Terbium gallium garnet is an interesting representative of the family of rare-earth garnets. In these crystal we have observed a photorefractive effect. This effect is probably linked to the light-induced dichroitic and photochromic behaviour of this crystal. Using Kramers-Kronig-relations an estimation shows that the light-induced absorption changes can explain the observed refractive index changes. The observation of holographic writing with orthogonally polarized beams may by attribute to orientationally non-equivalent centers, which become anisotropic by the absorption of light after illumination. Yet, the nature of these centers is unclear. Further studies are already under way to clarify this point.

A theoretical model is developed which clarifies the reason for the appearance of a magnetic and/or optical anisotropy in garnets under illumination with linearly polarized light. The model is base on the calculation of the occupancies' kinetics of anisotropic impurity centers localized in different garnet sublattices. A comparison of experimental data for the magnetic yttrium-iron garnet doped with cobalt (YIG:Co) and the non-magnetic Ca3Mn2Ge3O12 (CaMnGe) garnet to the results of the model is performed which leads to a good agreement.

Light-induced change in the optical absorption of the garnet Ca3Mn2Ge3O12 has been found. The magnitude of the light-induced optical absorption does not depend on the polarization state of the exciting illumination. The effect persists for a long time at low temperatures and can be attributed to light-induced generation or redistribution of Mn4+ ions in the crystal.

Optical damage induced by infrared irradiation of proustite is investigated with holographic methods and photoelectron spectroscopy. Holographic writing results in thin absorption gratings located on the surface. This phenomenon is traced back to formation of Ag2S by a decomposition reaction on the surface of aged proustite crystals and generation of a metastable state of Ag2S by infrared light. The writing and erasing kinetics is studied by two-beam mixing with Nd3+-doped yttrium aluminium garnet laser radiation with lambda=1.06 mu m. The metastable absorption gratings induced on the surface reach a diffraction efficiency of a few per cent and have a storage time of 10(4) s.

The paramagnetic resonance of dilute ions in the bulk paramagnetic host is separated from the host response by means of optically detected magnetic resonance (ODMR) using the magnetic circular dichroism (MCD) of the absorption. This result shows that it is possible in principle to extend by means of the ODMR of the absorption the regime of paramagnetic resonance detection of impurity ions to magnetic hosts, which strongly interact with the microwave field and, hence, make the impurity signals unobservable by means of conventional EPR. The observed ODMR signals are attributed to and ions by correlation with the optical bands of these species. By means of ODMR via the Faraday effect it is shown that this effect is due to transitions between Tb levels. The identification of the observed magnetic resonance structures is confirmed by calculations based on known information on and in diamagnetic hosts. The role of molecular fields is discussed.

Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitroPrusside (SNP), $\rm Na_2[Fe(CN)_5NO] \cdot 2H_2O$, single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the $\rm [Fe(CN)_5NO]^{2-}$anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more than $\Delta n = 1 \times 10^{-3}$ in the red $(632.8$ nm) and $\Delta n = 5 \times 10^{-4}$ in the near-infrared region $(1047$ nm). The absorption coefficient is modulated by about $\Delta \alpha = 100$ m$^{-1}$ at $632.8$ nm and 40 m$^{-1}$ at 1047 nm. The wavelength dependence of $\Delta n$ can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiency $\eta$ depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along the $a$- and $b$-axis of the orthorhombic system.

Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitro-Prusside (SNP), Na2[Fe(CN)5NO] · 2H2O, single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the [Fe(CN)5NO]2− anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more thanΔn = 1 × 10−3 in the red (632.8 nm) andΔn = 5 × 10−4 in the near-infrared region (1047 nm). The absorption coefficient is modulated by aboutΔα = 100 m−1 at 632.8 nm and 40 m−1 at 1047 nm. The wavelength dependence ofΔn can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiencyη depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along thea- andb-axis of the orthorhombic system.

Elementary holographic gratings are recorded in Ca3Mn2Ge3O12 at 633 nm with orthogonal, linearly polarized writing beams at temperatures below 180 K. Refractive-index amplitudes of as high as 1.5 x 10(-4) are achieved at temperatures below 100 K. We analyze the dependence of the diffraction efficiency on the polarization of the recording beams. The time constant for writing at 100 K with a total intensity of 540 mW/cm(2) is 15.5 s. The temperature dependence of the holographically determined light-induced refractive-index changes can be described by Delta n(T) = Delta n(T = 0){1/[1 + r exp(-E(A)/kT]}, with an activation energy of 0.16 eV. (C) 1996 Optical Society of America.

Tetragonal calcium manganese germanium garnet (Ca3Mn2Ge3O12) is determined to be optically negative. An analysis of the angular dependence of the transmission for a-cut crystals reveals the presence of dichroism. Absorption is largest for extraordinarily polarized light. Both properties allow to determine and orient the crystallographic axes of Ca3Mn2Ge3O12 samples.

Analyzing anisotropic diffraction properties of photorefractive gratings in GaAs crystals and the symmetry difference of energy exchange between index-of-refraction and amplitude gratings, we identify three different kind of gratings, namely a photorefractive, a non-photorefractive index-of-refraction and a photochromic grating simultaneously occurring in semi-insulating GaAs crystals. We show that the latter two gratings probably originate from electric polarizability changes arising from spatial modulation of photoelectron traps occurring during photorefractive recording. Experiments are carried out using a continuous phase modulation technique in a two-wave mixing setup at a wavelength of 1.06 μm.

We report on the first observation of a photorefractive effect in the visible spectral range in a ferromagnetically ordered crystal. The maximum refractive index amplitude is about 3 × 10−6. The dark decay time at room temperature is above one hour. The photorefractive mechanism, yet not clear, is most likely not related to photomagnetism.

A photorefractive effect in terbium gallium garnet with refractive index changes up to Δn = 5 × 10−8 for elementary volume phase holograms is reported. The light-induced refractive index changes can directly be attributed via Kramers-Kronig relations to the observed photochromic and light-induced, linear dichroitic behavior. This can also explain the possibility of writing holograms with orthogonally polarized beams.

We present a method to determine the dielectric relaxation time using a phase-modulation technique. The predictions were checked using a GaAs crystal. The experimental results agree well with the theory.

We present here a theoretical and experimental analysis of photorefractive two-beam coupling in undoped GaAs as a function of temperature. Three major features are experimentally observed, firstly, a change of sign of the photorefractive beam coupling gain around 150 K, secondly, an enhancement of the space charge field by a factor 2 compared to the diffusion field and, finally, a strong peak of the absorption grating amplitude around 150 K. A photorefractive model is established that includes the metastable state of the EL2 defect with its optical properties (optical generation and optical recovery). It predicts all observed features correctly and is in good agreement with the experimental data.

We present a theoretical and experimental analysis of photorefractive two-beam coupling in undoped GaAs as a function of temperature. The theoretical treatment includes the metastable state of the EL2 defect with its optical properties (optical generation and optical recovery) in the photorefractive model. Three major features are predicted by this model: First, a change of the sign of the photorefractive beam coupling gain around 150 K; second, an enhancement of the space-charge field by a factor of 2 compared to the diffusion field; and, finally, the appearance of a strong peak due to an absorption grating around 150 K. All these features are actually observed experimentally with a good correlation between experimental data and theoretical simulation.

physica status solidi (b)Volume 182, Issue 2 p. K91-K93 Short Note Refractive Index of Terbium Gallium Garnet U. Schlarb, U. Schlarb Fachbereich Physik der Universität Osnabrück Search for more papers by this authorB. Sugg, B. Sugg Fachbereich Physik der Universität Osnabrück Search for more papers by this author U. Schlarb, U. Schlarb Fachbereich Physik der Universität Osnabrück Search for more papers by this authorB. Sugg, B. Sugg Fachbereich Physik der Universität Osnabrück Search for more papers by this author First published: 1 April 1994 https://doi.org/10.1002/pssb.2221820238Citations: 22 Barbarastr. 7, D-49069 Osnabrück, Federal Republic of Germany. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume182, Issue21 April 1994Pages K91-K93 RelatedInformation

A new holographic observation technique for 180° domains is demonstrated with a cerium-doped strontium barium niobate sample containing two antiparallel ferroelectric domains. The method relies on the fact that the phase shift of holographically written refractive-index gratings is +π/2 or -π/2 with respect to the initial light interference pattern depending on the orientation of the domains. As a consequence, readout of these gratings creates at the exit face of the sample new interference patterns shifted by 0 or π with respect to the initial one. These patterns, providing an image of the domain structure, are observed by microscope.

Diffraction and two-beam-coupling from mixed, i.e. phase and absorption gratings, with a grating vector in the (111)-plane are analyzed theoretically for cubic crystals of point symmetry 4̄3m. The diffraction efficiency does not depend on the grating orientation in the plane. Polarization of the diffracted beams varies with the grating orientation.

Diffraction and two-beam-coupling from mixed, i.e. phase and absorption gratings, with a grating vector in the (111)-plane are analyzed theoretically for cubic crystals of point symmetry 43 m. The diffraction efficiency does not depend on the grating orientation in the plane. Polarization of the diffracted beams varies with the grating orientation.