diffraction efficiency η of 4×10-6 is obtained in the photorefractive polymers.

The role of absorbing nonlinear optical chromophores in photorefractive polymers

Abstract: Organic photorefractive materials have only recently been considered as alternatives to inorganic crystals such as lithium niobate, despite the fact that they offer possible advantages, such as mechanical flexibility, low fabrication costs, and the ability to chemically tune the properties of the material. The influence of the nonlinear optical chromophore on various phenomena observed in a photorefractive polymer is reported on the basis of a study of samples derived from poly(N-vinylcarbazole) sensitized with 2,4,7-trinitro-9-fluorenone.

Recent progress in photorefractive polymers: materials and structures

Abstract: A new class of photorefractive polymers is described in which an inert polymer binder is doped with a great molecule called a dual-function dopant, which has the dual functions of providing optical nonlinearity as well as charge transport as required for the photorefractive effect. These materials are the first photorefractive polymers to show both nondestructive readout as sufficiently low reading power and optical trap activation, in which pre-irradiation by a uniform light beam increases the concentration of deep trapping sites in the material. In the area of potential applications, a new sample configuration is described in which photorefractive polymers are fabricated into an electric field switchable stratified volume holographic structure. Individual layers may be activated by applied electric field leading to improved diffraction efficiency and angular selectivity.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photorefractive gratings in planar optical waveguides in cubic crystals

Abstract: The space-charge field of the photorefractive grating in planar waveguides in cubic crystals is considered. Analytical expressions are derived from three cases: the initial stage of photorefractive grating formation, the steady state, and the photorefractive grating formation in waveguides with a short diffusion length and high dark conductivity and without trap saturation. The orientation dependencies of the waveguiding two-beam coupling factor for the (110), the (111), and the (100) cuts of the substrate are considered. The overlap factors of the cross distributions of the space-charge field and the light field of the waveguide modes are calculated for waveguides with a step-shaped profile of the refractive index.

Photorefractive self-focusing and defocusing as an optical limiter

Abstract: Focusing and defocusing of laser light has been observed for many years. Kerr type materials exhibit this effect but only for high intensities. We show experimental evidence that photorefractive materials can also produce dramatic focusing and defocusing. Whereas Kerr materials produce this effect for high intensities, photorefractive materials produce these effects independent of intensity indicating that this effect would be ideal for an optical limiter. We compare the characteristics of Kerr and photorefractive materials, discuss the physical models for both materials and present experimental evidence for photorefractive defocusing. Self-focusing and defocusing was observed for any incident polarization although the effect was more pronounced using extraordinary polarized light. In addition, self-focusing or defocusing could be observed depending on the direction of the applied electric field. When the applied field was in the same direction as the crystal spontaneous polarization, focusing was observed. When the applied field was opposite the material spontaneous polarization, the incident laser light was dramatically defocused.

Shallow trap modelling of infrared sensitive BaTiO/sub 3/

Abstract: We present experimental data for the intensity-dependent absorption coefficient of a photorefractive "blue" sample of rhodium-doped BaTiO3 using beams of different wavelengths. A numerical photorefractive two-level model incorporating dual-wavelength illumination and a secondary photorefractive centre gives good agreement with experiment. We deduce values for the number densities, photoionisation cross-sections, thermal ionisation rate and recombination coefficients of the photorefractive centres. In this sample we determine that there is the usual deep trap concentration of ~ 2x10.

Photorefractive grating development with parametric interactions at radiation mode pump in lithium niobate optical waveguides

Abstract: Four - wave photorefractive parametric interactions in lithium niobate planar optical waveguides withadvanced photorefractive sensitivity have been observed and experimentally studied. Photorefractive gratings of arbitral3r periOds at using the extraordinaiy radiation mode as a pump have been obtained in such interactions. 1. INTRODUCTIONThe photorefractive effect that is the refractive index change via the light influence is observed in many electrooptical crystals and optical waveguides on their ground. Such changes replicate the light intensity patterns andform phase dynamic holograms -socalled "photorefractive gratings" 1,2 These gratings are of great interest in order to provide optically controlled switching and interconnections for associative optical memory devices , neural nets and optical processors including their integrated -opticalrealizations ". It is well known that photorefractive properties of most electrooptic crystals as well as corresponding optical waveguides considerably depend on the presence and

Polymeric composite photorefractive materials for nonlinear optical applications

Abstract: Polymeric composite materials constitute a new and very promising class of photorefractive materials. In the design of polymeric photorefractive materials we use multicomponent composites in which necessary functionalities can be independently optimized. The investigated composites consisted of charge transporting polymeric matrix, and optically second-order active molecules. Two different photosensitizers were used to vary the wavelength response. Photorefractive properties of these materials were investigated using erasable volume holography in a non-degenerate four-wave mixing geometry and two-beam coupling techniques. A previously developed model of space-charge field grating formation in photoconductive polymers was used to explain the field dependence of four-wave mixing diffraction efficiency. The model takes into account the field dependence of charge photogeneration quantum yield, carrier field mobility, and electro-optic coefficient. Necessary information about these parameters was obtained from the results of photoconductivity and electro-optic modulation experiments. Special attention was focused on the kinetics of photorefractive response in the composite for optical signal processing and optical storage. It was found that a very effective switching of diffraction efficiency induced by dc electric field occurs in this system. Also, the results of kinetic studies of the index grating writing and its subsequent light-induced erasure, as well as a demonstration of the holographic image recording and retrieval, are reported.

A new class of strongly photorefractive materials

Abstract: Certain doped compound semiconductors exhibit persistent photoconductivity (PPC) at low temperatures as a result of the optical ionization of electrons from deep, spatially localized, donor levels known as DX centers We calculate that this release of carriers also produces a refractive index shift (through the plasma effect) which is 30 times larger than that of conventional photorefractive materials, We report the results of diffraction measurements on samples of AlGaAs which support this prediction The induced index changes can be erased by heating above an annealing temperature determined by the material composition >

Photoconducting polymers for photorefractive nonlinear optics

Abstract: Photoconducting polymers doped with nonlinear optical molecules show important photorefractive properties. These new polymer composites are promising materials for photonic applications such as dynamic holographic storage and image processing. The photorefractive properties of a highly efficient polymer composite based on poly(N-vinylcarbazole) are investigated and discussed.

Fanning effect and phase conjugation in Bi/sub 12/TiO/sub 20/ photorefractive fiber

Abstract: Study of photorefractive phase conjugate mirror is of great importance on account of various practical applications, such as optical implementation of neural network, associative memories, synchronization of several isolated lasers, interferometry, etc. A double phase conjugate mirror (DPCM) offers more advantages because no coherence between laser pump beams is needed. BSO-type crystals represent an important class of photorefractive materials due to their fast response time.’ Fiber-like samples have several advantages compared to the bulk crystal.’ We present here an experimental investigation of the double phase conjugation and of the fanning effect in fiberlike photorefractive Bi,,TiO,, (BTO) crystal supplied by alternating electric field of square-wave form at the wavelength of He-Ne laser (X = 632.8 nm). It was found that features of photorefraction in fiberlike samples are quite different with bulk crystals. It is known3 that the fanning effect (strong enhancement of scattered light) in photorefractive crystals is fundamental for the DPCM recording. An angular distribution of scattered light emerging from the BTO fiber is rather complicated owing to the influence of internal reflections from the longer fiber faces. However, it is possible to find several bands of the pump beam’s incidence angle when the fanning light is concentrated around a direction, from which the second pump in its turn could produce fanning light in the counter-direction of the first pump (see Fig. 1). This condition is favourable to record an effective DPCM by using two mutually incoherent pump beams? Experiments were carried out with BTO photorefractive fibers having a length of 10-15 mm and a cross section of about 1 mm. It was observed that the DPCM in the BTO fiber possesses a much higher phase conjugate reflectivity than in BTO bulk crystal. We got the phase conjugate reflectivity up to 18% in the BTO fiber without antireflected coating at the wavelength of the He-Ne laser (A = 632.8 nm). Obtained reflectivity is the highest anyone ever got in this type of crystal. The behaviour of the phase conjugate wave in the fiber was observed to be different from that in the bulk crystal.

Selective light-induced scattering in photorefractive crystals

Abstract: tric crystals of barium sodium niobate (NBS), yttrium-doped lithium niobate (LN), and KHJ' O, (KDP) were studied. Due to the crystal growth conditions the layer-type domains formed a periodic two-dimensional superlattice in NBS and NL. In the case of KDP the domain subsystem consisted of domain blocks with quasiperiodic structure. The frequencyangular intensity distribution of polarized scattered light was registered at small angles (0-10') relatively to the pump direction. This technique allows to study polariton dispersion in Raman spectra.' pump radiation being of laser type. Elastic scattering spectra were obtained with a source of polarised radiation of wide spectral range. It was found that two diffraction effects must be taken into account in the processing of Raman spectra from multiply domained crystals. The first one is the linear diffraction of pump and scattered radiation. Under proper conditions additional branches or parts of them appear in spectra. In the case of KDP the ansiotropic diffraction of light leads to the appearance of gaps in the intensity distribution on the polariton branches, to the violation of the selection rules. The explanation of such spectra behaviour comes from the elastic scattering spectra, consisting of a large number of narrow lines with the same frequency-angular divergence as that of the gaps in Raman spectra. The second one is nonlinear diffraction due to the periodic variation of nonlinear susceptibility of a multiply domained crystal. The variation of secondorder optical properties between two neighbouring domains can be significantly higher than that of the first-order properties. In case of LN and the NBS the polar axes of the neighbouring domains were oriented oppositely and the sign of the quadratic susceptibility changed at the boundary. All diffraction effects lead to the appearance of the same shifted curves in spectra. The shift is determined by the relation

Optical and electron paramagnetic resonance investigation of the role of vanadium in photorefractive CdTe:V

Abstract: Cadmium telluride has been regarded as a material of choice for many envisioned photorefractive applications in the infrared because of its high electrooptic coefficient. We recently demonstrated high beam-coupling gains in CdTe:V using applied electric fields. The prospects of using this gain enhancement mechanism in self-pumped phase conjugators and the experimental demonstration of the theoretically predicted high sensitivity of the photorefractive process in CdTe:V has attracted more attention towards the development and the optimization of the photorefractive properties of this materia1. Experience has shown that vanadium is a proper dopant that results in both high resistivity and efficient photoconductive and photorefractive responses over a wide wavelength range in the infrared. Further development of this material requires an understanding of the role of V in the photorefractive process. We report on photorefractive characterization, optical absorption, photoluminescence and electron paramagnetic resonance of vanadium-doped CdTe. The results of these experiments outline the role of vanadium in the photorefractive process. >

Transient two-wave mixing of photorefractive Bi/sub 12/SiO/sub 20/ crystal with a square a.c. electric field

Abstract: Two wave mixing (TWM) gain in photorefractive materials is one of the most fundamental and attractive aspects of the photorefractive effect. Several techniques for the enhancement of TWM gain have been developed and analysed by many researchers. In this paper we developed the corresponding theory describing the buildup of the space-charge field in the presence of square a.c. field and compared with the experimental results of the full temporal variation of the TWM gain for the square applied fields in a photorefractive Bi/sub 12/SiO/sub 20/ crystal. >

Effect of holographic storage of information in photorefractive waveguides

Abstract: The paper presents a study of a single-mode Ti and Fe in-diffusion waveguide. We have reported in this letter the experimental observation of diffraction effects due to the formation of a transitory photorefractive grating. The interference of a guided-wave with light scattering inside the waveguide can form a spatial phase grating due to the photorefractive effect, analogous to the storage process of holograms in bulk crystals. The storage mechanism in these materials is based on light induced permanent changes of the refractive index--the photorefractive effect. In this paper some advantages and limitations of this method are discussed.

Observation of misalignment of the subharmonic grating in photorefractive Bi/sub 12/SiO/sub 20/

Abstract: but only in the limit of small modulation. In practice, most experimental conditions cannot be adequately described by the linearized theory. The correction function used by Refregier et al.' describes the effect of modulation, but only for twowave mixing at the optimum velocity. Au and Solyma? have demonstrated numerically a complicated photorefractive response. In this paper we provide more detailed numerical analysis, and for the first time, experimental characterization of the photorefractive response, including both diffraction and energy transfer, in BSO as function of modulation index and fringe velocity. A finite difference technique was used to model the photorefractive grating formations. This approach calculated the full space charge field within the resolution of the element size, providing spatial and temporal evolution of the space charge field up to modulation m = 1. The experimental arrangement utilized an argon-ion or a double Nd:YAG laser to write the holograms. A HeNe laser was used in the non-degenerate four-wave mixing configuration to measure the diffraction efficiency. At large modulation the space charge field characteristics exhibited a complicated dependence on the fringe velocity, as demonstrated for the case of m = 0.9 in Fig. 1, where the calculated amplitude, phase, and imaginary part of the fundamental component of the space charge field are plotted versus normalized velocity. Here vOpt is the resonant velocity at small modulation. Experimental results are shown in Fig. 2, which compare the measured two-beam coupling gain and diffraction efficiency as a function of fringe detuning. The optimum frequency at small modulation was 2.4 Hz. The fringe velocity that optimized the diffraction efficiency depended strongly on modulation index, particularly at very large modulation, and was not always the same as the optimum velocity for energy transfer. In general, the optimum velocity for diffraction increased with increasing modulation, but at very large modulation shifted to very small fringe velocities. This effect is demonstrated in Fig. 3. , The numerical results predict the saturation in the two-wave mixing associc ._ ?. 0.6 1

Nonlinear photorefractive effects in liquid crystals

Abstract: In this paper, we present the first observation, to our knowledge, of orientational photorefractive [OPR] effects in nematic liquid crystal film. The effect is attributed to molecular axis reorientation caused by the combination of an applied dc field and the dc space charge field induced by the impinging optical field. The refractive index change is a Kerr-like phenomena, and is quadratically defendant on the electric field strength present, unlike the usual [linear] photorefractive effect. To generate such orientational photorefractive effect in aligned nematic liquid crystal films, the applied dc field strengths are on the order of 100 V/cm.

Influence of pyroelectric fields on the photorefractive effect

Abstract: tored as a function of the intensity of a second, near infrared beam from the Ti: sapphire laser. The infrared beam was also o-polarised so as to minimise photorefractive grating effects. The graph in Fig. 3 shows an increase in the apparent HeNe absorption of up to -0.2 cm-’ when the crystal is exposed to the infrared radiation. The solid curve shows the theoretical curve using, once again, parameters derived from the experimental points using the shallow trap rate equations. Further results demonstrating photoinduced absorption effects at argon ion laser wavelengths will also be presented. *Imperial College of Science, Technology and Medicine, The Blackett Laborato ry, Prince Consort Road, London SW7 2BZ, U.K. T a n d o z Huningue S. A., Centre de Recherche en Optoblectronique, Avenue de BdIe, 68330 Huningue, France 1. S. MacCormack, J. Feinburg, M. H. Garrett, CLEO Technical Digest 11, CThS55 (1993). G. W. Ross, P. Hribek, R. W. Eason, M. H. Garrett, D. Rytz, Opt. Commun. 101, 60 (1993). B. A. Wechsler, M. B. Klein, C. C. Nelson, R. N. Schwartz, “Spectroscopic and photorefractive properties of infrared sensitive rhodiumdoped barium titanate,” Optics Letters, in press. 4. P. Tayebati, D. Mahgerefteh, J. Opt. Soc. Am. B 8, 1053 (1991). 5. G. A. Brost, R. A. Motes, Opt. Lett. 15, 538 (1990). 2.

Photorefractive and SBS backscattering-a comparison

Abstract: sample A was used and s-polarized when sample B was used. Two Peltier coolers controlled the sample temperature. The absorption coefficient at 1.06 IJ-m was 2.8 cm-' for sample A and 2.2 cm-' for sample B. The two-wave mixing gain coefficient r in the sample B was measured to be 7 cm-' at an applied electric field of 12 kV/cm and a pump to signal beam ratio of 400. Due to the large light-induced refractive index change the laser beam passing through the photorefractive sample gave rise to a broad-angle fan of amplified stray light.' The transversal intensity distributions detected by the diode array or the CCD-camera show that the intensity distribution of the fanning beams takes a bell shape with the maximum nearly symmetric to the incident beam with respect to the sample surface normal. The displacement of the intensity maximum depends on the crystal and experimental symmetry. A photorefractive oscillator involves the self-buildup of the grating and formation of the new light beams. We used two mirrors to feed back a part of the fanning beams from the sample B to contribute the generation of one grating and the wash-out of the others in the crystal. After a short response time a new laser beam was obtained from the oscillator as shown in Fig. 2: The oscilloscope trace at the bottom is the intensity of the pump beam in front of the crystal. The upper trace is that behind the crystal. The middle one is the intensity of the new beam from the oscillator detected behind the beam splitter BS. We see, if we turn on the pump beam, a new laser beam was generated with a time constant of about 70 ms, which is determined by the material response and the self-organization of gratings. Due to the fanning and energy transfer to the oscillator the pump beam with an intensity of 23 mW/cm2 was depleted up to 60%. To evaluate the energy transfer efficiency from the pump beam to the oscillator we measured the intensity of the oscillating beam outside the oscillator and derived the intensity inside with the help of the reflectivity of the beam splitter. This leads to an energy transfer efficiency of 55%. 1. J. E. Millerd, E. M. Garmire, M. B. Klein, Opt. Lett. 17, 100 (1992). 2. J. Feinberg: J. Opt. Soc. Am. 72, 4652 (1982). CTuH3 (Invited) 1130

Influence of modulation and fringe velocity on the photorefractive response with moving gratings in Bi/sub 12/SiO/sub 20/

Abstract: sample A was used and s-polarized when sample B was used. Two Peltier coolers controlled the sample temperature. The absorption coefficient at 1.06 IJ-m was 2.8 cm-' for sample A and 2.2 cm-' for sample B. The two-wave mixing gain coefficient r in the sample B was measured to be 7 cm-' at an applied electric field of 12 kV/cm and a pump to signal beam ratio of 400. Due to the large light-induced refractive index change the laser beam passing through the photorefractive sample gave rise to a broad-angle fan of amplified stray light.' The transversal intensity distributions detected by the diode array or the CCD-camera show that the intensity distribution of the fanning beams takes a bell shape with the maximum nearly symmetric to the incident beam with respect to the sample surface normal. The displacement of the intensity maximum depends on the crystal and experimental symmetry. A photorefractive oscillator involves the self-buildup of the grating and formation of the new light beams. We used two mirrors to feed back a part of the fanning beams from the sample B to contribute the generation of one grating and the wash-out of the others in the crystal. After a short response time a new laser beam was obtained from the oscillator as shown in Fig. 2: The oscilloscope trace at the bottom is the intensity of the pump beam in front of the crystal. The upper trace is that behind the crystal. The middle one is the intensity of the new beam from the oscillator detected behind the beam splitter BS. We see, if we turn on the pump beam, a new laser beam was generated with a time constant of about 70 ms, which is determined by the material response and the self-organization of gratings. Due to the fanning and energy transfer to the oscillator the pump beam with an intensity of 23 mW/cm2 was depleted up to 60%. To evaluate the energy transfer efficiency from the pump beam to the oscillator we measured the intensity of the oscillating beam outside the oscillator and derived the intensity inside with the help of the reflectivity of the beam splitter. This leads to an energy transfer efficiency of 55%. 1. J. E. Millerd, E. M. Garmire, M. B. Klein, Opt. Lett. 17, 100 (1992). 2. J. Feinberg: J. Opt. Soc. Am. 72, 4652 (1982). CTuH3 (Invited) 1130