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1.
We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.  相似文献   

2.
0.61 Ba0.39Nb2O6, SBN61), either by proton or helium ion implantation. Proton-implanted samples show a large increase of dark conductivity that reduces or even prevents the recording of refractive index gratings. For waveguides formed by helium implantation this effect is absent, and they can be used for efficient holographic recording. Photorefractive properties of the waveguides are investigated by two-beam coupling. After implantation with 2.0 MeV He+ and doses of (0.5-5)×1015 cm-2, the samples have to be polarized again, because heating or charge effects at the crystals surface during the implantation process decreases or even reverses the effective electrooptic coefficients in the waveguiding layer. For repoled samples, we find logarithmic gain coefficients of up to 45 cm-1 with time constants for the build-up of the purely π/2-shifted refractive index grating of the order of 1 ms for the blue lines of an Ar+ laser. Photoconductivity depends nonlinearly on light intensity with an exponent x≈0.55. With increasing implanted helium dose, both electronic and nuclear damage of the waveguiding layer grows, and the photorefractive properties of the waveguides are considerably degraded. Received: 20 February 1997/Revised version: 1 May 1997  相似文献   

3.
The observation of a novel noncollinear optical second-harmonic generation mechanism is reported. In strontium barium niobate crystals, a circular cone of second-harmonic light is generated when a fundamental beam of intensive laser light is directed along the crystallographic c axis. It can be shown that the effect is caused by the nonlinear polarization of antiparallel ordered ferroelectric microdomains.  相似文献   

4.
Ionoluminescence spectra for different rare-earth ion (Pr3+ and Eu3+)-activated SrxBa1?xNb2O6 strontium barium niobate crystals (x=0.33 and 0.60) have been induced with a 3 MeV proton beam for a variety of beam current intensities (45, 40 and 20 nA). The proton-beam induced luminescent spectra have shown features associated with the presence of the rare-earth ion and some spectral features mostly related to the host crystal, which appear only for high beam current intensities. We have compared the ionoluminescence results to those obtained under UV light excitation (photoluminescence technique) where a direct excitation of the band gap would occur.  相似文献   

5.
The anomalies of polarization (mismatch of hysteresis loops for several first repolarization cycles, the absence of specific coercive field, etc.) in quasi-static and dc electric fields have been found in the strontium barium niobate relaxor ferroelectric. The anomalies are associated with a highly inhomogeneous structure of the crystal, which is considered a clearly defined nonergodic system with a random distribution of strong local internal fields. The energy distributions of potential barriers for the polarization and the depolarization are obtained at different electric field strengths and temperatures.  相似文献   

6.
7.
This paper reports the results obtained in strontium barium niobate (SBN) nanocrystals in glasses doped with 1, 2.5 and 5 mol% of Er3+ ions. The melt-quenching method was applied to fabricate the glasses with composition SrO–BaO–Nb2O5–B2O3 and further thermal treatment was used to obtain glass ceramic samples from the glass precursor. X-ray diffraction patterns confirmed the formation of SBN nanocrystals with an average size of about 50 nm in diameter. Time-resolved fluorescence spectra for the emission of Er3+ ions at 1550 nm have been analyzed in order to confirm the incorporation of the Er3+ ions into the nanocrystals. Green frequency upconversion emission under excitation at 975 nm coming from the ions in the nanocrystals has been obtained. This intense upconversion is about a factor of 500 higher than that obtained from the ions which reside in the glassy phase. Moreover, temporal evolution studies have been carried out with the purpose of determining the involved upconversion mechanism and the importance of these processes as a source of losses for the optical amplification at 1550 nm.  相似文献   

8.
The study of two different methods to obtain strontium barium niobate nanocrystals immersed in a glass matrix has been carried out. Ho2O3-doped SrO-BaO-Nb2O5-B2O3 glasses were fabricated using the melt quenching method. Glass ceramic samples were obtained from the precursor glass by thermal treatment in a furnace and by laser irradiation. These glass ceramic samples are formed by a glassy phase and a crystalline phase of strontium barium niobate nanocrystals. This structure was confirmed by X-ray diffraction and Atomic Force Microscope images. The incorporation of Ho3+ ions in the strontium barium niobate nanocrystals were corroborated by optical measurements, which produced an increment in the luminescence intensity compared to the precursor glass.  相似文献   

9.
The specific features of jump-like pulse processes of spontaneous polarization switching in relaxor ferroelectric crystals of strontium barium niobate are investigated. Based on the fixed parameters of the jump-like switching pulses, three possible mechanisms of their formation are revealed.  相似文献   

10.
Light-induced holographic scattering is investigated in photorefractive Sr0.61Ba0.39Nb2O6 (SBN) crystals, in which diffusion charge transport dominates. A crystal is illuminated with two coherent pump beams and different scattering patterns are observed on a screen behind the crystal. We attribute the patterns to certain phase-matching conditions, which allows the identification of the parametric processes that are involved . PACS 42.65.Hw; 42.70.Nq  相似文献   

11.
Lu F  Meng MQ  Wang KM  Liu XD  Chen HC  Shen DY 《Optics letters》1997,22(3):163-165
The first planar optical waveguide to the authors' knowledge has been formed in Cu-doped potassium sodium strontium barium niobate crystal by mega-electron-volt He(+) implantation. Both TE and TM modes are observed. The profiles of the ordinary and the extraordinary refractive indices are deduced from dark-line mode spectroscopy. The results show that the mega-electron-volt He implantation results in a decrease in refractive index in barriers for both n(o) and n(e), but for n(e) there is an obvious increase in the waveguide region. From an experiment in photorefractive two-wave mixing, it is found that the erasure time for two-wave mixing is prolonged by ion implantation.  相似文献   

12.
We report on the photorefractive properties of a Cr-doped (K1–x Na x )2A–2 (Sr y Ba1–y )2–A Nb10O30 (x=0.586, y=0.659, A=1.12) single crystal in the near-infrared spectrum. The sample exhibits photorefractivity for wavelengths up to at least 840 nm where the steady-state two-beam coupling gain is found to be larger than 2 cm–1. Photorefractive gain and decay rate are measured as a function of wavelength, grating spacing and intensity. The wavelength dependence of gain fluctuations in two-beam coupling are also measured.  相似文献   

13.
康祥喆  叶辉 《物理学报》2006,55(9):4928-4933
采用溶胶-凝胶法在氧化镁单晶衬底上制备了符合化学计量比的完全填充型铁电钾钠铌酸锶钡(KNSBN)薄膜,通过X射线衍射,摇摆曲线,X射线Φ扫描,扫描电子显微镜等方法研究了薄膜的微结构,采用Adachi法研究了薄膜的电光特性. 实验发现,KNSBN薄膜在氧化镁(001)单晶衬底上沿c轴外延生长,K+,Na+的引入有效地提高了薄膜的横向电光系数r51. 成分为K0.2Na0.2Sr0.24Ba0.56Nb2O6, K0.2Na0.2Sr0.6Ba0.2Nb2O6, K0.2Na0.2Sr0.72Ba0.08Nb2O6的三种KNSBN薄膜的r51值分别为108.52pm/V, 119.98pm/V, 126.96pm/V,r51的数值随Sr2+含量增加而增大. 关键词: 横向电光系数 钾钠铌酸锶钡 外延生长  相似文献   

14.
The influence of doping of the SrxBa1?x Nb2O6 (x=0.61) crystals (SBN-0.61) by rare-earth element (RE) dopants has been investigated. Taking into account the data available in the literature, it is demonstrated that the introduction of all rare-earth metals is accompanied by a substantial decrease in the temperature of the phase transition T p and an increase in its smearing. The shift in the T p temperature for certain rare-earth metals ranges up to 20 K per atomic percent of dopant in the crystal. It is experimentally established that, in the SBN-0.61: Yb, SBN-0.61: Ce, SBN-0.61: Tm, SBN-0.61: La, and SBN-0.61: (Ce + La) crystals, a decrease in T p brings about a considerable increase in the permittivity and the piezoelectric and electrooptical coefficients. The conclusion is drawn that the doping by rare-earth metals provides a means of optimizing the properties of strontium barium niobates. The pulse switching of the SBN-0.61 and SBN-0.61: RE crystals is studied for the first time. It is found that the switching is characterized by a number of features, the most important of which is a decrease in the switched charge after the application of external fields. This effect associated with the specific features of the switching in the relaxor ferroelectric is assumed to be responsible for the instability of the parameters for strontium barium niobate material.  相似文献   

15.
Two-wave mixing with a small angle between beams in a photorefractive crystal biased with an external electric field leads to the formation of additional non-Bragg orders and to wave amplification. A steady-state gain of 25 cm (-1) was obtained for an external voltage of 3 kV/cm in strontium barium niobate. Noise amplification and oscillation are also demonstrated.  相似文献   

16.
A planar optical waveguide was formed in calcium barium niobate (CBN) crystal by 2.8-MeV He-ion implantation with a dose of 1.0×1016 ions/cm2 at room temperature. The prism-coupling method was used to take dark mode measurements at both 633 nm and 1539 nm. The refractive-index profile (no and ne) of the He-implanted CBN waveguide was analyzed with the reflectivity calculation method. The results show that the MeV He implantation results in a decrease in refractive index in barriers for both no (4.1%) and ne (3.1%), but for ne there is an increase in the waveguide region. The intensity profile of the guide mode and waveguide loss were obtained by end-fire coupling. PACS 42.79.Gn; 61.80.Jh  相似文献   

17.
The ferroelectric properties of relaxor ferroelectric materials Sr x Ba1 − x Nb2O6 of different compositions have been investigated using scanning probe microscopy and macroscopic polarization methods. An analysis of the results obtained from microscopic and macroscopic measurements of the hysteresis loops has demonstrated that a frequency dependence of the coercive field E c is observed at frequencies f in the range from 0.03 to 250 Hz, so that the coercive field E c regularly decreases with decreasing frequency. The observation of the kinetics of domains under a direct-current voltage applied to the probe of the atomic force microscope has revealed a lateral motion of domain walls in response to electric fields EE c . This result qualitatively explains a slow polarization relaxation occurring for a giant time in Sr x Ba1 − x Nb2O6.  相似文献   

18.
Two-beam coupling gain and speed of Cr-doped strontium barium niobate in the visible and near-infrared spectral regions are measured. It is found that the sample still exhibits the appreciable photorefractive gain in the near-infrared spectrum. Photorefractive parameters such as effective trap density, effective electrooptic coefficient and mobility · recombination-time product are obtained from the measurement. The photorefractive spectra of the coupling gain and speed in the sample are compared with those of Cr-doped KNSBN.  相似文献   

19.
Relaxor ferroelectrics are known to show a low-temperature behaviour that quantitatively resembles the features of canonical glasses. In order to get a comprehensive characterisation of the responsible low-energy excitations, single crystals of strontium barium niobate were investigated below 10 K. The density of localised states was obtained from heat capacity, and their coupling to phonons from sound velocity and thermal conductivity. The presence of slowly relaxing systems could be estimated from heat release data, respectively.

In contrast with structural glasses, however, SBN and further relaxor ferroelectrics show an energy dependent density of states and an upper limit of the relaxation time spectrum. Considering these properties, which appear to be typical also for other glassy crystals, a modification of the standard tunneling model is proposed.  相似文献   

20.
We have obtained stationary bright spatial solitons in a planar photorefractive strontium barium niobate waveguide for visible light ranging from 514.5 to 780 nm. Even for larger wavelengths (lambda=1047 nm) strong self-focusing of the beam was observed; however, input power had to be some orders of magnitude higher than for visible light for self-focusing to occur. Furthermore, we found transient self-trapping of red light (lambda=632.8 nm) that corresponds to the formation of bright quasi-steady-state solitons.  相似文献   

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