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This paper focuses on the feasibility of fast neutron energy spectrum measurement. The MCNPX and Geant4 are used to simulate two conversion models of stacking neutrons to protons in the triple GEM cathode coupled with multilayer polyethylene, with five kinds of single-energy neutron sources and Am-Be continuous neutron sources taken as research objects. The response function to 160 single energy neutrons and the recoil proton spectrum distribution of the above sources of the detection system are obtained by simulation. Using GRAVEL algorithm and MLEM algorithm and through simulation, the recoil proton spectra of six kinds of fast neutron sources are obtained, and they are further analyzed. The spectrum outcome is compared with the standard input spectrum, showing that they are in good agreement with each other. The relative uncertainty of the unfolding spectrum is around 10%–15%. In this part the relation of gas detector with the precision of unfolding spectrum is also discussed. The result shows that when the energy resolution of micro-pattern gas detection is better than 30%, the accuracy of fast neutron spectrum can meet the needs of practical applications. Furthermore, a new transformation model is proposed based on previous experiments and proves the feasibility of applying micro-pattern gas detector to fast neutron detection of simulation. Moreover, spectrum reconstruction can be achieved by using the obtained recoil proton spectrum combined with a suitable inversion algorithm. The modeling and spectrum analysis of this study can provide a different method of applying the fast neutron detection system composed of micro-pattern gas detectors to the detection of unknown fast neutron sources and also to the source recognition through spectrum reconstruction.

Currently, low-dimensional materials are a hot spot in the field of thermoelectric research, because the thermoelectric properties will be significantly improved after the low-dimensionalization of bulk materials. In a bulk material, its thermoelectric figure of merit ZT value cannot be increased by changing a single parameter, because the parameters of the material are interrelated to each other, which is not conducive to the research of internal factors and thus limiting the efficiency of thermoelectric material, but thermoelectric material on a micro-nano scale is more flexible to adjust its thermoelectric figure of merit ZT value. There are many different kinds of methods of implementing the low-dimensionalization of bulk materials. In this paper, size-controllable Si micro/nanobelts are prepared based on semiconductor micromachining and focused ion beam (FIB) technology, and the thermoelectric properties of Si micro/nanobelts of different sizes are comprehensively studied by the micro-suspension structure method.In this experiment, we find that the conductivity of doped Si micro/nanobelt is significantly better than that of bulk Si material, that as the width of the Si micro/nanobelt decreases, the thermal conductivity of the material decreases significantly, from 148 W/(m·K) of bulk silicon to 17.75 W/(m·K) of 800 nm wide Si micro-nanobelt, that the Seebeck coefficient of the material is lower than that of the corresponding bulkmaterials. The decrease of thermal conductivity is mainly due to the boundary effect caused by the size reduction, which leads the phonon boundary scattering to increase, and thus significantly inhibiting the behavior of phonon transmission in the Si material, thereby further affecting the transmission and conversion of thermal energy in the material. At 373 K, the maximum ZT value of the 800 nm wide Si micro/nanobelt reaches ～0.056, which is about 6 times larger than that of bulk silicon. And as the width of the Si micronanobelt is further reduced, the thermoelectric figure of merit ZT value will be further improved, making Si material an effective thermoelectric material. The FIB processing technology provides a new preparation scheme for improving the thermoelectric performances of Si materials in the future, and this manufacturing technology can also be applied to the low-dimensional preparation of other materials.

This paper analyzes the reason why the polymer is melted on a non-forming surface during ultrasonic embossing and proposes a method to inhibit the polymer melting.On the basis of the heating mechanism of ultrasonic,it points out that the polymer melting phenomenon on non-forming surface is resulted by the friction in a horn-substrate interface.Then,it proposed the method"two interfaces of different friction coefficients"to inhibit the polymer melting and implemented the method by coatings surface protection films on the non-forming surface.To optimize the protection films,and the influences of the four coating film conditions on the softening time are examined through Taguchi method.The results show that the Sekisui#622E-50 film shortens the softening time by 3.4sandthe Sekisui#622WB film reduces the softening time error by 0.64 s.It demonstrates that surface protection films coated can avoid polymer melting on the non-forming surface,and improve the process replication ability and the process stability in ultrasonic embossing.

A thermal-assisted ultrasonic embossing method was proposed based on silicon molds to replicate thermoplastic substrates in a low cost and high efficiency.The ultrasonic vibration was applied to the mold-polymer interface to heat the polymer rapidly to the embossing temperature.To reduce the risk of damaging the mold,the die was preheated to a temperature which is 35-50℃ below the glass transition temperature(Tg)of the polymer.Then,the influences of the ultrasonic amplitude, ultrasonic force,ultrasonic time,and the thermal-assisted temperature were studied by orthogonal array experiments to reveal the mechanism of ultrasonic embossing.The influence of the substrate thickness was also investigated.The experimental results show that the most important parameter for replication is the thermal-assisted temperature,follows by the ultrasonic amplitude.Moreover,the ultrasonic force is the most important parameter for replication uniformity,while the thinner polymersheets are more conducive to be replicated under the same circumstances.With the optimized parameters,the replication accuracy has reached 99%on a Polymethyl Methacrylate(PMMA)substrate,and the cycle time is less than 50s.All theses studied show that thermal assisted ultrasonic embossing has high replication efficiency and is a potential way to mass formation of polymer microstructures.

The surface of TiO2 inverse opal material was modified by Liquid Phase Deposition(LPD) method, and a layer of TiO2 nanoparticles was deposited on the inverse opal framework in order to increase the specific surface area. The photo-catalytical degradation of Rhodamine B was used as the probe-reaction to investigate the photocatalysis ac- tivity of the TiO2 inverse opal membranes, and the influences of boric acid concentration of the LPD solution on surface morphology and photocatalysis activity of TiO2 inverse opal membranes were investigated. The results showed that the photocatalysis activity of TiO2 inverse opal membrane modified by LPD method was improved which was about 6 times higher than that of the unmodified TiO2 inverse opal when the boric acid concentration of PLD solution was 0.0183 g/mL.

The carrier transport and recombination in light-emitting diodes(LEDs) determine the non-uniform intensity and distribution of the internal heat source.The non-uniform temperature field also influences the carrier transport and recombination in LEDs.Thus the carrier transport and recombination are strongly coupled with temperatures.In this paper,the internal quantum efficiency,spectrum characteristic and photoelectric conversion efficiency of LEDs with substrates of sapphire,Si and SiC are systematically studied by a non-isothermal multi-physics-field coupling model.It is shown that the LED with SiC substrate has the smallest efficiency droop effect and exhibits the highest spectrum intensity and photoelectric conversion efficiency,among the LEDs with substrates of sapphire,Si and SiC.This is because the LED with the substrate of SiC has the best thermal dissipation capability,thus the non-uniform temperature field has the smallest effect on the carrier transport and recombination,leading to the significantly enhanced carrier concentration in the active region and decreased current leakage.

The slippage between discs and rail is one of important factors for the measurement accuracy of an involute.However,control of frictions effectively can modify the slippage of discs.In the paper,frictions between discs and rail are analyzed respectively when a cord and a belt are used to drive the discs to roll.According to the analysis and experiment,it shows that if measuring forces are 0.7 N and 0.2 N and the base discs is drived by the cord and belt,frictions are 0.02 N and 0.07 N respectively,for the base disc clockwise rolled;where the effect of the slippages of based discs on the involute measurement can be ignored.Moreover,the slippage can also be reduced by increasing the weight of base disc groups,and measurement difference of involute is 0.06 μm when the rolling directions of the base discs are different.

In order to improve the efficiency of ultrasonic bonding process for a polymer Electro-Mechanical System(MEMS) and to prevent the flow of polymer under a high temperature,a micro energy director array was proposed.Based on the experiment of PMMA micro-pipe sealing,the influence of micro energy director array on the process of ultrasonic sealing was studied.Five kinds of micro energy directors with different heights were fabricated on the sealing surface by a hot embossing technique.The method of ultrasonic precise sealing based on acoustic transfer efficiency feedback was used in the experiment to study the influence of the height of the micro-array structure on the quality of ultrasonic sealing and to observe the wetting behavior of micro-array structure.Experimental results indicate that the ultrasonic energy to achieve complete connection increases with increasing the height of micro energy director array.The micro energy director can control the flow of the melting-polymer effectively and can obtain the uniform sealing surface and high quality precise sealing.

PurposeThe purpose of this paper is to provide some useful information on the tribological performance of thermoplastic polyimide (TPI) reinforced with rigid glass fillers of different shapes and sizes under dry, water, and oil lubrication conditions.Design/methodology/approachRigid glass fillers of different shapes and sizes are chosen to modify TPI and its mechanical properties are measured. The stress‐strain behaviors of the composites are simulated by the finite element method and the effect of filler morphology is also considered. Furthermore, the tribological performance of the composites is investigated in different environmental media, including air, water, and oil.FindingsIt is demonstrated that the toughness of the materials decreases on filling them with rigid glass, and that stress concentration causes cracks around the spherical glass beads, which reduces the material impact strength. Owing to heat moulding technology, glass fiber has certain orientation and absorbs the impact energy effectively. A better wear‐resistant material is obtained by choosing a bigger filler due to its higher bond strength with the matrix. Under water and oil lubrication, the fatigue failure is the main reason for material wear, and fiber‐reinforced TPI has favorable wear‐resistance due to its shape. Meanwhile, glass beads could roll on the contact surface, which polishes the surface and reduces the friction coefficient, and its effect is reduced on oil lubrication for its high viscosity.Originality/valueThis paper analyzes the effect of rigid glass fillers of different shapes and sizes on the mechanical properties and tribological performance of polyimide composites.

PurposeTo provide some useful information on tribology performances of molybdenum disulfide (MoS2) reinforced thermoplastic polymide under dry and water lubrication conditions.Design/methodology/approachThe effect of MoS2 content on composites' mechanical and tribological performances was investigated and worn morphologies, elements distribution and wear mechanisms under dry and water lubricant condition were also analyzed.FindingsAs a result, the composites' main mechanical performances decreased partly compared with pure PI and it became more stable with MoS2 content unceasingly increasing (up to 20 wt%). In the dry sliding condition, the friction coefficient decreased obviously by filling MoS2. The wear of composites which filled 10‐15 wt% MoS2 was less than other composites in which MoS2 content was below to 5 wt% or high than 20 wt%. It was found that materials wear happened mainly at initial stages of tribology test which the temperature was so high and the adhesive wear had a dominant place during the test process. While in the water lubrication condition, the composites tribological performances were improved evidently and MoS2 was still an effective lubricant and the fatigue wear was the main factor during the tribology process.Originality/valueThe paper analyzed the MoS2's effect on materials mechanical and tribological performances and divided the tribology process into two parts according to materials friction and wear.

Visual experiments were conducted to observe droplet oscillation on horizontal surfaces with air flow. The different Cu test surfaces were polished with different grit sandpapers. Two liquid drop oscillation modes, forward-backward and upward-downward, were visually observed in the experiments. Additionally these two modes were observed to transition from one to another under some conditions. The results indicate that the oscillating characteristics were closely dependent on surface roundness, droplet size, and air flow velocity. A larger radius and higher air speed would decrease the oscillation frequency, while the frequency would initially decrease and then increase as the roughness changed from the smooth to rough plates. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(1): 13–19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20098

A supercontinuum extending from 350 nm to more than 1700 nm is generated in microstructured fibre (MF) with randomly distributed air holes in cladding and core by using 15-fs pulses of a 790-nm laser. The maximum total power of the supercontinuum is 63 mW with 288 mW pump power from a 100× microscope objective. The wavelength and power of visible light ranging in the supercontinuum can be tuned by adjusting the input end of random the MF (to change pump incident point or incident angle). In particular, white light has been observed. The polarization states and waveguide modes of the visible light change with adjustment of the pump incident point or incident angle.

A model of two-region structure of a nucleus is proposed to describe nucleus evolution. The interfacial tension between bulk liquid phase and nucleus is dependent on the density gradient in the transition region and varies with the structure change of the transition region. With the interfacial tension calculated using this model, the predicted nucleation rate is very close to the experimental measurement. Furthermore, this model and associated analysis provide solid theoretical evidence to clarify the definition of nucleation rate and understand the nucleation phenomenon with insight into the physical nature.

Anatase TiO2nanosheet porous films were prepared by calcination of the orthorhombic titanic acid films at 400°C. They showed an excellent photocatalytic activity for CO2photoreduction to methane, which should be related to their special porous structure and large Brunauer-Emmett-Teller (BET) surface area. In order to further improve the photocatalytic activity, Pt nanoparticles were loaded uniformly with the average size of 3-4 nm on TiO2porous films by the photoreduction method. It was found that the loading of Pt expanded the light absorption ability of the porous film and improved the transformation efficiency of CO2to methane. The conversion yield of CO2to methane on Pt/TiO2film reached 20.51 ppm/h·cm2. The Pt/TiO2nanosheet porous film was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Moreover, the transient photocurrent-time curves showed that the Pt/TiO2nanosheet porous film exhibited higher photocurrent, indicating that the higher separation efficiency of the photogenerated charge carriers was achieved.

Graphene has been a superstar in the fields ranging from materials science to condensed-matter physics since 2004. Graphene possesses good thermal and mechanical properties, high electron transfer capability and relatively low production cost. As a consequence, graphene has been used in the areas of multi-functional advanced materials and electronics. A direct disperse method has been widely applied to polymers to improve their dielectric properties. Recently, graphene/polymer composites have received much attention. Graphene nanosheets can significantly improve the physical properties of the host polymer at a very low content of conductive filler loading. Poly vinylidene fluoride (PVDF) is a semicrystalline thermoplastic polymer with remarkably high piezo-/pyroelectric coefficient, and excellent thermal stability and chemical resistance. More efforts have been recently devoted to the preparations of high-' composites based on PVDF. In this work, a graphene/PVA/PVDF nanocomposite film composed of poly(vinyl alcohol) (PVA), reduced graphene oxide (RGO), and poly (vinylidene fluoride) (PVDF) is fabricated. First of all, graphene oxide (GO) is prepared by the modified Hummers method. GO and PVA are successively dissolved in the dimethyl sulfoxide (DMSO) solution, in order to obtain PVA functionalized GO which is formed via non-covalent bonds. Then PVDF is added into this solution to form a homogeneous three-phase aqueous mixture. According to the solution-casting and thermal reduction processes, the three-phase nanocomposite films are formed. The thickness values of the films are in a range of 0.3-0.4 mm. The square specimens are coated with a silver paste prior to electrical measurements. The obtained products are characterized using X-ray diffraction, UV Vis absorption spectrum, Fourier transform infrared absorption spectrum, and atomic force microscopy. The morphologies of PVDF and RGO/PVA/PVDF films are investigated by a scanning electron microscope. Electrical measurements are conducted in a frequency range from 102 to 104 Hz. Results suggest that GO can be reduced to RGO and phase transition of PVDF from to phases is effectively promoted at 120 ℃. The dielectric properties of the polymer matrix are improved. Furthermore, PVA modified RGO is easier to disperse in the PVDF substrate than the original one, which strongly reduces the spherulite size of PVDF and improves the dielectric property of the composite film. The percolation threshold (fvol*) of RGO/PVA/PVDF film is estimated to be 8.45 vol.%, and the dielectric constant of the film is 238 times as large as that of the pure PVDF films at 102 Hz. In addition, the dielectric constant increases rapidly near the percolation threshold and depends on frequency, which is mainly ascribed to the Maxwell-Wagner-Sillars polarization in the low frequency range. This study provides a low-cost and simple method of preparing polymer nanocomposites with high dielectric properties.

A self-organized In0.5Ga0.5As/GaAs quantum island structure emitting at 1.35 mum at room temperature has been successfully fabricated by molecular beam epitaxy via cycled (InAs)(1)/GaAs)(1)monolayer deposition method. The photoluminescence measurement shows that a very narrow linewidth of 19.2 meV at 300 K has been reached for the first time, indicating effective suppression of inhomogeneous broadening of optical emission from the In0.5Ga0.5As island structure due to indium segregation reduction by introducing an AlAs layer and the strain reduction by inserting an In0.2Ga0.8As layer overgrown on the top of islands. The mound-like morphology of the islands elongated along the [1 (1) over bar0] azimuth are observed by the atomic force microscopy measurement, which reveals the fact that strain in the islands is partially relaxed along the [1 (1) over bar0] direction. Our results present important information for the fabrication of 1.3 mum wavelength quantum dot devices.

Designed microtextured surfaces have shown promising applications in tuning the wettability of a liquid droplet on the surfaces and attracted great attention over the past decade; unfortunately, the effect of surface geometry on wetting properties is still poorly understood. In this work, two- and multi-stage pillar microtextures are designed to construct gradient surfaces by altering pillar width and spacing. Then, the multi-phase lattice-Boltzmann method (LBM) is used to investigate the wetting dynamics of a liquid droplet on the gradient surface. Results show that for the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis is found to be proportional to the roughness gradient when droplet/surface system is in the Cassie-Baxter state. However, this proportional relation is no longer correct when the system is in the transition state between the Wenzel and Cassie-Baxter states. For the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis always increases linearly with increasing roughness gradient. Results also show that when a larger droplet is placed on the multi-stage gradient surface, stronger droplet motion is observed due to the smaller contact angle hysteresis. The present LBM simulations provide a guideline for the design and manufacture of the microtextured surfaces to tune the droplet wettability and motion.

Accurate measurements of the binding energy spectrum and momentum distribution of argon are performed using the high resolution (ΔE = 1.4 eV, Δp = 0.1 a.u.) energy multichannel (e, 2e) spectrometer (θ1 = θ2 = 45°, = 0°-±30°) built recently in our laboratory. Detailed satellite structure of argon has been observed. Good agreement can be found between the experimental data and the theoretical calculations performed using Hartree-Fock method with the different basis sets and configuration interaction method.

High-energy ion emission from intense-ultrashort (30fs) laser-pulse- cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweiback's expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.

We demonstrate that the Mg-doping in barriers can partially screen the polarization fields of InGaN-based green light-emitting diodes. The photocurrent spectra show that the Mg-doping samples have smaller polarization fields and the blue shift of the peak with increasing current is observed. The reduction of polarization fields can be attributed to the screening of the impurity holes generated by the Mg atoms in the barriers. The efficiency droop is sensitive to the Mg-doping concentration in barriers, while the sample with Mg concentration of 5 × 1019 cm−3 exhibits the lowest efficiency degradation of 12.4% at a high injection current.

The filter made up of two gratings performs as a two-dimensional non-spatial filtering. This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer. Diffraction efficiency of a single grating is up to 78% in Bragg's condition, then a two-dimensional non-spatial filter, which consists of two volume Bragg gratings and a half-wave plate, enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%. The Bragg's condition and effect of polarisation on performances of the two-dimension filter are also discussed.

Complex microstructures of liquid-crystalline polymers in nonhomogenous shear flow are studied by element free Galerkin (EFG) method based on the micro-macro dualscale model. The dualscale model combines the orientational diffusion equation in microscale with the flow governing equations in macroscale. The EFG method which has the merits of high accuracy and good stability can ensure the reliability of the simulation results. One simple and five composite structures of liquid-crystalline polymers in nonhomogenous shear flow are predicted by studying the influences of Deborah number on microstructures of liquid-crystalline polymers in plane Poiseuille flow. It shows that the instabilities in the transition region of the composite structures can cause some defects.

In this paper the complex rheological behaviors of rod-like polymer solutions in plane Couette flow are studied using micro-macro simulation. The micro-macro model is described by Doi theory with local inhomogeneous fluid. The finite volume method is used to solve the conservation equation on the macroscopic level and the Smoluchowski equation on the microscopic level in the numerical simulation. The numerical results predict several plane flow modes including some typical plane modes and two new complicated modes. Furthermore, simulation results show that the rheological phase diagrams for solutions of rigid rod molecules are mainly dependent on the Deborah number, the concentration of solutions and molecular scale, and the varying Deborah number have great influence on some micro-properties of tumbling period and orientation angle of flow-aligning.

Gaussian distribution models of voltage wave form of magnetically insulated diode (MID) of TEMPⅡ accelerator and intense pulsed ion beam (IPIB) density near the MID focus region have been built according to the results of experiments. Interaction of IPIB with a double-layer aluminum target coated by a thin film of gold has been studied using Monte Carlo method. The spatial and temporal evolution of deposited energy is obtained, the states of deposited energy for the different gold thickness are discussed, and the enhanced adhesion at interfaces by IPIB is investigated.

The mechanism of polystyrene submicrospheres assembling in aqueous suspension was studied systemically. During the evaporation of solvent, the PS spheres were transported to the water-air inter-surface, where these spheres self-assemble into colloidal crystal through the capillary force between the particles at water-air interface. The wettability of the PS spheres at the water-air interface changes from complete wetting to partial wetting and finally to non-wetting with the evaporation of water, so that the contact angle between the PS spheres and water increases gradually. The experiment showed that only after the contact angle reached a critical value θ′critical, could the PS sphere-assembly occur. The critical value θ′critical obtained from the Wenzel equation was greater than the measured value θcritical＝22° because the surface of the PS colloidal crystal was “regularly” coarse. The change of the PS spheres at water-air interface from the hydrophilic to hydrophobic is essential for the PS spheres to assemble into colloidal crystals.

The electron backscatter diffraction technique (EBSD) has been used to measure the microstructure of reactive ion etched(RIE) Al and damascene Cu interconnects, including the grain size, grain orientation and grain boundary characteristics. Linewidths of Cu interconnects, as well as the anneal processes of Al and Cu interconnects impacting on the microstructures and causing the electromigration failure were analyzed.

We observed the characteristics of high energy nanosecond chirped pulse by spectral-resolved streak camera，which works well with energetic chirped pulse of nanosecond pulse duration. At the same time，it can monitor the alignment of grating compressor. The measurement results show that the pulse generated by PW demonstration facility is linearly chirped，verifying the compressibility of amplified nanosecond pulse.

Evaporation self-assembly method, which is used to assemble sub-micrometer polys tyrene microspheres, is presented in this paper. In this process the polystyrene microspheres are effectively assembled at the gas-liquid interface of suspensio n as moisture evaporates at fixed temperature. The scanning electron microscope shows that the three-dimensional colloidal assemblies have regular close-packed face-centered cubic structure. It was shown that the evaporation was blocked by the polystyrene colloid crystals growing at the gas-liquid interface, and the am ount of the polystyrene microspheres transferred to the colloid crystals from th e suspension in unit time increased with the area of the assemblies. High-qualit y polystyrene colloid crystals can be assembled when not changing or decreasing the phase concentration, whose changes can be controlled by adjusting the assemb ly area and the evaporation temperature.

Optical properties of Al0.9Ga0.1As/AlyGa1-yAs/GaAs/AlxGa1-xAs DBR with inhomogeneous graded interfaces has been investigated by using characteristic matrix method. The refractive index model and the analytic characteristic matrix of graded interfaces are obtained. The reflectance spectrum and the reflective phase shift are calculated for GaAs/Al0.9Ga0.1As DBR and graded interfaces DBR by using characteristic matrix method. The effect of graded interfaces on the optical properties of DBR is discussed. The result shows an extra graded phase matching layer must be added in front of the graded interfaces DBR to fulfil the conditions of phase matching at central wavelength. The accurate thickness of phase matching layer is calculated by optical thickness approximation method.

Based on the time dependent theory of random lasers, which was established via combining Maxwell equations with the rate equations of a four-level atomic system, the output intensity of lasing modes varying with the pump rate and area as well as the medium's size and shape is simulated for two-dimensional random media by use of the finite difference time domain method. Results show that the pump-rate dependence of the output intensity presents not only a threshold property, but also a saturation property, just like that of the lasing modes in conventional lasers. Based on the dependence of mode property on the medium's and pump's parameters, the mode-selection approaches are proposed for two-dimensional random lasers, which are quite different from those performed in conventional lasers.

Laser pulse durations are dominated by the spectral bandwidths in chirped pulse amplification systems.Therefore,gain narrowing during amplification is one of the most important factors that limits the minimal pulse durations of compressed pulses in high_power ultrashort_pulse laser systems.The gain narrowing can be compensated by applying an acousto_optic programmable dispersive filter(AOPDF) to the laser system.Here we present the experiments and results with an AOPDF for the 200_TW Ti:sapphire laser.The spectral bandwidth is increased from the original 27?nm to 44?nm.The pulse duration correspondingly is decreased from 60?fs to 30?fs and thus the output pulse power is doubled.

Three-dimensionally ordered macroporous polystyrene was successfully synthesized through using silica sphere colloid crystals as template and in-situ polymeriza tion of styrene inside the template. The silica spheres with a diameter of 330 n m and 2.75% relative standard deviation were prepared by seeding method. For th e purpose of improving the wetting ability between the silica particles and styr ene, the hydrophilic surface of silica particles was switched to hydrophobic by 3-Aminopropyl-triethoxysilan (APS). Three-dimensionally ordered colloidal crystal was prepared by assembling the modified particles through a vertical depositio n technique at 30℃ for 48h. Styrene monomer was filled into the void of the tem plate and the polymerization of the styrene was carried out at 60℃ for 6h, being used (put the initiator in here) as initiator. The three-dimensionally ordered macroporous polystyrene was thus obtained by removing the silica template from polystyrene materials with 04% HF. The macroporous polystyrene shows a beautif ul iridescence in reflected light, which resulted from Bragg diffraction. SEM im ages indicated that the pores with a diameter of about 210nm were arrayed period ically and connected with each other.

InAs self-assembled quantum dots(QDs) covered by 3-nm-thick InxGa1-xAs(0 less than or equal tox less than or equal to0.3) capping layer have been grown on GaAs(100) substrate. Transmission electron microscopy shows that InGaAs layer reduces the strain in the InAs islands,and atomic force microscopy evidences the deposition of InGaAs on the top of InAs islands when x = 0.3.The significant redshift of the photoluminescence (PL) peak energy and the reduction of PL linewidth of InAs quantum dots covered by InGaAs are observed. In addition,InGaAs overgrowth layer suppresses the temperature sensitivity of PL peak energy. Based on our analysis, the strain-reduction and the size distribution of the InAs QDs are the main cause of the redshift and temperature insensitivity of the PL respectively.

A novel and more realistic calculation model and method for multipass laser pulse amplification has been put forward based upon the double side pumping scheme. We present here the systematic calculation and analysis on the amplification characteristics of the double side pumped confocal cavity Ti:sapphire amplifier and the chirped pulse multipass amplification through a new amplification configuration. Our experimental results show good agreement with the calculations. With such amplifier,the pass number is noticably reduced and some electro optical elements in regenerative amplifiers have been omitted.

Nanostructured titanium oxide films were deposited on silicon substrate via sol-gel dip coating method with tetrabutyl titanate as precursor. With reflective spectroscopic ellipsometry, the ellipsometric parameters Ψ and Δ of TiO2 films were measured. Then, with the Cauchy model, the ellipsometric data were fitted, and both the thickness and the optical constants at 380—800 nm wavelength of the films were obtained. A comparison was made between the reflectance of the films derived with the spectrophotometer and the simulated results. Meanwhile, the thickness of the films was calculated by interference method. Moreover, with the atomic force microscopy the surface microstructures of the films annealed at different temperatures were observed, and the relationship between the surface microstructures and optical constants of films was further discussed. The results showed that Cauchy model works well in describing the dispersion relationship of the TiO2 films, and the variation rules of optical constants （the refractive index, the extinction coefficient） with wavelength were obtained. The optical constants of the films were related with the microstructure. Those simulated reflectance spectrum accorded well with the measured result. And with a deviation of only 25%, the calculated value of the thickness was in accordance with which was obtained by spectroscopic ellipsometry.