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The authors describe a technique for fabricating submicron domain inversion structures in MgO:LiNbO3. The method is based on controlled backswitched poling with short voltage pulses. Using this method, short periodic structures consisting of submicron domain patterns have been achieved in Z-cut MgLN crystal. The structure is fully compatible with nonlinear optical integrated waveguide applications. High performance of the submicron domain inversion structure is also demonstrated by evaluating its potential as second harmonic generation. [ABSTRACT FROM AUTHOR]

Photorefractive properties of congruent lithium niobate crystals codoped with HfO2 and Fe2O3 were investigated and it was found that Fe ions are still located at Li sites as photorefractive centers when the doping concentration of HfO2 goes above the threshold value. As a result, their photorefractive response speed and sensitivity are significantly enhanced. Meanwhile, the high saturation diffraction efficiency is still maintained. Experimental results definitely show that Hf is now the most effective doping element for LiNbO3:Fe crystal to improve its photorefractive properties. [ABSTRACT FROM AUTHOR]

We investigated the light-induced backward scattering in doubly doped lithium niobate crystals and observed an intensity threshold effect. It will be shown that scattering microregions are locally recorded in the sample by holographic interaction due to the existence of the threshold effect. Experimental results of multilayer recording point out that this property could be used for high-density multilayer-like bit data optical storage while keeping high signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

A method to determine the focal length of a thermal lens and pumping laser beam waist in the gain medium in laser-diode-pumped solid-state lasers is presented. This method, using resonator transform circle theory, is both simple and reliable. The measured focal length of the thermal lens is used to calculate the beam waist of pumping laser inside the gain medium. The effect of the thermal lens on the output power is also measured and analyzed. [ABSTRACT FROM AUTHOR]

LiNbO[sub 3] crystals with a composition close to stoichiometry were prepared by using a vapor transport equilibration (VTE) technique. The influence of the intrinsic defect density in the electric field periodic poling LiNbO[sub 3] crystal is studied. The switching field is found to decrease with the intrinsic defects. The reduction of intrinsic defects is mainly due to a change in the Li/Nb ratio in the LiNbO[sub 3] crystal, as a result of lithium diffusion during the VTE process. The switching field of ∼2 kV/mm in stoichiometric LiNbO[sub 3] is about one fourth of the previously published results obtained with near-stoichiometric crystals, and is approximately one tenth of the conventional congruent field. Periodic poling of thicker stoichiometric substrates was successfully performed by means of an electric field poling process at room temperature. [ABSTRACT FROM AUTHOR]

This letter reports three new absorption steps appearing by the long wavelength side of the UV intrinsic absorption edge of β-BaB[sub 2]O[sub 4] crystal at low temperatures We suggest that these new absorption steps should be attributed to the transitions of the indirect excitons bound in the centers of certain neutral impurities contained in the crystal specimens. [ABSTRACT FROM AUTHOR]

Presents an experiment which provided a change in the model of the defect structure in the LiNbO3:Mg, Fe Crystal, using OH absorption spectra. Method used to conduct the experiment; Definition of LiNbO3 crystal; Results of the experiment.

Uses a developed high-sensitivity photoacoustic (PA) cell to determine the absorption coefficient in several nonlinear-optical crystals. Profile of the PA cell; Method used to detect the power change; Comparison between results of the PA and laser calorimetric methods.

Presents a study that obtained nonlinear refractive index changes for the wavelengths near the fundamental edge in an ultrapure epitaxial layer gallium arsenide by the photoreflectance method. Electric field effect for pump intensities; Effect of plasma screening; Band filling effect for pump intensities.

• Single crystal fibers combine the advantages of crystals and fibers. • Laser is amplified with tapered fiber-single crystal fiber hybrid amplifier. • The quantum loss at 976 nm is more than 30 % lower than that at 940 nm. • Single-stage single crystal fiber outputs picosecond laser power exceeding 100 W. This paper introduces a compact picosecond laser system using tapered double cladding fiber-single crystal fiber hybrid amplification technology for the first time. By modifying the Ginzburg-Landau equation, we established a simulation model and designed a passive mode-locked picosecond oscillator based on a semiconductor saturable absorber mirror. The oscillator outputs laser with a pulse width of 7.75 ps, a center wavelength of 1030.55 nm, and a spectrum width of 0.58 nm. The seed laser is stretched and amplified by the all-fiber front stage, and then injected into the tapered double cladding fiber-single crystal fiber hybrid amplifier. The laser power is amplified from 820 mw to 103.1 W, obtaining a gain of 21 dB. We used zero-phonon line pumping technology in single crystal fiber amplifier to reduce the thermal effects caused by quantum loss, thereby increasing the length of the crystal and increasing the power loading capacity. We designed a single crystal fiber amplification module using Yb:YAG with 60 mm long, 1 mm diameter and a 1 at.% doping rate for the first time. Finally, a hundred-watt level picosecond laser output with a repetition frequency of 26.33 MHz, an average power of 103.1 W, a pulse width of 244.72 ps, a spectrum width of 1.16 nm, and a beam quality of M2 x = 1.368 and M2 y = 1.511 was obtained. To the best of our knowledge, this is the highest picosecond laser output power for an all-fiber front-stage combined with a single-stage single crystal fiber amplifier. [ABSTRACT FROM AUTHOR]

• Design of high optical efficiency dual-pass resonant cavity. • Picosecond laser regenerative amplifier without compression. • Good beam quality ultrafast laser system. • Zero-phonon line pumping technology with low quantum loss and thermal effects. This paper introduces a CPA-free Yb:YAG thin-disk regenerative amplifier laser system. The seed pulse is generated by a passive mode-locked picosecond oscillator based on a semiconductor saturable absorber mirror, with a center wavelength of 1030.7 nm, a pulse width of 7.7 ps, and a repetition frequency of 26.3 MHz. After stretched and pre-amplified by an all-fiber front stage, the seed with a pulse width of 201.3 ps and a pulse energy of 15.2 nJ was obtained, then injected into the thin-disk regenerative amplifier. Yb:YAG crystal was chosen as the material for the thin-disk, with 100 μm thickness, 9 mm diameter and 7 at.% doping rate. In order to increase the one-way round-trip gain of the thin-disk regenerative amplifier, a symmetrical dual-pass resonant cavity was designed to double the number of passing through the crystal on a round trip in the regenerative resonant cavity to reduce the times of cycles, intra-cavity loss and improve optical efficiency. We used a 969 nm fiber-coupled semiconductor laser as the pump source to pump the Yb:YAG thin-disk crystal. With zero-phonon line pumping technology, the quantum loss and thermal effect were reduced. In the end, we obtained a regenerative amplification output with an average power of 104.5 W, a repetition frequency of 200 kHz, a pulse width of 143.9 ps, and a spectrum width of 0.39 nm. The amplified pulse had quite good beam quality with M x 2 = 1.09 and M y 2 = 1.14. [ABSTRACT FROM AUTHOR]

• A miniature fiber-optic Fabry–Perot (F-P) accelerometer based on phase demodulation is demonstrated. • This structure is not only simple and easy to manufacture, but also greatly improves the performances of the accelerometer. • The F-P cavity length is demodulated by phase demodulation with abundant advantages of wide dynamic range, high resolution, independent of fiber loss and light intensity fluctuations. • The average sensitivity of the flat area is 17.55 µm/g and the transverse crosstalk is around 3 %. The resolution of the sensing system is 2.8 µg within a ± 3 mm maximum measurement. A miniature fiber-optic Fabry–Perot (F-P) accelerometer based on phase demodulation is demonstrated for improving sensitivity. The accelerometer is composed of a 11.5 mm diameter cylindrical outer frame, a spring-like diaphragm with a loaded mass block and optical fiber. This structure is not only simple and easy to manufacture, but also greatly improves the performances of the accelerometer. The F-P cavity length is demodulated by phase demodulation with abundant advantages of wide dynamic range, high resolution, independent of fiber loss and light intensity fluctuations. The inertial mass displacement indicating a variation in the F-P cavity length is demodulated and converted to acceleration. Through experimental verification, the resonant frequency of the accelerometer is 232 Hz, and axial sensitivity is flat in 30–180 Hz. The average sensitivity of the flat area is 17.55 µm/g and the transverse crosstalk is around 3 %. The resolution of the sensing system is 2.8 µg within a ±3 mm maximum measurement range by experimental tests. This work gives a fitting option to monitor low and medium frequency vibration in a large range of areas. [ABSTRACT FROM AUTHOR]

The friction and wear characteristic of self-mated alumina-reinforced zirconia-toughened mullite (ZTM/A) composites has been investigated using a block-on-ring tribometer in different lubricants at varying loads. Load-dependent wear transitions were observed for these ceramics. The wear transition was usually accompanied by an abrupt change of friction coefficient and wear rate. The addition of Al2O3 effectively reduces the wear rate of ZTM/A composites before the wear transition in water and at middle loads in machine oil. Scanning electron microscope (SEM) micrographs show that the main pre-transition wear mechanism of ZTM/A composites is plastic deformation, ploughing and occasionally grains pulling out, while fracture is the dominant mechanism of post-transition. Al2O3 can restrain the t→m phase transformation of zirconia to some extent and improve the resistance of these materials to wear by fracture, ploughing and plastic deformation. [Copyright &y& Elsevier]

Objective: To validate the efficacy and safety of Ningmitai capsule (NMT) in the patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS).Methods: We conducted a multicenter, randomized, double-blind, placebo-controlled trial in 120 men with CP/CPPS to evaluate the efficacy and safety of NMT. Participants were randomly assigned (1:1) to NMT or placebo treatment for 4 weeks at 3 centres. The patients were evaluated by the National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI) at baseline, the end of 2 and 4 weeks of treatment. The primary endpoints were the changes of the NIH-CPSI pain scores from baseline to the end of 2 and 4 weeks of the treatment. The secondary endpoints include the changes of the NIH-CPSI total scores, urinary symptoms scores and the quality of life (QoL) as well as the responder rate.Results: After 2 and 4 weeks of treatment, the mean decreases of the NIH-CPSI pain scores, total scores and QoL in the NMT group were all significantly superior to those in the placebo group. The responder rate was significantly higher in the NMT group than that in the placebo group at both 2 and 4 weeks. No adverse events were reported during the treatment.Conclusion: NMT could significantly improve the pain symptoms and QoL in the patients with CP/CPPS as early as in 2 weeks, and the efficacy enhanced at the end of the 4-week treatment. The safety of NMT was confirmed in this trial. [ABSTRACT FROM AUTHOR]

As a gold standard technique, enzyme-linked immunosorbent assay (ELISA) organically combines immunoreactions between antigens and antibodies with enzyme catalysis. The use of ELISA has contributed to advances in applications such as clinical diagnosis, food quality control, and environmental monitoring. However, conventional ELISA suffer from the moderate sensitivity and reliance on enzyme activity, which make it impossible to reliably and inexpensively detect trace targets. The nanotechnology boom has yielded exciting developments in designing nanomaterial-based improved ELISA in recent years. In this review, we attempt to comprehensively describe the improvements in ELISA methodology based on nanomaterials, with a focus on the mode of signal detection, such as colorimetric, fluorescent, electrochemical, photothermal, and Raman scattering sensing. We particularly emphasized on how nanomaterials are used as loading carriers, enzyme mimics, and signal reporters. This review concerns on partially representative examples and describes novel concepts and promising applications, rather than being exhaustive. Finally, we outline the challenges and perspectives, hopefully provide brief guideline to develop neotype improved ELISA. Image 1 • We reviewed 173 published articles to provide valuable information of ELISA. • Various nanomaterials serve as loading carriers, nano-enzyme, and signal reporters. • The merits of various signal mode are fully discussed in the improved ELISA. • Representative examples and promising applications are exhibited. • The challenges and perspectives of the improved ELISA are outlined. [ABSTRACT FROM AUTHOR]

The Raman spectra of three pure lithium niobate (LiNbO[sub 3]) crystals with different content of Li and several doped LiNbO[sub 3] (Mg, In and Ti) crystals have been investigated. A weak peak at about 738 cm[sup -1] reported as a very strong Raman peak of ilmenite phase LiNbO[sub 3] was observed for nonstoichiometric LiNbO[sub 3] crystals. The dependence of this peak on Li content and doping concentration in crystal suggested that there is a new kind of defect structure which has ilmenite-like stacking and direct relationship with antisite Nb[sub Li][sup 4+] ion. This result experimentally proved the existence of ilmenite-like stacking defect in nonstoichiometric LiNbO[sub 3] for the first time. This defect is in good agreement with the Li vacancy model and has a different structure from that proposed by Smyth [Ferroelectrics 50, 93 (1983); Proc. IEEE, p. 115 (1986)]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Objective: To study the feasibility of ultrasonography (US) as a replacement for CT during the diagnosis of ureteral calculi (UC). Materials and Methods: Clinical and imaging data of patients with UC between January 2013 and December 2017 were retrospectively analyzed. According to the imaging method, patients were divided into 3 groups: Group A, CT alone; Group B, CT and US, Group C, US alone. Age, location, and the size of stones were compared among the groups. According to the maximum diameter (MD) measured by using CT in Group B, patients were subdivided into 3 groups (subgroup 1–3): MD <0.5 cm, 0.5 cm ≤ MD ≤1.0 cm, and MD >1.0 cm. The MD measured by US and CT were compared in the subgroups. Results: A total of 1,289 patients with UC were admitted. The use of CT correlated with age (p = 0.000) and stone location (p = 0.004). The sensitivity and specificity of US were 71.3 and 100%. Positive US results correlated with stone size (p = 0.008), but not location (p = 0.861). The mean MDs of the calculi measured by US and CT: in subgroup 1:  0.80 ± 0.31 and 0.35 ± 0.05 cm (p = 0.000); in subgroup 2: 0.94 ± 0.32 and 0.72 ± 0.16 cm (p = 0.000); in subgroup 3: 1.75 ± 0.68 and 1.59 ± 0.52 cm (p = 0.094). Conclusions: US confirmed that UC do not require confirmatory CT. US can replace CT as the initial imaging examination of UC. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the relation between the amplitude of photoacoustic signals and the sample thickness when the sample wafer is perpendicular to the piezoelectric ceramics. Piezoelectric theory for perpendicular attachment; Experimental results; Conclusions.

Examines the variation of intensity of the photostimulated luminescence of barium-fluorine-chlorine-europium after ultraviolet irradiation with temperature. Application of x-ray powder diffraction; Relationship of the production rate of defects and temperature in alkali halides; Irradiation of ultraviolet light.

Presents a study that examined the growth and self-pumped phase conjugation of cerium-doped crystals. Preparation of the crystal sample; Measurement of the phase conjugation reflectivities of the samples; Determination of the time required for the initiation of the phase conjugate.

A high-sensitivity fiber-optic Fabry-Perot (F-P) photoacoustic gas detection system with properties of anti-electromagnetic interference and intrinsically safe was presented for quantitative analysis of SF 6 decomposition component H 2 S. Erbium-doped fiber amplification was combined with acoustic resonance amplification to enhance the photoacoustic signal. A fiber-optic cantilever acoustic sensor (FOCAS) was used to sense weak photoacoustic signals. To enhance the sensitivity and stability of photoacoustic signals detection, the effect of SF 6 gas on the responses of FOCAS and photoacoustic cell (PAC) was investigated. When SF 6 is the background gas, the resonance frequency of the PAC will be greatly reduced and the sensitivity of the FOCAS will be improved. With the excitation light power of 1 W and an averaging time was 200 s, the minimum detection limit (MDL) of H 2 S gas in the SF 6 background reached 14 ppb, and the normalized noise equivalence absorption (NNEA) was calculated to be 3.14 × 10−9 cm−1·W·Hz−1/2. The combination of excitation enhancement and detection enhancement of the photoacoustic signal solves the problem that the traditional sensor is difficult to improve the detection sensitivity due to the low absorption coefficient of H 2 S gas in the near-infrared region. • A fiber-optic cantilever acoustic sensor is used to detect weak photoacoustic signals in SF 6 background gas. • The acoustic resonance effect of PAC in SF 6 background gas was investigated. • The acoustic response characteristics of cantilever in SF 6 was studied. • The minimum detection limit of H 2 S gas in the SF 6 background reached 14 ppb. [ABSTRACT FROM AUTHOR]

To realize all-optical passive detection of CH 4 in narrow spaces and harsh environments, a compact cantilever-enhanced fiber-optic photoacoustic sensor (CEFPS) resistant to electromagnetic and ambient noise interference is proposed. Through theoretical analysis and finite element simulation, a miniaturized photoacoustic cell (PAC) with diffusion holes has been designed and fabricated. The diffusion holes are used for the circulation of the gas to be measured and attenuate the external noise coupled into the PAC. The concentration information of CH 4 is obtained by demodulating the vibration amplitude of the built-in cantilever generated by the photoacoustic pressure. The design of the built-in cantilever structure avoids the possibility of mechanical damage and reduces the interference of external noise in the detection of photoacoustic signals. The experimental results and the Allan-Werle deviation analysis of the CH 4 signal show that the minimum detection limit (MDL) is 0.32 ppm with an integration time of 60 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 2.44 × 10−8 cm−1 W/Hz1/2. The developed CEFPS achieves performance comparable to conventional resonant photoacoustic spectroscopy CH 4 detectors, although the volume is two orders of magnitude lower. • A miniaturized all-optical anti-interference cantilever-enhanced photoacoustic methane sensor is presented. • The cantilever acoustic-sensitive element and miniaturized photoacoustic cell (PAC) adopt a built-in design. • The direct effect of environmental noise interference, wind disturbance and mechanical damage on the cantilever is avoided. • The sensitivity of the sensor reaches the traditional resonant photoacoustic spectroscopy trace gas detection technology. • At the same time, the volume of the built-in miniaturized non-resonant PAC is reduced by about two orders of magnitude. [ABSTRACT FROM AUTHOR]

We designed and manufactured a set of high-sensitivity photoacoustic (PA) gas detector based on differential multi-pass cell (DMPC) with a chamber volume of only 162 mL, which realized real-time online monitoring of CH 4 in the atmosphere. The effective absorption optical path of DMPC reached 4.92 m, which enhanced the PA signal from the two dimensions of optical excitation and acoustic resonance. A 3D-printed muffler was integrated into the detector to eliminate the gas flow noise generated by the pump. A 1651 nm distributed feedback (DFB) laser was used to accomplish the measurement of CH 4. The analysis results showed that the minimum detection limit (MDL) of CH 4 reached 0.6 ppb with an averaging time of 500 s. In addition, the normalized noise equivalent absorption (NNEA) coefficient was 1.79 × 10−10 cm−1 W/Hz1/2. Continuous flow monitoring of CH 4 in the atmosphere was carried out to confirm the reliability and feasibility of the PA system based on DMPC. • A high-sensitivity photoacoustic (PA) gas detector based on differential multi-pass cell (DMPC) was presented. • A DMPC with 30 reflections for an effective absorption optical path length of 4.92 m was designed. • The minimum detection limit (MDL) reached 0.6 ppb with an integration time of 500 s. • The normalized noise equivalent absorption (NNEA) coefficient was equal to 1.79 × 10−10 cm−1 W/Hz1/2. • We have carried out continuous flow real-time detection of the concentration of CH 4 in atmosphere for 72 h. [ABSTRACT FROM AUTHOR]

Abstract: Several near-stoichiometric lithium niobate crystals with the doping concentration of Mg near the second threshold were prepared by vapor transport equilibrium technique. All these samples show no laser beam distortion under a light intensity of 26MW/cm2, that is three orders of magnitude higher than that of 5mol% Mg doped congruent LiNbO3. And the light-induced refractive index (Δn) in one of them is as small as 4.6×10−7, which is two orders of magnitude lower than that of congruent crystals. [Copyright &y& Elsevier]

Abstract: We describe the ultraviolet-light one-color photorefraction (UV-OPR) at 351nm in LiNbO3 crystals with different Mg-doping concentrations and [Li]/[Nb] ratios. It is shown that as the Mg-doping concentration and/or the [Li]/[Nb] ratio increase, the refractive index change and the two-beam coupling gain increase but the response time decreases. It is also shown that the recording sensitivity as large as ∼27cm/J is obtainable at a recording intensity of ∼1W/cm2 in near-stoichiometric LiNbO3 doped with 2mol% Mg. This sensitivity is approximately one order of magnitude higher than those for other LiNbO3 crystals. We also describe the ultraviolet-light-gating two-color photorefraction (UV-TPR) using 365nm gating and 633nm recording beams in LiNbO3 crystals with different Mg-doping concentrations and [Li]/[Nb] ratios. It is shown that UV-TPR is only observed in near-stoichiometric crystals and the grating-formation dynamics strongly depend on the Mg concentration. [Copyright &y& Elsevier]

Abstract: The ultraviolet absorption edges of LiNbO3 crystals with different Li2O contents and MgO doping concentrations were investigated. The generally defined absorption edges at absorption coefficient or 20 cm−1 of all these crystals fit the Urbach rule perfectly. The origin of this absorption edges in non-stoichiometric LiNbO3 crystals is attributed to the presence of Li vacancies. [Copyright &y& Elsevier]

Abstract: A melt supplying double crucible technique was described. Nearly stoichiometric lithium niobate (NSLN) crystals were grown in a lower crucible with a melt composition of [Li2O]/[Nb2O5]=58/42, and the melt was continuously added from a higher crucible. The composition of the adding melt was [Li2O]/[Nb2O5]=36/64, far away from the stoichiometric point of 50/50. NSLN crystals of 3in. were successfully grown, and the average concentration of Li2O was 49.85mol% with a radial composition deviation of ±0.02mol% and an axial composition deviation less than ±0.03mol%/cm. [Copyright &y& Elsevier]

Abstract: Two optical methods for determination of the composition in lithium tantalate were discussed. Quantitative relationships between the line width of Raman peaks (142cm−1 for E phonon and 861cm−1 for A1 phonon) and the crystal composition were firstly presented. The comparison of the Raman data obtained for the congruent and the near-stoichiometric crystals reveals some differences in the shape and the number of Raman peaks, which lead to a new assignment of the long-wavelength optical phonons. The OH− absorption bands of lithium tantalate crystals were measured at room temperature, and the line width of one decomposed peak was found to change considerably with the crystal composition, irrespective of the hydrogen concentration. The quantitative relationship between the line width of this peak and the crystal composition is also presented. [Copyright &y& Elsevier]

Abstract: Near-stoichiometric lithium niobate crystals doped with iron were prepared by vapor transport equilibration (VTE) method. The gain coefficient of these samples were measured and compared to the near-stoichiometric lithium niobate crystals prepared by double-crucible method, and the diffraction efficiency, recording time and erasing time were also done. The dynamic range coefficient (M/#) and homogeneity of the composition in the crystals were investigated too. [Copyright &y& Elsevier]

Abstract: The Raman scattering spectra of lithium tantalate crystals with different compositions were investigated. The comparison of the Raman data obtained for the congruent and the near-stoichiometric crystals reveals some differences in the shape and the number of Raman peaks, which lead to a new assignment of the long-wavelength optical phonons. And quantitative relationships between the linewidth of Raman peaks (142cm−1 for E-phonon and 861cm−1 for A1-phonon) and the crystal composition were firstly presented. Two local Raman lines, 278 and 750cm−1, were found for the congruent crystals and attributed to the intrinsic defects, Li vacancy and anti-site Ta ion, respectively. [Copyright &y& Elsevier]

Abstract: Methyl orange is an excellent nonlinear optical material. Both ordinary intense modulation holograph and the polarization holograph can be recorded in the methyl orange-polyvinyl alcohol (MO-PVA) film. The polarization state relationship among two writing beams, reading beam, and diffraction beam can be used for construction all-optical Boolean logic gate. [Copyright &y& Elsevier]

Er3+,Tm3+-codoped NaY(WO4)2 crystal was prepared by using Czochralski (CZ) pulling method. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Such optical parameters as intensity parameters, spontaneous emission probabilities, branch ratios and lifetimes are calculated from absorption spectra with Judd–Ofelt theory. Transition processes of the energy levels of Er3+, Tm3+ are analyzed in details and the cross-relaxations: 1G4(Tm3+)+4I15/2(Er3+)→3F2(Tm3+)+4I13/2(Er3+), 1G4(Tm3+)+4I15/2(Er3+)→3F4(Tm3+)+4F9/2(Er3+) and 3H4(Tm3+)+4I9/2(Er3+)→3F4(Tm3+)+4S3/2(Er3+) or 2H11/2 between the two ions are put forward. Through the experiments, we have found that, in this crystal, Tm3+ strengthens luminescence of Er3+ in the green and red regions evidently. The above energy transfer processes provide potential applications of Tm3+ in Er3+-doped laser materials. [Copyright &y& Elsevier]

The OH- absorption spectra of low doped lithium niobate (LiNbO3) crystals have been investigated. Though no apparent band shift is observed in these absorption spectra, their shapes are quite different. In order to analyze the information on the defect structure underlying these OH- absorption bands, the normalization and difference methods were employed. It was found that although the doping concentrations are under the thresholds the doping ions have apparent affect to the site occupation of OH- ions. The OH- vibrations related to MgLi+ (Mg2+ occupying Li-site) and InLi2+ are 3483 and 3484 cm-1 in LiNbO3:Mg and LiNbO3:In crystals, respectively. The absorption peak of LiNbO3:Ti (2.5 mol%) crystal at 3487 cm-1 is mainly related to TiLi3+–OH- and the 3489 cm-1 peak of LiNbO3:Mg (5.0 mol%), Ti (10.0 mol%) related to MgLi+–OH-, TiNb-–OH- and TiLi3+–OH-. Doping with Na improves the peak intensity near 3466 cm-1 and induces a new absorption peak at 3470 cm-1. The absorption bands of LiNbO3 crystals codoped with trivalent ions are associated with the co-effect of the doped ions and have some different characteristics from mono-doped crystals. [Copyright &y& Elsevier]

Summary: Under varying intensities and polarization of the exciting light respectively, the photoinduced birefringence of azo dye polymer film placed between a pair of orthogonal polarizers is studied by measuring the transmitted intensity. It is concluded that the saturation and stable values of the transmitted intensity are all proportional to the intensity of exciting light. Both values also relate to the polarization direction of the exciting light, and when the angle θ between the polarization directions of the probe intensity and the exciting light is lager than 10°, the saturation and stable values of the transmitted light are all proportional to sin2 2θ. In addition, the birefringence of the sample was measured accurately by using a compensator. [Copyright &y& Elsevier]

When two coherent beams interfere in bacteriorhodopsin (bR) film with a very small crossing angle, degenerate multi-wave mixing appears. In this paper, the properties of degenerate multi-wave mixing in bR film were studied. By use of degenerate multi-wave mixing in bR film, we realized optical Boolean logic operations. [Copyright &y& Elsevier]

Off-congruent lithium niobate (LiNbO3) single crystal was prepared by vapor transport equilibration (VTE). The Li/Nb ratio was determined by means of indirect methods such as the lattice parameters, the fundamental absorption edge position and the IR vibrational spectrum. Comparison of the results of the VTE LiNbO3 with those of the congruent crystal and congruent composition melt added 6 wt% K2O. In all cases the Li2O content was found to be closer to 50% than that of the congruent composition melt added 6 wt% K2O. The homogeneity of the composition in the crystal was also investigated. The data presented in this work show that the VTE method can be effectively applied to produce LiNbO3 stoichiometric crystal. [Copyright &y& Elsevier]

We observed a light-induced fanning scattering in LiNbO3 at 750–850 nm, using femtosecond laser and without pumping. The fanning scattering is just like the ordinary one. After comparing the phenomena of some crystals, which were doped with different ions and one was oxided, and studying the threshold of the scattering, we think the scattering is owing to the small polarons formed by the self-gating of the bipolarons. [Copyright &y& Elsevier]