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ABSTRACT: A series of LN:Mo,Zr and LN:Mo,Mg crystals with different doping concentrations were grown and their holographic properties were investigated from UV to the visible range. Each crystal allows for holographic storage from UV to the visible as LN:Mo. When the concentration of MgO is enhanced to 6.5mol%, the response time can be dramatically shortened to 0.22 s, 0.33 s, 0.37 s and 1.2 s for 351, 488, 532, and 671 nm laser, respectively. The results show that LN:Mo,Mg is a promising candidate for all-color holographic volume storage with fast response.
Optics Express 05/2013; 21(9):10460-6. · 3.59 Impact Factor
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ABSTRACT: We developed a real-time imaging system to probe the light-assisted domain reversal process of Mg-doped LiNbO<sub>3</sub>. An interesting phenomenon was observed where the domain appeared to reverse just after the laser was obscured. An exclusive electric field of about 350 V/mm was measured at 532 nm of light irradiation at an intensity of 6.6 × 10<sup>4</sup> W/cm<sup>2</sup>. The exclusive electric field was considered to be produced by a pyroelectric effect owing to a temperature change in the region of irradiation. The temperature change in the light-irradiated region was calculated to be about 2.3°C. Our experimental results indicate that a change of the electric field caused by the pyroelectric effect may play a significant role when LiNbO<sub>3</sub> or other ferroelectric crystals are used under strong light.
Optics Express 12/2012; 20(27):29131-6. · 3.59 Impact Factor
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ABSTRACT: Molybdenum-doped lithium niobate crystals were grown under different polarization conditions and their holographic properties were investigated. In contrast to current dopants, hexavalent molybdenum prefers niobium sites. Thereby, holographic storage becomes possible from the ultraviolet to the visible with considerably lower response time. The response time of 0.5 mol. % Mo-doped LiNbO(3) can be especially shortened to as small as 0.35 s with a still high saturation diffraction efficiency of about 60% at 351 nm. Molybdenum-doped lithium niobate thus is a promising candidate for all-color holographic storage applications.
Optics Letters 07/2012; 37(13):2679-81. · 3.40 Impact Factor
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ABSTRACT: A series of vanadium-doped lithium niobate crystals was grown and their photorefractive properties were investigated with a 532 nm laser. At a total light intensity of 471 mW/cm(2), a short response time of only 0.57 s was achieved for 0.1 mol.% vanadium in LiNbO(3). The photorefractive process is dominated by the diffusion field instead of the photovoltaic field. The dominant charge carriers are electrons. The possible mechanism for the fast photorefractive response is discussed.
Optics Letters 06/2012; 37(11):1841-3. · 3.40 Impact Factor
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ABSTRACT: The ultraviolet (UV) band edge photorefractivity of Sn-doped LiNbO(3) (LN:Sn) at 325 nm has been investigated. A sharp decrease of beam distortion, which is accompanied by a significant increase in the photoconductivity, is observed in LN:Sn crystals with Sn-doping concentrations at or above 2.0 mol%. The diffraction efficiency, the holographic recording sensitivity and response rate, and the two-wave coupling gain coefficient are greatly enhanced when the Sn-doping concentration reaches 2.0 mol% or more. Unlike LiNbO(3) doped with Hf in which the UV gratings can be erased easily by a red beam, the UV gratings in LN:Sn can withstand long-term red beam illumination. Electrons are determined to be the dominant light-induced charge carriers responsible for the UV band edge photorefraction. The observed enhancement on the UV band edge photorefractivity is found to be associated with the showup of an absorption band around 325 nm in LN:Sn crystals with Sn-doping concentrations at or above 2.0 mol%.
Optics Letters 08/2011; 36(16):3163-5. · 3.40 Impact Factor
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ABSTRACT: The shape of the ferroelectric domain wall mainly depends on the lattice structure and the pinning effect of random defects, but can we control it intentionally? Here we present a method to bend the domain wall by a bubble. A submillimeter bubble was put underneath a lithium niobate wafer inside a deionized water electrode to resist the propagation of the domain wall, and make the straight wall bend at an angle of 52°. The perpendicular surface screening field was considered to directly relate to the bending angle and the motion of the surface charged droplets in the bubble, and the detachment of droplets determined the bending of the domain wall. Further experiments succeeded in varying the bending angle from 52° to 0° by changing the ion concentration of the liquid electrode.
Journal of Physics Condensed Matter 08/2011; 23(34):345901. · 2.55 Impact Factor
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ABSTRACT: We report on the observation of Čerenkov emission of a third-harmonic frequency in a two-dimensional nonlinear photonic crystal, where the second-order nonlinearity χ(2) is spatially modulated by the reversal of ferroelectric domains. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions.
Applied Physics Letters 06/2011; 98(24):241114-241114-3. · 3.84 Impact Factor
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ABSTRACT: A series of vanadium-doped lithium niobate (LN:V) crystals has been grown and their photorefractive properties were investigated. For 0.1 mol. % V-doped LiNbO(3), a fast photorefractive response of 160 ms was obtained with a 351 nm laser and a total light intensity of 583 mW/cm(2). The measurements of the x-ray photoelectron spectrum and electron paramagnetic resonance show that V(3+), V(4+), and V(5+) ions exist in these LN:V crystals. V(3+) and V(4+) ions correspond to the 420 and 475 nm absorption peaks, respectively. The fast photorefractive response and high sensitivity indicate that LN:V is a suitable candidate for UV photorefractive applications.
Optics Letters 05/2011; 36(10):1779-81. · 3.40 Impact Factor
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ABSTRACT: Near-stoichiometric zirconium-doped lithium niobate crystals were fabricated and their optical damage resistance was investigated. It was found that these crystals can withstand a light intensity of 20 MW/cm2 at 514.5 nm cw laser, 80 GW/cm2 at 532 nm pulse laser, and 120 kW/cm2 at 351 nm cw laser. The minimum switching field is only 1.00 kV/mm for 0.5 mol% zirconium-doped lithium niobate crystal. These properties suggest that the near-stoichiometric zirconium-doped lithium niobate crystals will be an excellent candidate for quasi-phase matching technique.
Optics Express 01/2011; 19(3):1743-8. · 3.59 Impact Factor
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ABSTRACT: We report simultaneous generation of multiple conical second-harmonic waves in a two-dimensional nonlinear photonic structure when illuminated by two overlapping noncollinear fundamental beams. We show that this phenomenon is caused by the nonlinear Čerenkov radiation emitted due to the interaction of photons from each constituent fundamental beam as well as the virtual one propagating along the bisector of the two beams. In addition, by studying the asymmetric geometry of the interaction, we uniquely verify the effects of reciprocal vectors on the Čerenkov-type second-harmonic generation in nonlinear photonic structures.
Optics Letters 11/2010; 35(22):3790-2. · 3.40 Impact Factor
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ABSTRACT: We study frequency conversion via interaction of two fundamental beams in quadratic nonlinear media with random distribution of the ferroelectric domains. We demonstrate broadband second- and third-harmonic generation, analyse both spatial and polarization properties of the emitted harmonics and show that they closely follow the theoretical predictions.
Journal of Physics B Atomic Molecular and Optical Physics 10/2010; 43(21):215404. · 1.88 Impact Factor
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ABSTRACT: OH− absorption bands of both congruent and near-stoichiometric LiNbO3:Hf crystals were investigated. The abrupt blueshift of OH− absorption bands was found between the doping levels of 2 and 2.5 mol% in the congruent crystals, which confirms the exact optical-damage threshold for Hf doping. The absorption difference of OH− bands between the congruent and near-stoichiometric crystals shows that after Li incorporation H+ ions no longer prefer the sites of 3500 cm−1. Moreover, with the increase of Hf doping in the near-stoichiometric crystals, H+ ions were found to gradually transfer to the sites of 3489 cm−1. These results are explained by the breakdown of the association of HfNb− and H+ ions and the subsequent redistribution of H+ ions around HfLi3+ ions in VLi−-deficient lattice. Additionally, the link between the intrinsic defects and how they influence the optical-damage threshold upon adding Hf was discussed in detail.
EPL (Europhysics Letters) 08/2010; 91(3):36002. · 2.17 Impact Factor
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ABSTRACT: Ultrafast carrier dynamics were investigated in a delafossite CuScO2, a material with a remarkably large binding energy of exciton ( ∼ 0.4 eV), using femtosecond transient transmission spectroscopy. Differential transmission spectra showed dispersive structures in the excitonic resonance energies. We have observed a delayed rise-up on a time scale of 10 ps, suggesting slow carrier cooling. It is followed by a slower decay, time constant of which corresponds to the lifetime of exciton (approximately 0.75 ns). These results were analyzed in terms of the generalized many-body Elliott model, accounting for a screening effect of excitons.
Applied Physics Letters 05/2010; 96(21):211904-211904-3. · 3.84 Impact Factor
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ABSTRACT: We report on the light scattering phenomenon in annealed multidomain LiNbO3:Fe:Hf crystals. The scattering sources are found to be some fog-like "defects", which cause the polarization-dependent scattering of the light, and can be removed completely by the illumination of visible light. Based on these results and the etch patterns, these "defects" are suggested to be refractive index fluctuations induced by the space charges accumulated at the boundary of opposite microdomains. The influence of quick heating-up on the "defects" is also studied and the results firmly support our suggestion about the nature of the "defects". At last, the temporal curves of the transmitted intensity during the light scattering are explained. The mechanism for the opposite microdomain formation is also explained from the view of crystal growth.
Optics Express 05/2010; 18(11):11949-54. · 3.59 Impact Factor
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ABSTRACT: Light-induced domain reversal of near-stoichiometric Mg-doped LiNbO <sub>3</sub> crystal was investigated with a focused 532 nm continuous laser beam. The lowest electric field applied to accomplish domain nucleation is only 30 V/mm and 1/80 of the coercive field, which is safe and convenient for us to fabricate domain structures. Under this superlow applied field, the pinning effect of domain wall is so obvious that the inverted domain reveals a gear shape contrary to the hexagon in a higher applied field. Then two-dimensional domain patterns with the smallest domain size of 4 μ m have been fabricated.
Journal of Applied Physics 04/2010; · 2.17 Impact Factor
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ABSTRACT: We have designed and grown triply doped LiNbO(3):Zr,Cu,Ce crystal and investigated its characteristics of nonvolatile holographic storage. It's observed that the photorefractive sensitivity of LiNbO(3):Zr,Cu,Ce has improved to 0.099 cm/J, which is about one order of magnitude larger than that of congruent LiNbO(3):Cu,Ce. And LiNbO(3):Zr,Cu,Ce also has high suppression to light-induced scattering. Our results indicated that triply doped LiNbO(3):Zr,Cu,Ce is an excellent candidate for nonvolatile holographic data storage.
Optics Express 03/2010; 18(6):6333-9. · 3.59 Impact Factor
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ABSTRACT: Applications of lithium niobate in nonlinear optics at high light intensities are seriously hampered by optical damage. Recent investigations have shown that Hf(4+) and Zr(4+) ions have some advantages in suppressing optical damage of LiNbO(3) with respect to Mg(2+). Here we present Sn-doped LiNbO(3) (Sn:LN). Experimental results indicate that Sn:LN has similar optical damage resistance to Mg-doped LiNbO(3), but the doping threshold of Sn is only 2.5 mol.%, where its distribution coefficient is 0.98. Hence Sn(4+) ion turns out to be another good choice for increasing optical damage resistance of LiNbO(3).
Optics Letters 03/2010; 35(6):883-5. · 3.40 Impact Factor
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ABSTRACT: We studied the photorefractive effect of lithium niobate ( LiNbO <sub>3</sub>) doped with Mg, Zn, In, Hf, or codoped with Mg and Fe at an ultraviolet (UV) wavelength down to 325 nm. It is found that the UV photorefraction of LiNbO <sub>3</sub> doped with Mg, Zn, In, or Hf was enhanced significantly as compared to that of the nominally pure LiNbO <sub>3</sub> . Our results show that the property of resistance against photorefraction in highly Mg, Zn, In, or Hf doped LiNbO <sub>3</sub> is true only in the visible and near-infrared wavelength range. By contrast, these crystals exhibit excellent photorefractive characteristics at UV wavelength of 325 nm, even better than those at 351 nm. For example, the photorefractive two-wave coupling gain coefficient Γ and the photorefractive recording sensitivity at 325 nm were measured to be ∼38 cm <sup>-1</sup> and 37.7 cm/J, respectively, in a LiNbO <sub>3</sub> crystal doped with 9 mol % Zn. The photorefractive response time of a Mg : LiNbO <sub>3</sub> with a 9 mol % Mg was measured to be 73 ms with a total recording intensity of 614 mW / cm <sup>2</sup> at 325 nm. In highly Mg, Zn, In, or Hf doped LiNbO <sub>3</sub> crystals, diffusion dominates over photovoltaic effect and electrons are the dominant charge carriers in UV photorefraction at 325 nm. The results are also of interest to the study on the defect structure of LiNbO <sub>3</sub> near to the absorption edge.
Journal of Applied Physics 03/2010; · 2.17 Impact Factor
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ABSTRACT: The UV photorefractivity of LiNbO(3):Hf was investigated by beam distortion and two-wave coupling experiments. A sharp decrease of beam distortion was found between Hf concentrations of 2 and 2.5 mol.%, indicating a significant increase of photoconductivity there. The energy-transfer direction of the two-wave coupling and the effect of chemical reduction on the UV photorefractivity reveal that electrons are the carriers responsible for the UV photorefraction. Moreover, dissimilar with LiNbO(3) highly doped with Mg, Zn, and In, the grating recorded in LiNbO(3):Hf was found to be nearly stable in the dark but sensitive to red light, which can be attributed to the special location of Fe ions in the crystal lattice.
Optics Letters 02/2010; 35(4):601-3. · 3.40 Impact Factor
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ABSTRACT: The UV photorefraction of Zr-doped lithium niobate (LN:Zr) was investigated. The experimental results show that LN:Zr crystals have high resistance against photorefraction in the UV region as well as in the visible range and can withstand a UV light intensity of above 10(5) W/cm(2). According to the fitting results of erasing curves with UV and green light, a two-center O(2-/-)-defect model was suggested. Our results indicate that LN:Zr is an excellent candidate for optical damage resistance from the UV to the visible spectrum.
Optics Letters 01/2010; 35(1):10-2. · 3.40 Impact Factor
