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1.
We study experimentally the formation of refractive index voxels (volume elements) in photorefractive LiNbO3 and LiTaO3 crystals illuminated with high irradiance femtosecond laser pulses. We used 150 fs pulses at 800 nm wavelength (energy 6–50 nJ) tightly focused inside the crystals in a single shot regime. This resulted in a formation of a micrometer size region of elevated refractive index, which may be used as memory bits in information storage/retrieval application. The maximum refractive index change of 5×10−4 was recorded in undoped LiNbO3 at an average light intensity of ∼TW/cm2 that is close to the breakdown threshold. A simple setup for photorefractive recording and in situ monitoring of the refractive index changes has been proposed. M. Sūdžius leaves from: the Institute of Materials Science and Applied Research of Vilnius University, Lithuania.  相似文献   

2.
Ce:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios were grown by the Czochralski method from melts having compositions varying between 48.6 and 58 mol% Li2O. The Ce, Li and Nb concentrations in the grown Ce:Fe:LiNbO3 crystals were analyzed by the inductively coupled plasma atomic emission spectrometer (ICP-AES). It was found that as the [Li]/[Nb] ratio increases in the melt, the [Li]/[Nb] ratio in the crystal and the distribution coefficients of Ce ions increase also. The photorefractive properties of the Ce:Fe:LiNbO3 crystals were experimentally studied by the two-wave coupling method. The results show that as the [Li]/[Nb] ratio increases, the dynamic range decreases, but the photorefractive sensitivity and the signal-to-noise ratio improve. In a coherent volume 0.192 cm3 of a Ce:Fe:LiNbO3 crystal with [Li]/[Nb] ratio of 1.2, 3800 holograms with 800×600 pixels have been successfully multiplexed in a compact volume holographic data storage system.  相似文献   

3.
The hard X-ray yield generated with femtosecond laser pulses is studied for differently chirped irradiating laser pulses. The radiation of a Ti:sapphire CPA laser system (29 fs, 750 μJ, 1 kHz) is focused onto an iron containing solid state target producing incoherent hard X-ray radiation, Bremsstrahlung as well as target-specific Kα and Kβ lines. The hard X-ray yield has been optimized by introducing negative and positive group delay dispersion (GDD) and third order dispersion (TOD) to the femtosecond laser pulse. The Kα yield could be enhanced by a factor of 1.7 and reached 1.9×108 Fe Kα photons/s in 4π with the laser pulse positively chirped, and 1.5×108 Fe Kα photons/s with the pulse negatively chirped. When the pulse energy is lowered to about 400 μJ the yield maximum at negative chirp vanishes and only the maximum at positive chirp remains. We explain this behavior with an increased electron temperature caused by the induced GDD and TOD in the pulse. PACS 42.65.Re; 52.38.Ph; 52.50.Jm  相似文献   

4.
马致考 《光子学报》1998,27(8):724-728
本文提供一种测量两束相干的ps光脉冲的空间二维时间振幅相关函数的新方法.在此方法中,光脉冲是被记录在一种光致折变的体积全息介质中,而所记录的信息可以通过直接量度在介质中所形成的光栅的空间分布而读出.这种方法可的可行性已为实验证实,它是通过3.5ps倍频锁模Nd:YAG激光测量光致折变晶体LiNbO3来实现的。  相似文献   

5.
Using methods of electronic spectroscopy, laser conoscopy, photoinduced (photoreactive) light scattering, and Raman light-scattering spectroscopy, we have studied the optical homogeneity, optical transmission, and photorefractive properties of single crystals LiNbO3:Mg(5.21 mol %) and LiNbO3:Fe(0.009 mol %):Mg(5.04 mol %) that were grown from congruent melts. We have ascertained that doping with “nonphotorefractive” Mg2+ cations causes suppression of the photorefractive effect in a lithium-niobate crystal. Upon double doping (Fe:Mg), if the concentration of Mg2+ cations exceeds the threshold concentration, the photorefractive effect is almost not observed and the presence of “photorefractive” Fe cations does not affect the photorefractive effect as strongly as in congruent crystals doped with Fe.  相似文献   

6.
The near-stoichiometric LiNbO3 crystal co-doped with In2O3, Fe2O3, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm−1 absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO3 crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO3 crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO3 crystal is a promising candidate for blue photorefractive holographic recording.  相似文献   

7.
采用了不同能量的单脉冲和多脉冲飞秒激光对LiNbO3晶体进行烧蚀,并刻蚀了表面衍射型光栅.通过扫描电镜和原子力显微镜观察了烧蚀点的形貌特征,首次发现利用单束飞秒激光脉冲对LiNbO3晶体烧蚀,可以得到超衍射极限的烧蚀点,当聚焦光斑直径约为2μm、能量为170nJ的单脉冲飞秒激光作用时,烧蚀点的直径约为400nm,100nJ,17个脉冲作用时烧蚀点的直径约为800nm.同时可以观察到在能量较低的多脉冲飞秒激光作用下, LiNbO3晶体呈现出大约200nm周期性分布的波纹状结构.实验结果表明,选择合适参数的飞秒激光脉冲可以对LiNbO3晶体进行超衍射极限加工,这对于利用飞秒激光制作LiNbO3基质的微纳光电子器件有十分重要的意义.  相似文献   

8.
In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO3 crystals on photorefractive effect induced in these crystals by Gaussian Ar+ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO3: Fe and LiNbO3: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl2). The space and time dependences of the refractive index changes induced by the Ar+ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction.  相似文献   

9.
We have investigated the photorefractive (photoinduced) light scattering in lithium niobate single crystals: LiNbO3, LiNbO3:B, LiNbO3:Y(0.46 mas %), LiNbO3:Y(0.24):Mg(0.63 mas %), and LiNbO3:Ta(1.13):Mg(0.0109 mas %) that were grown from congruent melts. We have found that the shape of the speckle structure of this scattering and the kinetics of the development of its indicatrix depend substantially on the type of the impurity dopant in the lithium niobate crystal. We have observed that, upon laser irradiation of crystals doped with Y3+, Ta5+:Mg2+, and Y3+:Mg2+, the shape of their scattering indicatrix changes with time. At the same time, the LiNbO3:B crystal is characterized by a complete absence of time changes in its speckle structure, which indicates that the photorefractive effect in this crystal is substantially lowered.  相似文献   

10.
The results of the spectroscopic analysis of transition strengths for Er3+ ions in a series of Hf:Er:LiNbO3 crystals with variable Hf content and fixed Er content are reported. Unpolarized UV-VIS-NIR absorption spectra, upconversion fluorescence spectra excited at 800 nm, and microsecond time-resolved spectra excited at 400 nm and 800 nm by 800 nm femtosecond laser were measured at room temperature. The HfO2 incorporation has influence on Er3+ radiative lifetimes, and fluorescence branching ratios. For Hf(4 mol %):Er(1 mol %):LiNbO3, Ω2=2.63×10-20 cm2, Ω4=2.86×10-20 cm2, and Ω6=0.72×10-20 cm2. Ω24 is contrary to the Er3+ general trend of Ω246 when the Hf content is below its threshold concentration. In addition, the sum of Ω increases with the Hf content when the HfO2 content below 6 mol % is unfamiliar. The upconversion mechanism is discussed in this work. PACS 71.20.Eh; 77.84.Dy; 42.62.Fi; 42.65.Ky  相似文献   

11.
The photorefractive properties of LiNbO3∶Fe and LiNbO3∶Cu have been studied in combination with optical absorption-, Mössbauer- and EPR-measurements. The charge states of Fe in successively reduced LiNbO3∶Fe have been investigated with respect to the influence on the photorefractive sensitivity and saturation value of the refractive index change. The results of this experiment demonstrate clearly the close correlation between the concentration of Fe2+ impurities and the optical absorption band around 2.6 eV in LiNbO3∶Fe, which is known to give rise to an anisotropic charge transport upon optical excitation. The resulting photocurrents determine the photorefractive sensitivity mainly in the initial state of halographic exposure. With increasing conversion from Fe3+ to Fe2+ the photorefractive sensitivity saturates and the saturation value of the refractive index change decreases remarkably. In the case of LiNbO3∶Cu a similar behaviour of the photorefractive storage parameters after successive reduction treatments has been observed qualitatively. However, in contradiction to LiNbO3∶Fe the Cu2+ centers cannot be related to the photorefractive sensitivity of LiNbO3∶Cu. These results are discussed with respect to the predictions of two models concerning the microscopic nature of the photorefractive process in doped LiNbO3.  相似文献   

12.
The nonvolatile photorefractive characteristics of LiNbO3:Fe:Cu and In-doped LiNbO3:Fe:Cu crystals are investigated. The stronger nonvolatile blue photorefraction observed can be ascribed to its remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centers, which is one or two orders of magnitude higher than those obtained in conventional two-color recordings under the same recording conditions. Furthermore, it is interesting that, compared with LiNbO3:Fe:Cu, the recording properties, such as the saturation refractive index change, nonvolatile sensitivity and response time at 488 nm wavelength are enhanced in LiNbO3:In:Fe:Cu crystals under the same recording conditions. The so-called damage-resistant dopants such as In3+ ions in red photorefraction are not damage resistant at 488 nm wavelength but they enhance the blue photorefraction. PACS  42.40.Ht; 42.40.Lx; 42.70.Ln  相似文献   

13.
Zuo Xiaoxi 《Optik》2005,116(7):361-364
Fe:LiNbO3 and In:Fe:LiNbO3 crystals were grown by Czochralski method. The absorption spectra were measured to investigate their defect structure. The photo damage resistance and photorefractive properties were measured. The photo damage resistance of the In:Fe:LiNbO3 crystal in which the In concentration is above the threshold value is one order of magnitude higher than that of the Fe:LiNbO3 crystal. The mechanisms of the violet shift of the absorption edge and the enhancement of the photorefractive effect of In:Fe:LiNbO3 crystals were investigated.  相似文献   

14.
The near stoichiometric LiNbO3 crystals co-doped with ZrO2 and Fe2O3 have been grown from a Li-rich melt (Li/Nb=1.38, atomic ratio) by the Czochralski method in air atmosphere at the first time. The OH? absorption and UV–vis absorption spectra were characterized to investigate the defect structure of the crystals. The appearances of the 3479 cm?1 absorption peak and 358 nm absorption edge manifest that the composition of the grown crystal is close to the stoichiometric ratio. The blue holographic properties were also measured by the two-wave coupling experiments. As a result, in the near stoichiometric Zr:Fe:LiNbO3 crystals, photorefractive response speed, recording sensitivity, and two-wave coupling gain coefficient are significantly enhanced. Meanwhile, the high saturation diffraction efficiency is still maintained. These findings prove that the material of near stoichiometric Zr:Fe:LiNbO3 crystals are a promising candidate for blue photorefractive holographic recording.  相似文献   

15.
A series of LiNbO3 crystals doped with various concentrations of ZnO and fixed concentrations of RuO2 and Fe2O3 have been grown by the Czochralski method from the congruent melts. The type of charge carriers was determined by Kr+ laser (476 nm) and He–Ne laser (633 nm). The results revealed that the holes were the dominant charge carriers at blue light irradiation. Dual-wavelength and two-color techniques were employed to investigate the nonvolatile holographic storage properties of Ru:Fe:LiNbO3 and Zn doped Ru:Fe:LiNbO3 crystals. The essential parameters of blue nonvolatile holographic storage in Zn:Ru:Fe:LiNbO3 crystals were enhanced greatly with the increase of Zn concentration. This indicates that the damage resistant dopants Zn2+ ions enhance the photorefractive properties at 476 nm wavelength instead of suppressing the photorefraction. The different mechanisms of blue photorefractive and nonvolatile holographic storage properties by dual wavelength recording in Zn:Ru:Fe:LiNbO3 crystals were discussed.  相似文献   

16.
A few‐cycle, broadband, singly‐resonant optical parametric oscillator (OPO) for the mid‐infrared based on MgO‐doped periodically‐poled LiNbO3 (MgO:PPLN), synchronously pumped by a 20‐fs Ti:sapphire laser is reported. By using crystal interaction lengths as short as 250 µm, and careful dispersion management of input pump pulses and the OPO resonator, near‐transform‐limited, few‐cycle idler pulses tunable across the mid‐infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179‐3732 nm (4589‐2680 cm‐1) by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spanning over 422 nm (FWHM) recorded at 3732 nm. The effect of crystal length on spectral bandwidth and pulse duration is investigated at a fixed wavelength, confirming near‐transform‐limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio‐frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM00 mode profile. Photograph shows a multigrating MgO:PPLN crystal used as a nonlinear gain medium in the few‐cycle femtosecond mid‐IR OPO. The visible light is the result of non‐phase‐matched sum‐frequency mixing between the interacting beams.  相似文献   

17.
Influence of proton exchange and annealing on the photorefractive properties of Fe:LiNbO3 crystals has been investigated using two-wave coupling phenomena. The two-wave coupling phenomena results in microscopic interference pattern inside the sample which subsequently helps in the formation of refractive index grating. The diffraction efficiency of the crystal increases after proton exchange, whereas the reverse is observed on annealed samples. The former is attributed to an increase of extraordinary refractive index of the crystal, while the latter to the oxidization of Fe2+ to Fe3+.  相似文献   

18.
凌振芳  刘思敏  郭儒  张光寅 《物理学报》1991,40(11):1786-1791
本文按照Kukhtarev的光折变理论讨论了在LiNbO3:Fe晶体内自发形成的运动折射率相位栅和由它所引起的强烈的背向光折变散射。 关键词:  相似文献   

19.
When femtosecond laser pulses interfere with chirped femtosecond laser pulses in As2S3 fiber, a chirped fiber grating is formed. An analytical expression is given to describe the chirped grating, and its Bragg reflectivity is calculated. Because of the high photosensitive effect of As2S3 material, the chirped fiber grating has a wide Bragg reflective spectrum and high reflectivity by choosing proper parameters. This indicates that the chirped fiber grating can be used as a stretcher in the femtosecond chirped pulse amplification (CPA) system.  相似文献   

20.
The results of Er3+ ion spectroscopic analysis in Sc:LiNbO3 crystals were reported. The line strengths from the ground state to the excited state were evaluated from the measured unpolarized absorption spectrum and analyzed by using standard Judd–Ofelt theory. For Sc(3 mol. %):Er (1 mol. %):LiNbO3 crystal, the obtained intensity parameters are: Ω2=3.72×10-20 cm2, Ω4=1.07×10-20 cm2, and Ω6=0.98×10-20 cm2. The fluorescence spectra and microsecond time-resolved spectra were investigated in the visible region. The excited state absorption transition strengths at 800 nm excitation were evaluated based on Judd–Ofelt theory. The results obtained here were compared to results from other research on Er:LiNbO3 crystals. PACS 71.20.Eh; 77.84.Dy; 42.70.Hj; 42.62.Fi; 42.65.Ky  相似文献   

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