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Through the first-principles density functional theory and the phonon Boltzmann transport equation, we investigated the phonon transport characteristics inside 1T-TiSe2. The calculation results of the lattice thermal conductivity (κl) show that the κl of TiSe2 is extremely low (1.28 W (m K)−1, 300 K) and decreases with the shrinkage of the sample size. Moreover, the results also prove the isotropic nature of thermal transport. By decomposing the contribution of the thermal conductivity according to the frequency, the κl of the single-layer TiSe2 is primarily attributed to the acoustic phonons and a small portion of optical phonons, with the frequency range of 0–4.5 THz. The calculation of the scattering rate further illustrates the competition of different scattering modes in this frequency range to verify the change in thermal conductivity of different sample sizes. The high scattering rate and low group velocity lead to the low thermal conductivity of the optical phonon mode in TiSe2. In addition, reducing the size of the system can significantly limit the thermal conductivity by eliminating the contribution of long mean free path phonons. When the characteristic length of the single-layer TiSe2 is about 14.92 nm, κl reduces to half. Our results also show that TiSe2 has an extremely high Gruneisen parameter (about 2.62). Further decomposition of the three-phonon scattering phase space and scattering rate demonstrates that in the range 0–4.5 THz, the absorption process is the main conversion form of phonons. We conclude that, due to the high Gruneisen parameter, the high anharmonicity in TiSe2 leads to the extremely low κl. This study provides κl related to the temperature, frequency, and MFP, and deeply discusses the phonon transport in TiSe2, which has great significance to further adjust the thermal conductivity to develop highly efficient thermoelectric materials and promote the application of devices based on TiSe2.

Hydrogenated diamond-like carbon (DLC) film was prepared on the stainless steel by plasma enhanced chemical vapor deposition technique and its tribocorrosion behaviors under different lubricating conditions were investigated. The results show that the hydrogenated DLC film exhibits superior tribocorrosion resistance than the steel substrate in water. The addition of graphene oxide (GO) in water can further improve the tribocorrosion resistance of the DLC film. The excellent tribocorrosion resistance of the DLC film lubricated with the GO dispersed in water is attributed to the high hardness and chemical inertness of the DLC film and the deposited film of GO nanosheets on the wear surface that has lubrication function for reducing wear and acts as barrier layer against corrosion during rubbing process.

Graphene oxide (GO) nanosheets and onion-like carbon (OLC) nanoparticles were synthesized from natural graphite powder and candle soot, respectively, and characterized by transmission electron microscopy and Raman spectroscopy. The lubricating performances of GO and OLC as lubricant additives in water were comparatively evaluated using a ball-on-disc tribometer. The effects of sand blasting of a steel disc on its morphology and tribological property were evaluated. The results show that the two nanomaterials, GO and OLC, when used as lubricant additives in water effectively reduce the friction and wear of the sliding discs, which is independent of the disc surface treatment. On applying heavy loads, it is observed that GO exhibits superior friction-reducing and anti-wear abilities compared to those of OLC—a trace amount of GO can achieve a lubricating ability equivalent to that of an abundant amount of OLC. Furthermore, it is observed that sand blasting cannot improve the wear resistance of the treated steel disc, even though the hardness of the disc increased after the treatment. The possible anti-wear and friction-reducing mechanisms of the GO and OLC as lubricant additives in water are discussed based on results for the wear surfaces obtained by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy

Through a series of molecular dynamics (MD) simulations, the interfacial thermal transport between liquid water and single-layer graphene film on the silicon substrate was studied. Three factors were justified for the interfacial thermal transport including interfacial interaction strength, water film thickness and water density. The results show that the interfacial heat transport capacity exhibits a significant dependence on the interaction strength, and this change in interfacial thermal conductance (ITC) was verified by calculating the vibrational density of states (VDOS). Meanwhile, dramatic oscillation was observed in the density of the liquid water near the wall, indicating that the motion law of water molecules was affected by the interaction force at the interface. Further study on the effect of water film thickness and density on the interfacial thermal transport, it is found that there is a critical value for the ITC with the change of water film thickness. When the water film thickness is greater than 4 nm, the effect on the interfacial thermal transport is not obvious, and the ITC gradually tends to a stable value. However, for the liquid water density, the ITC basically shows an increasing trend with the increase of density. In addition, the solid–liquid interface spacing was found to be variability and the distance is determined by the thickness and density of the water film.

A highly sensitive and visible-light-driven photoelectrochemical (PEC) sensor has been constructed for the quantitative assay of organophosphorus pesticides like chlorpyrifos (Chlo) using hollow Co9S8@CdS heterostructures. The Co9S8@CdS heterostructures were created by growing CdS onto Co9S8 surface via one-step oil-bath route, of which Co9S8 was fabricated with hollow tubular structures through the Co(CO3)0.35Cl0.2(OH)1.1-templated solvothermal method. It was discovered that the so-obtained Co9S8@CdS with direct Z-scheme heterojunctions could exhibit larger photocurrents than the Co9S8 or CdS because of the greatly enhanced separation efficiency of photo-generated carriers. What’s more, the photocurrent signal of Co9S8@CdS-based PEC sensor could be selectively inhibited with the addition of Chlo through the specific chelation between the N and S atoms of Chlo with C N and P S groups and Co sites of Co9S8@CdS so as to suppress the carriers transferring. The developed PEC sensor could exhibit a linear response for Chlo ranging from 0.050 to 1000 ppb, with the detection limit value down to 0.015 ppb, which was far below than those of currently reported PEC sensors. Besides, the proposed routes may provide guidelines for designing various direct Z-scheme heterojunction-based PEC analysis platforms for determining environmental pollutants like Chlo.

With the development of fuel cell products and technology, power electronics researchers have proposed a variety of fuel cell DC/DC power supply topologies for the output characteristics of fuel cells. This article compares and analyzes several existing non-isolated and isolated topological structures, summarizes the respective advantages and disadvantages of different topological structures and applicable scenarios, and provides references for further indepth discussion of related issues.

Graphene/GaN nanocomposites have important applications in GaN-based LEDs. Since the electrical transport characteristics of this composite have been widely studied, the thermal transport properties have not been systematically studied. Herein, the thermal transport properties of suspended graphene and graphene supported by GaN including length, substrate effect and temperature dependence are carefully studied by molecular dynamics (MD) simulation. When the length is 250 nm, the thermal conductivity of GaN-supported graphene is 1567.5±46.4 W/mK, which is about 85% of that for the suspended graphene at room temperature. More interesting, a theoretical model is used to describe substrate effect by modifying the phonon dispersion and density of states, and the conclusion of this model is consistent with our MD simulations. Moreover, the underlying mechanism of substrate effect and temperature dependence is revealed by spectral energy density (SED) analysis. Our study reports the finite suppression of GaN on the thermal conductivity of graphene, which provides insights for thermal management of GaN-based LEDs.

A near-infrared (NIR) light-driven photoelectrochemical (PEC) sensing platform was established for the quantitative assay of Hg2+ using Ag@Ag2S nanocomposites. Ag2S quantum dots (QDs) with the bead-chain-like nanostructure were fabricated simply via one-step oil-bath route to be further deposited with metallic Ag through the photo-reduction method to yield Ag@Ag2S nanocomposites. It was found that Ag@Ag2S-based sensor could present more than twice larger PEC responses than the Ag2S-based one, due to the synergetic combination of metallic Ag with the surface plasmon resonance (SPR) effects and Ag2S QDs with the NIR-light-irradiated PEC properties. More importantly, the developed PEC sensor could display the photocurrent responses that are selectively inhibited in the presence of Hg2+ by forming Ag-Hg amalgam to accelerate the recombination of photo-induced electron-hole pairs. Under NIR light, it can detect Hg2+ in the concentrations linearly ranging from 0.0010 to 5.0 nM, with a limit of detection of about 0.50 pM. This work may guide a promising combination of Ag2S of NIR QDs with metallic Ag of SPR effects for designing various PEC sensing platforms for the complex environmental monitoring of different heavy-metal ions like Hg2+.

The magnetization behaviors in Sm–Ni–Fe–Cu alloys at low temperatures have been investigated. It was found that the hysteresis loops show wasp-waisted character at low temperatures, which has been proved to be related to the existence of multi-phases, the Fe/Ni soft magnetic phases and the CaCu 5 -type hard magnetic phase. A smooth-jump behavior of the magnetization is observed at T >5 K, whereas a step-like magnetization process appears at T 5 -type phase is responsible for such abnormal magnetization behavior. The magnetic moment reversal model with thermal activation is used to explain the relation of the critical magnetic field ( H cm ) to the temperature ( T >5 K). The reversal of the moment direction has to cross over an energy barrier of about 6.6×10 −15 erg. The step-like jumps of the magnetization below 5 K is proposed to be resulted from a sharp increase of the sample temperature under the heat released by the irreversible domain wall motion.

Visible-light-driven and ultra-stable CoSx/CdS photocatalysts were controllably fabricated by the ZIF-67-templated one-pot solvothermal route for highly efficient photocatalytic Cr(VI) reduction. It was discovered that the resulting CoSx/CdS composites could present different photocatalytic activities controllably depending on the CoSx-to-CdS molar ratios used. The one with 1/16 M ratio could display the highest photocatalytic reduction performance for Cr(VI) with the efficiency up to 100% within 30 min, which is 5.6-fold and 2.1-fold higher than that of pristine CoSx and CdS, respectively. Herein, the components of CoSx and CdS with well-matched energy-band structures might serve separately as the electrons donor and the holes quencher to prolong the lifetime of photogenerated electrons in CoSx/CdS composites. A direct Z-scheme heterojunction could be thus constructed for promoting the charge carrier transferring with the improved redox abilities, leading to the robust photocatalysis of CoSx/CdS photocatalyst. Moreover, the developed CoSx/CdS photocatalyst could present superior stability with the structure and activity well survived after five photocatalytic cycles. This work may pave the way towards the controllable construction of a direct Z-scheme photocatalytic system by synergistically combining two kinds of components with matched energy-band structures, achieving the enhanced photocatalysis for the wide applications in the environmental remediation field.

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for probing Hg2+ with “turn-on” signal output using hollow CoSx@CdS polyhedron as direct Z-scheme photocatalyst and Hg2+-recognition probe. The CoSx@CdS heterojunction photocatalysts were fabricated by growing CdS nanoparticles on the surface of cobalt sulfide (CoSx) via one-pot solvothermal route using metal-organic frameworks (MOFs) of ZIF-67 polyhedrons as the sacrificial templates and cobalt precursors. It was discovered that the photocurrent responses of the CoSx@CdS-modified ITO electrodes could be specifically turned on by Hg2+, in contrast to these of the CoSx or CdS-modified ones showing no significant Hg2+-induced photocurrent. Under visible light irradiation, herein, the synergetic combination of CoSx and CdS components could improve the carriers transferring of PEC system. More importantly, the photocurrents of the PEC sensor could be greatly enhanced in the presence of Hg2+ through the selective ion-exchange reaction to trigger the in-situ formation of a new Z-scheme heterojunction of CoSx@CdS/HgS photocatalysts, achieving the further promoted charge transferring and suppressed recombination of photogenerated electron-hole pairs. The developed double heterojunctions-based PEC sensors can detect Hg2+ with the concentrations ranging from 0.010 to 1000 nM, which performances are much better than those of the current PEC analysis methods. Besides, such a MOF-templated one-pot construction route may pave the way toward the design of various direct Z-scheme heterojunction photocatalysts of PEC probes of great interest.

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg2+ by the synergetic combination of low-bandgap Ag2S and wide-bandgap ZnS quantum dots (QDs). Ag2S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag2S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag2S and ZnS QDs could act as the PEC sensitizer and Hg2+-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg2+ under the visible-light irradiation, presumably due to that Hg2+ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag2S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg2+ with concentrations ranging from 0.010-1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg2+ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg2+ evaluation.

Silicon power semiconductor device is difficult to meet the requirements of high temperature, high pressure and high frequency. Among them, the MOSFET which has the fast switch speed and the simple driving circuit, become the most popular object in SiC power electronic devices. In this paper, we choose the C2M0160120D chip of CREE company, establishing a complete model. And the static characteristics of SiC MOSFET under different temperature points are simulated. The switching characteristics of SiC MOSFET under different driving resistances are analyzed and compared with the experimental results, and the accuracy of the model is verified in this paper.

In this paper, a femtosecond laser micromachining system to fabricate a microfiber Fabry-Perot (F-P) cavity, and a real-time system to monitor interferometric intensity of F-P cavity have been developed. The relationships of fringe visibility of an F-P cavity on parallelism and surface roughness are analyzed and discussed. In order to eliminate the slope of the cutting section coming from the focusing optics, precompensation and double machining are introduced. The fringe visibility of a F-P interferometric sensor which exceeds 15 dB has been realized.

A fiber tunable high-power picosecond laser system has been for the first time demonstrated. A gain switch semiconductor laser diode was introduced as seed source, and a multi-stage single mode Yb-doped fiber amplifier was combined with a single mode double-clad Yb-doped fiber amplifier to construct the amplification system. High stability and good beam quality pulses with 1MHz tunable repetition rate, 3W average power, 90ps pulse duration, and central wavelength tunable from 1053 nm to 1073 nm were generated. The completely fiber integrated approach has the potential to be scaled to significantly higher average powers.

Pulses of 177 fs and 1035 nm, with average power of 1.2 mW, have been generated directly from a passively mode-locked Yb-doped figure-of-eight fiber laser, with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. To our knowledge, these are the shortest pulses ever to come from a passively mode-locked Yb-doped figure-of-eight fiber laser. This represents a 5-fold reduction in pulse duration compared with that of previously reported passively mode-locked Yb-doped figure-of-eight fiber lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0 MHz.

Exchange bias (EB) effect has been intensively studied for more than half century due to its applications in spintronics devices, such as giant magneto resistance (GMR) read heads and magnetic random access memory (MRAM).[1] Except for conventional ferromagnetic (FM)-antiferromag-netic (AFM) system, EB has also been reported in other magnetic systems, such as ferromagnetic (FM)-ferromagnetic (FIM) system, spin glasses (SG) and nanoparticles with surface spin disorder. The most studied FM-FIM system is the Fe/Fe 3 O 4 core shell structure. It is believed that the inter-facial SG state plays a major role in the EB of this system.[2,3] However, all the studies have aimed to the stably oxidized Fe nanoparticles. The effect of the FIM thickness on the EB in this system has been neglected. In this study, a controlled oxidizing procedure was adopted to obtain Fe/Fe 3 O 4 nanoparticles with different Fe 3 O 4 thickness. The Fe 3 O 4 thickness dependence of the EB was studied.

Metamagnetism, a sudden increase in the magnetization of a material with a small change of external magnetic field, are calling more attentions because of their rich magnetic phenomena and scientific significance [1][2]. There are quite different physical causes for different types of metamag-nets. In this work, metamagnetism has been found in arc-melting Sm(Ni 0.5 Fe 0.4 Cu 0.1 ) 7 . The physical property measurement system (PPMS) is used to measure the magnetic properties. The hysteresis loops at different temperatures (T>5K) are shown in Fig.1. Both sides of the hysteresis loops exhibit obvious metamagnetic behaviors. The hysteresis loops show wasp-waisted character. At the beginning of the curves the magnetization increases rapidly and then gets saturation at about 1T. When field increases continuously to the critical magnetic fields (H cm ) metamagnetic behavior appears. The lower the temperature is, the higher the H cm is. The magnetization appears to saturate when field increases to a higher value. The magnetization stays at high magnetization state until the field decreases to about 1T. The magnetizatic behaviors at another side of the hysteresis loops are the same. The critical magnetic fields (H cm ) corresponding to the metamagnetic points increases with the temperature decreasing by an exponential dependence (see Fig.1 inset). The spin reverse model with thermal activation (TA) is used to explain the relation of the critical field to temperature. The expression can be written as H cm (T)=H cm (0)exp(−kT/U), where Hcm(T) is the critical field at T, H cm (0) is the calculated value at 0K, k is the Boltzmann constant, U is the energy needed to turnover one spin [3]. The fitting results show U≈6.6×10−15 erg. At temperatures, below 5K, the smooth jumps turn into step-like jumps (see Fig.2). The number of the steps and the values of critical fields vary with different samples. The inset in Fig.2 is the enlargement of one step with a field interval of 0.05T. When repeating the magnetization process, the hysteresis loops can coincide compactly, which is different from the usual Barkhausen jumps [4]. The XRD results show that the main phase is hexagonal P6/mmm structure and the easy magnetization direction at room temperature is along c axis, which may show high anisotropy constants, where macroscopic quantum tunneling (MQT) may happen [5][6][7]. As temperature gets extremely low, the thermal activation can be ignored and the quantum behavior becomes obvious. One possible explanation is as follows: the MQT happens first, which leads to a release of thermal energy and increase of sample temperature, followed by a huge magnetization reversal due to the external magnetic field. A step-like magnetic jump appears. The differences of step numbers and H cm values between different polycrystalline samples are thought to be related to the relative orientation of the crystalline grain and the field direction. It seems that the MQT and TA models have solved the problem well. Another possible explanation is the narrow domain-wall pinning, but such a mechanism would have difficulty accounting for the presence of multistep jumps and the transition from one smooth jump to several sharp jumps just by changing few kelvins.

With the assistance of a kind of photonic Robin Hood that is originated from four-wave mixing in a dispersion-flattened high-nonlinearity photonic-crystal fibre, a novel dual-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated by using a sampled fibre Bragg grating. The experiments show that, due to the contribution of the photonic Robin Hood, the proposed fibre laser has the advantage of excellent uniformity, high stability and stable operation at room temperature. Our dual-wavelength EDF laser has the unique merit that the wavelength spacing remains unchanged when tuning the two wavelengths of laser, and this laser is simpler and more stable than the laser reported by Liu et al. [Opt. Express, 13 142 (2005)].

A kind of photonic 'Robin Hood' based on four-wave mixing is proposed and proved to be effective, theoretically and experimentally, in detail. Its applications for L-band dual-wavelength erbium-doped fibre (EDF) laser use are experimentally demonstrated at room temperature. The experimental results show that the conventional EDF cavity only induces a very unstable L-band laser, but the novel Robin Hood can effectively suppress the homogeneous gain in the erbium laser. By using suitable fibre Bragg gratings and stretching them, the proposed EDF laser can operate from ~1520 to ~1635 nm, so our dual-wavelength EDF laser can be used in lasing operation not only for the L band but also for the C band. The outstanding merits of our dual-wavelength laser are the flexible tuning and the ultrabroad spectral range of more than 115 nm. The experimental results show that the stability and uniformity of the proposed dual-wavelength laser in C-band operation are better than those for the same laser in L-band operation.

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

The optical properties and potential applications of four kinds of fulgide and fulgimide were studied. A parallel optical storage apparatus was set up, which could reach the area density of 4.8 × 107 bits/cm2 on the fulgide/PMMA film. Fourier transform orthogonal circular polarization holographic data storage was performed with high signal-to-noise-ratio reconstruction image, which obtained the storage density of 2 × 108 bits/cm2 for single hologram. Two-photon induced micro-patterns were recorded on the fulgimide/PMMA film with 800 nm, 100 fs, 1 KHz, 50 mW femtosecond laser. Dual-wavelength (650 nm and 488 nm) optical images storage were tested on a two-color mixing fulgides/PMMA film.

Three-dimensional optical recording of high contrast spherical bits (diameter

BR-D96N is a kind of genetically site-specific mutant of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose there are three main states in the photochromic process, i.e. B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from measuring the absorption dynamics at 407 nm and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis.

A simple folded-cavity used for intracavity frequency-doubled Nd:YVO4 laser was analyzed by transmission matrix and numerical calculation. We have selected a set of proper cavity parameters which can be used readily by operating at high power levels with low threshold, high e:ciency, and wide dynamic operating range. 5.6-W TEM 00 green laser has been obtained at a 22-W pumping power and with an optical–optical conversion e:ciency of 25.5%. ? 2002 Elsevier Science Ltd. All rights reserved.

The multi-peak spectrum of Ti:sapphire pulses observed experimentally under ultra-broad bandwidth conditions (< 15 fs pulse length) has been explained theoretically. It is shown that the self-phase-modulation effect is equivalent to the process of degenerate four-wave frequency-mixing. Based on this theoretical underpinning, the presence or absence of a multipeak spectrum provides a practical measure of whether the intracavity group-velocity-dispersion is ideally compensated for or not.

An Ytterbium-doped mode-locked fiber laser using the polarization sensitive isolator and polarization controllers (PC) is reported. In the normal dispersion, the fiber laser can oscillate at the multi-pulse states by adjusting the position of the PC. On the condition that the polarization state isn’t changed, the outputs of Ytterbium-doped mode-locked fiber laser change from single pulse to multi-pulse by increasing the pump power. The fiber laser can achieve different multi-pulse output by adjusting the PC1 and PC2 carefully.

The optical storage characteristics of a new kind of organic photochromic material—pyrrylfulgide were experimentally investigated in the established parallel optical data storage system. Using the pyrrylfulgide/PMMA film as a photon-mode recording medium, micro-images and encoded binary digital data were recorded, readout and erased in this parallel system. The storage density currently reaches 3xl07bit/cm2. The recorded information on the film can be kept for years in darkness at room temperature.

International audience; Ultrashort pulsed laser photoinscription of Ti:Sapphire crystals may result in the self-organization of nanoscale material redistribution regions in regular patterns within the laser trace and stress-induced birefringence around the laser trace. We report on the formation of anisotropic optical waveguides in Ti:Sapphire by a procedure that involves femtosecond laser inscription of adjacent nonguiding birefringent traces with nanopatterned crosssections and the accumulation of stress birefringence in the region between. Double parallel line structures with a separation of 25μm with vertical and horizontal nanoscale arrangements were written with a choice of orthogonal polarizations. Due to anisotropic light scattering on periodic nanostructures and stress-induced birefringence in the central zone, remarkable polarization dependent guiding effects were observed as a function of the microscopic geometry of the structures. Building on this polarization sensitivity, several structure such as 3 × 3 waveguide arrays, diamond and hexagon patterns are also investigated.

A passively Q-switched ytterbium-doped double-clad fiber laser with SESAM as a saturable absorber is demonstrated experimentally. This system showed up to 18.7mW output power, up to 29.4 kHz repetition rate, a maximum pulse energy of 0.636μJ and a minimum pulse duration of 3.148 μs. The characteristics of pulse were investigated, and the theoretical analysis agree well with the experimental results.

This paper describes characteristics of a short pulse doped rare earth fiber laser and amplifier. We have obtained very stable pico-second and femto-second laser pulses from fiber laser. An all-fiber laser and amplifier of a double-clad fiber are researched in detail. The pulse of 177fs at wavelength of ~1.50um has been got from fiber laser. The energy of single pulse of 153μJ has been obtained after an amplifier of a double-clad fiber at repetition-rate of 30 KHz.

The structure and magnetic properties of MnCoSi1− x Px (x = 0.05–0.50) are systematically investigated. With P content increasing, the lattice parameter a increases monotonically while both b and c decrease. At the same time, the temperature of metamagnetic transition from a low-temperature non-collinear ferromagnetic state to a high-temperature ferromagnetic state decreases and a new magnetic transition from a higher-magnetization ferromagnetic state to a lower-magnetization ferromagnetic state is observed in each of these compounds for the first time. This is explained by the changes of crystal structure and distance between Mn and Si atoms with the increase of temperature according to the high-temperature XRD result. The metamagnetic transition is found to be a second-order magnetic transition accompanied by a low inversed magnetocaloric effect (1.0 Jkg−1K−1 at 5 T) with a large temperature span (190 K at 5 T) compared with the scenario of MnCoSi. The changes in the order of metamagnetic transition and structure make P-doped MoCoSi compounds good candidates for the study of magnetoelastic coupling and the modulation of magnetic phase transition.

By suppressing the growth of impurities, a melt spinning method was successfully applied to the synthesis of typical layered CeMn2Si2 and AlFe2B2 compounds. X-ray diffraction analysis showed that CeMn2Si2 and AlFe2B2 had good purity and crystallized in ThCr2Si2- and AlFe2B2-type structures, respectively. The differences among three -type structures were also analyzed. The magnetic properties were investigated by magnetic measurements and electronic structure calculations. It was found that the Fe moment of AlFe2B2 reaches 1.32 μB at 5 K, which fits well with the calculated result of 1.44 μB at 0 K, and that the isothermal magnetic entropy change reaches 7.2 J kg−1 K−1 at 5 T, which shows great potential for room-temperature refrigeration applications.

We report on an experimental investigation into the recording and readout of 3D high-density optical data storage in transparent optical glasses using a femtosecond laser. A compact Ti:sapphire ultrafast laser amplifier as writing laser was developed to output 100mW 2.1ps at 1KHz with 1W pump laser. Laser pulses modulation is realized by modulating two circuits of trigger pulses signal which are used to control laser pulses trapping and switching out from cavity, respectively. A formatted and coded writing was realized in fused silica and doped polymethylmethacrylate(PMMA) bulk. A phase-contrast and a reflection confocal reading system with software are developed for optical readout of multi-layer data bits in parallel.

Based on the physical mechanisms of femtosecond laser-transparent materials interactions, three kinds of micromachining including three dimensional data storage, optical waveguide network and grating with an amplified Ti:sapphire laser system are presented. These optical devices on different transparent materials by femtosecond pulses are featured. The effect of laser machined parameters such as irradiated energy, the scanning speed and the recording material upon fabricated optical devices is studied in detail. From examples, the versatility of femtosecond laser precise micromachining technique is demonstrated. Practical application of femtosecond laser materials processing is illuminated.

A high power double-clad ytterbium-doped large-mode-area photonic crystal fibre (LMA PCF) laser was demonstrated using a unique Fabry-Perot (F-P) configuration. A Continuous-wave output power of 50 W at ~1.04 μm with a slope efficiency of 76.3% was obtained. Single transverse mode operation is achieved without any thermal-optical problems. This laser has the potential for scaling to much higher output power.

We present for the first time, to the best of our knowledge, active waveguide device and array in E/ + -Yb 3+ codoped lithium silicate glass directly written by near-IR femtosecond laser pulses. We show that in Er 3+ -Yb 3+ codoped lithium silicate cylinder waveguide of diameter 4um is produced by use of a microscope objective with a numerical aperture of NA=0.1 and laser pulse of 400fs duration with a energy of 3 μ J generated by a Ti:sapphire amplifier. The sample could be translated parallel to the laser beam axis by a computer-controlled three-dimensional translation stage. We analyze its guided wave characterization. This one-step process provides a simple and flexible method for the fabrication of integrated optics components.

Darkening and micro-explosions inside ZBaF15 optical glass are investigated by using focused femtosecond laser pulse. With loose focusing, multiple micro-explosions occur in fused silica and ZBaF15 optical glass with single femtosecond pulse. The micro-explosions driven in the center of darkening region are observed in ZBaF15 optical glass. A numerical simulation is given by a model based on the beam propagation in wave-guide channeling induced by the front of excitation pulse. The mechanism of refractive index modification, which induced by femtosecond pulse, is discussed.

Photoinduced anisotropic properties of pyrrylfulgide are studied. From measurement of the photoinduced spectrum of dichroism, the birefringence spectrum is evaluated by Kramers-Kronig relations. At optimal exposure of 13 ~ 20J/cm 2 a maximum photoinduced dichroism ( D perpendicular - D parallel ) of about 0.1 and a maximum photoinduced birefringence ( n perpendicular - n parallel ) of about 8×10 -4 are achieved. We exploit this photoinduced anisotropy and use a pyrrylfulgide/PMMA film to demonstrate optical image processing such as contrast reversal, image subtraction and summation, low-pass filtering and edge-enhancement. From the spectra of dichroism and birefringence the spectrum of the diffraction efficiency for polarization holography is calculated. We demonstrate that diffracted images with high signal-to-noise-ratio (SNR) can be obtained by holographic recording with orthogonal polarization.

Three-dimensional optical data storage realized by microexplosion based on a multi-photon absorption process is a promising method to fabricate optical read-only memory with large recording capacity. The writing of multi-layered data bits inside a PMMA block doped with rare-earth ions (Sm 3+ and Ce 3+ ) under multi-photon absorption excited by a 800nm femtosecond (fs) pulsed laser was reported. The fs pulsed laser beam was focused into the sample with a microscope objective (N.A.= 0.65 40X), and bits were recorded as structurally altered regions which have high contrast in refraction index and fluorescence intensity. The recorded bits could be retrieved parallel by transmission using a conventional optical microscope or be read out serially by fluorescence signal of the structurally altered region excited by a 514.5nm laser using a reflect-type confocal microscope. Experimental results of three-dimensional recording and reading with 4-um in-plane bit spacing and 8-um inter-plane spacing in eight layers were presented. The structure changed in the material before and after the laser irradiation was discussed.

Using Fourier-transform holographic setup a storage density of 2×108 bits/cm2 was obtained in an optical film containing the genetic variant bacteriorhodopsin BR-D96N by the orthogonal circular polarization of recording.

A new and more-flexible and directly femtosecond laser writing technique for the fabrication of waveguides has been demonstrated. By using this avenue, waveguides of 5mm are produced, and their characters are discussed. At the same time, the two writing manners are compared and the related physical mechanisms are summarized in detail.

The experimental results of erbium-ytterbium co-doped double-cladding fiber lasers (EYDCFLs) are reported. The output powers as functions of the input pump power, and the reflectivity of the cavity mirror are described. The maximum output power is about 733 mW, with a slope efficiency of about 30% and optical to optical conversion efficiency of 25.3 %. Numerical analysis of this EYDCFL was also performed based on the rate and propagation equations. The calculated output powers of 1.492 W and conversion efficiency of 51.4 % are doubled than the experimental results. That means further improvements could be made by optimum design of the laser, such as well cutting the fiber-end, adding dichroic mirror at the output end, or making fiber Bragg gratings directly in the fiber core.

CD-RW is restricted by the size of material particles, the conduction of heat, etc. Besides, the recording speed is seriouslylimited by the process of heating. Photonic materials and parallel method will be the trend in the optical data storage.Because it is based on the photon reaction on the molecule scale, the storage density and speed will be greatly increased.in this paper, a new kind of organic photochromic material — pyrrylfulgide was studied. A parallel optical data storagesystem was established. Using the pyrrylfulgide/PMMA film as a recording medium, micro-images and binary digitalinformation could be recorded, readout and erased in this parallel system. The recorded information on the film can bekept for at least 8 months in dark at room temperature. So far, the storage density is 3x 1 O bit/cm2.Key words: pyrrylfulgide, photochromism, optical data storage

Pyrrylfulgide was used as rewritable holographic recording medium. He -Ne laser was used to write holograms and UV light was used to erase holograms. Co -polarized and cross-polarized holographic gratings were r espectively recorded and reconstruction images were retrieved. Using conjugated wave of reference beam as reconstruction beam, image aberration could be corrected.

The photochromic retinal protein bacteriorhodopsin (BR) modified by genetic method is considered as a promising material for optical and holographic recording because of its effective photochemistry, high stability and unique reversibility. The parallel image recording can largely increase the speed of data writing and reading in comparison with the bit-type recording. Here, we established a micro-imaging system with BR-D96N biofilm as recording medium. The optical image loaded on a LCSLM was illuminated by an argon laser (514 nm) and was micro-imaged on the BR film with a high resolution lens. The BR film was mounted in a two dimensional micropositioning system for accurately addressing. The recorded images were readout by a CCD camera under weak illumination of 514 nm laser. In this system, we can record 1000 frames of microimages on the BR film with each frame having an area of 460μm × 350μm. This system can be developed into a two dimensional parallel digital optical data storage setup.

With cascade oscillation scheme from level 5I6,to 5I7, to 5I8 in Ho3+: ZBLAN fiber laser, it not only can produce cW 3- and 2- ?m laser beams simultaneously from one oscillator with appropriate pumping source, but also improves the output power and efficiency. In this paper, the operation principles of 3- and 2- ?m cascade Ho3+: ZBLAN fiber laser is analyzed. Both dynamic and steady state rate equations of this laser pumped with1.1-?m band laser are given for the first time. Basic designs of this laser pumped by Ytterbium-doped double clad fiber lasers (YDCFL) are given. Based on the theoretical analysis and designs, numerical computations of the steady state rate equations were performed. The numerical solutions agree well with the experimental results.

The increasing capacity of wavelength-division multiplexing (WDM) transmission systems requires higher output power of erbium doped fiber amplifiers (EDFAs). The two improvements are the use of double cladding fibers (DCF) and the addition of ytterbium oxide as co-dopant in the glass base. In this paper, the operation principles of double-cladding erbium-ytterbium co-doped fiber amplifiers were analyzed. Numerical analysis of erbium-ytterbium co-doped DCF amplifiers using EY801 fiber manufactured by INO, Canada has been performed based on the rate and propagation equations. The maximum output power as functions of the fiber length, the input pump power, the erbium-ytterbium concentration and pumping ways were described. The results show that the ideal erbium-ytterbium co-doped DCF amplifier with EY801 fiber is that with the fiber length of about 62 meters, with as higher as possible pumping powers, and with doubled-ended pumping configuration.

Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.