Direct near infrared photorefractive recording and pre-exposure controlled hole–electron competition with enhanced recording in undoped Bi12TiO20

We report the direct recording of electron-based photorefractive hologram in nominally undoped Bi₁₂TiO₂₀ crystals using 780 nm wavelength light without pre-exposure or any kind of previous processing. A lower intensity absorption grating is also detected. Pre-exposure with shorter wavelength produces an extended lifetime hole-based complementary grating on another photoactive center level and leads to enhanced recording.PACS 42.70.Nq; 42.70.Ln; 42.70.Gi; 42.65.Hw     

Large optical limiting of [60]fullerene-substituted terpyridine palladium nanoparticles

The optical-limiting (OL) properties of new palladium nanoparticles based on a C ₆₀ derivative are investigated using nanosecond laser pulses at 532 nm wavelength. The nanoparticles in chloroform solution exhibit better OL performances than C ₆₀in toluene. The main origins concerning the OL are discussed.     

Trimeric metallo-phthalocyanines with good performances for nanosecond optical limiting in solution

Optical limiting (OL) performances of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M = Zn for compound ZnPc and Cu for compound CuPc) were investigated by using the Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective non-linear absorption coefficient β_eff, the linear absorption coefficient α₀, limiting threshold F_th and the saturation density or energy density F_sat values were determined for the investigated compounds. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.     

1.53 μm photoluminescence from ErYb(DBM)<Subscript>3</Subscript>MA containing polymer

We investigated the optical properties of the ErYb(DBM)₃MA complexes and the ErYb(DBM)₃MA containing polymer. Absorption and photoluminescence spectra confirm that the presence of Yb³⁺ ions enhances luminescence efficiency of Er³⁺ ions. The full width at half maximum bandwidth (FWHM) is ∼80 nm wide around 1.53 μm wavelength. We also fabricated ErYb containing polymeric channel waveguides using reactive ion etching technique. As an input pump of 120 mW was used, a ∼1.53 μm spontaneous emission was obtained in a 4-mm-long waveguide. PACS 42.00.00; 42.70.Jk; 42.82.Et     

Compensation of the photoelastic birefringence of a polymer by doping with an anisotropic molecule

We report on a method to compensate the photoelastic birefringence of a polymer. In this method, a rod-like molecule that has a polarizability anisotropy was chosen and doped in a polymer. We demonstrated this method by compensating the negative photoelastic birefringence of poly(methylmethacrylate) at a wavelength of 633 nm. Homogeneous doping with 2.2 wt. % of trans-stilbene almost eliminated the photoelastic birefringence of the polymer. The photoelastic coefficient of the synthesized zero-photoelastic birefringence polymer was 0.057×10^-12 Pa^-1. We found that the photoelastic birefringence of poly(methylmethacrylate) was compensated by the motion of trans-stilbene in the polymer by the analysis of the infrared absorption spectrum. PACS 42.70.-a; 42.70.Jk; 78.30.Jw     

Optical limiting properties of trimeric metallo-phthalocyanines/polymer composite films

The nonlinear absorption and optical limiting properties of two trimeric metallo-phthalocyanines namely, 2,4,6-tris[2-oxa-9,10,16,17,23,24-hexa(hexylthio) phthalocyaninato M(II)]-s-triazine (M=Zn for compound ZnPc and Cu for compound CuPc) doped polyvinyl chloride (PVC) thin film in the nanosecond regime were investigated by using the open-aperture Z-scan technique. The measurements were performed using 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. OL parameters of the ratio of the excited state to ground state absorption cross-sections κ, the effective nonlinear absorption coefficient β_eff, the linear absorption coefficient α₀ and the saturation density or energy density F_sat values were determined. The results show that MPc/PVC composite displays much larger nonlinear absorption coefficient and lower saturable fluence for optical limiting when compared to the same Pc molecules in solution. The results indicated that both compounds exhibited good OL performances. ZnPc shows slightly better OL parameters than that of CuPc.     

Crystal growth and optical properties of Tm:La3Ga5SiO14 single crystals

High optical quality Tm:La₃Ga₅SiO₁₄ single crystals with dopant concentration of 1 at. % Tm³⁺ ions were grown by the Czochralski method. The structure was studied by the X-ray powder diffraction method. The absorption spectrum and fluorescence spectrum of Tm³⁺:La₃Ga₅SiO₁₄ crystals were measured at room temperature. PACS 42.70.-a; 42.70.Hj; 61.10.Nz; 61.66.Fn; 78.20.-e; 78.90.+t; 81.10.-h     

OPTICAL LIMITING EFFECT IN TWO PHTHALOCYANINES OBSERVED BY PICOSECOND PULSED LASER

Optical limiting (OL) properties of two phthalocyanines were investigated by using picosecond laser pulses at 532nm. The relative ratios k of the absorption cross section of the first singlet excited state to that of the ground state were approximately obtained by the analysis of the experimental results in which the reverse saturable absorption model of the three-energy-level scheme was employed. A significant comparison with fullerene C₆₀ was presented for OL. The OL mechanisms have been analysed in detail.     

Fabrication of microchip based on UV transparent polymer for DNA electrophoresis by F2 laser ablation

A microchip for DNA electrophoresis made of a new UV transparent polymer material (CYTOP) whose absorption edge is much shorter than 190 nm has been fabricated by F₂ laser ablation. F₂ laser ablation achieves high-quality microfabrication of CYTOP surface with little deterioration of the optical property and little debris deposition at etched area. The microchip in which the microchannel connected with two reservoirs was embedded was successfully fabricated by bonding the ablated sample to the virgin CYTOP sheet. The fabricated microchip was applied for DNA analysis by electrophoresis and succeeded in separating different base-pares (bp) of DNA from 50 to 766 bp with resolution of 100 bp. PACS 42.70.Jk; 52.38.Mf; 82.45.-h     

Two-photon absorption in TeO2-PbO glasses excited at 532 and 590 nm

Degenerate two-photon absorption (TPA) in a binary glass with composition TeO₂-PbO is reported. The TPA coefficient, α₂, obtained with nanosecond laser pulses at 532 and 590 nm, increases when the relative amount of PbO is increased. The maximum TPA coefficient, α₂= 12.6 cm/GW, is comparable to or larger than the values reported for crystalline semiconductors and other recently reported glasses. PACS 42.70.-a; 42.65.-k; 42.70.Ce; 42.62.Fi     

Sonochemical synthesis and structural characterization of a new nanostructured Co(II) supramolecular coordination polymer with Lewis base sites as a new catalyst for Knoevenagel condensation

A new Co(II) mixed-ligand coordination supramolecular polymer with composition [Co₂(ppda)(4-bpdh)₂(NO₃)₂]_n (1) (where, ppda = p-phenylenediacrylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) was synthesized using solvothermal, mechanochemical and sonochemical methods. Compound 1 and the new nanostructure have been characterized by single-crystal X-ray, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM). The thermal stability of compound 1 was also studied by thermal gravimetric analysis (TGA). The surface area of these compounds was determined by BET. The single-crystal X-ray data shows a new interesting two-dimensional coordination polymer (CP). In addition, the effect of various sonication concentrations of initial reagents, power of ultrasound irradiation and also the time on the size and morphology of nano-structured coordination polymer 1 were evaluated. Moreover, it has been demonstrated that the nanostructure of the CP1 can be used as a catalyst in Knoevenagel condensation reaction.     

C60介质反饱和吸收动力学

采用速率方程理论研究C₆₀分子实现反饱和吸收的动力学过程,以YAG倍频调Q脉冲激光照射C₆₀甲苯溶液,实验验证了理论模拟的正确性。还分析了分子各能级对反饱和吸收的贡献以及不同激光波长和脉宽对反饱和吸收的影响。 关键词：     

Enhanced optical limiting properties in suspensions of CdO nanowires

Optical limiting (OL) properties of CdO nanowires in water and ethanol were investigated by using nanosecond laser pulses at 532 nm. Experimental results show that suspension of CdO nanowires in ethanol exhibits better OL property than solution of C₆₀ in toluene and suspension of CdO nanowires in water. The dominant mechanism for the observed enhanced optical limiting in ethanol suspensions of CdO nanowires is due to nonlinear scattering.     

Sonochemical synthesis and characterization of new one-dimensional manganese(II) coordination polymer nanostructures

A new Mn(II) coordination polymer, [Mn (L₁)₂(NCS)₂]_n (1) [L₁ = 3,4-bis(4-pyridyl)-5-(2-pyridyl)-1,2,4-triazole] was synthesized by the reaction of ligand L₁ and mixtures of manganese(II) acetate and potassium thiocyanate using the heat gradient method. Compound 1 has been characterized by IR spectroscopy, elemental analyses and X-ray crystallography. The crystal structure of compound 1 was determined by single-crystal X-ray diffraction and shows a new interesting one-dimensional coordination polymer. Nanostructures of compound 1 have been synthesized by sonochemical method. The products were characterized by X-ray powder diffraction, scanning electron microscopy (SEM), and IR spectroscopy. The thermal stability of nano particles of compound 1 was studied by thermal gravimetric and differential thermal analyses.     

High-power picoseconds 355 nm laser by third harmonic generation based on CsB3O5 crystal

We report on the high average power third harmonic generation (THG) of a mode-locked picosecond laser in a CsB₃O₅ (CBO) crystal. The picosecond laser beam at 1064 nm is produced by a home-made 30 W master oscillator power-amplifier (MOPA) Nd:YVO₄ laser system. The maximum THG output at 355 nm is up to 5.4 W. We also investigate the phase matching angle at different temperatures. During high power operation, the temperature of the CBO crystal is set at a high temperature of more than 100 °C. The THG system has shown a fine long-term stability for more than two months of operation. PACS 42.55.Px; 42.55.Rz; 42.70.Mp; 42.70.Nq; 42.65.Ky     

12.95 mW sixth harmonic generation with KBe<Subscript>2</Subscript>BO<Subscript>3</Subscript>F<Subscript>2</Subscript> crystal

We obtained the second harmonic of a frequency-tripled Nd:YVO₄ laser at wavelength of 177.3 nm with 12.95 mW output by using an optically contacted KBe₂BO₃F₂-CaF₂ prism-coupled device with a 2.1 mm thick KBe₂BO₃F₂ crystal, which is to our knowledge the best result at this wavelength. PACS 42.65.Ky; 42.70.Mp; 42.55.Xi     

Nonlinear optical characterization of LaEr(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> thin films using the <Emphasis Type="BoldItalic">Z</Emphasis> -scan technique

The nonlinear optical properties of thin films of LaEr(MoO₄)₃ were studied using a ∼30 ps Nd:YAG laser at 532 nm with a repetition rate of 250 Hz. Closed aperture Z-scan measurement revealed a negative nonlinearity in the LaEr(MoO₄)₃. The nonlinear refractive index γ=1.38×10^-10 cm²/W and nonlinear absorption coefficient β=16.8×10^-6 cm/W were calculated from the Z-scan data. The fluorescent upconversion spectra were recorded with 980 nm excitation. An optical switching mechanism based on nonlinear absorption is also presented experimentally. PACS 81.15.Fg; 77.84.Bw; 33.50.Dq; 42.70.Mp     

Low threshold and high contrast polymer dispersed liquid crystal grating based on twisted nematic polarization modulator

An electrically tunable mode is proposed to overcome the bottleneck problem of a conventional polymer dispersed liquid crystal (PDLC) grating and realize its low threshold and high contrast through an alignment-controlled PDLC. The results indicate that the threshold voltage V_PP of the grating is as low as 0.75–0.8 V, the saturation voltage V_pp is 7 V and the contrast ratio of the grating reaches 245, which is about three times larger than the conventional PDLC grating. Stability testing indicates a stable state of contrast during a long time. PACS 42.40.Eq; 42.70.Df; 42.79.Kr     

Investigation of photo-induced absorption in a Bi12TiO20 crystal

A photorefractive Bi₁₂TiO₂₀ (BTO) crystal is exposed with high intensity pulsed-laser beams 532 nm (the average intensity of the laser was 110 mW/cm², the average intensity per pulse was 2 MW/cm²), and the photo-induced dynamics of the absorption between 480 and 900 nm are studied and explained by two long-lived energy levels in the forbidden band. The relaxation times of the long-lived energy levels are experimentally found to be 10⁴ and 10⁵ s. The hysteresis character of the absorption coefficient is discussed. PACS  42.70.Mp; 42.70.Gi     

Light-induced absorption instability in weakly reduced congruent Er:LiNbO3 crystal

Light-induced absorption (LIA) characteristics in weakly reduced (or strongly annealed) congruent and/or vapor transport equilibration (VTE)-treated Er-doped LiNbO₃ crystals have been investigated in comparison with their corresponding as-grown ones and undoped crystals by using a polarized 632.8-nm beam as probe light and another polarized 632.8- or 488-nm beam as pump light. Under He-Ne pump, the LIA was observed only in strongly reduced pure VTE LiNbO₃ crystal. Under 488-nm pump, LIA is still not observed in the doped or undoped as-grown crystals. The weakly reduced VTE-treated Er(0.2 mol %):LiNbO₃ crystal displays weak and stable LIA. On the other hand, the corresponding weakly reduced congruent crystal displays a rather unpredictable light-induced absorption instability phenomenon. The instability was shown by the random competition of the LIA and light-induced transparency (LIT). When both crystals were further reduced, the VTE sample still shows stable LIA but with increased LIA, while the LIA in the congruent sample also becomes stable enough. The instability was experimentally proved to be associated with the presence of the Er³⁺ ion that performs the role of an extrinsic defect instead of photoluminescence. A three-level model is suggested that consists of a deep level (the bipolaron) and two shallow levels: the small polaron level and the level with respect to the Er³⁺ ion. The model has been employed to qualitatively explain the LIA characteristics of the weakly reduced congruent Er:LiNbO₃ crystal, including the the instability, the effect of the state of reduction, the pump intensity and the pump–probe polarization dependences. The inhomogeneity of the defects caused by the weak reduction and the simultaneous participation of the two shallow levels in the light-induced electron-transport process result in the random competition between LIA and LIT, and consequently result in the LIA instability. PACS 42.70.Hj; 42.70.Ln; 42.70.Mp; 42.65.Hw; 81.05.-t