Effects of pressure and gas-jet thickness on the generation of attosecond poulser

We investigate how the intensity and duration of an attosecond pulse generated from high-order harmonic generation are affected by the pressure and thickness of the gas jet by taking into account the macroscopic propagation of both fun- damental and harmonic fields. Our simulations show that, limited by the propagation effects, especially the absorption of harmonics, the intensity of an attosecond pulse cannot be improved by just independently increasing the gas pressure or the medium length. On the other hand, due to good phase-matching conditions, the duration of a generated attosecond pulse can be improved by changing the gas pressure.     

Fiber parametric oscillator for the 2 μm wavelength range based on narrowband optical parametric amplification

We describe a widely tunable synchronously pumped coherent source based on the process of narrowband parametric amplification in a dispersion-shifted fiber. Using an experimental fiber with a zero-dispersion wavelength of 1590 nm and pump wavelengths of 1530 to 1570 nm yields oscillations at 1970 to 2140 nm-the longest reported wavelength for a fiber parametric oscillator. The long-wavelength oscillations are accompanied by simultaneous short-wavelength oscillations at 1200 to 1290 nm. The parametric gain is coupled to stimulated Raman scattering. For parametric oscillations close to the Raman gain peak, the two gain processes must be discriminated from each other. We devised two configurations that achieve this discrimination: one is based on the exploitation of the difference in group delay between the wavelengths where Raman and parametric gain peak, and the other uses intracavity polarization tuning.     

Investigation of near-collinear degenerated quasi-phase matching optical parametric amplification using PPKTP crystal

The gain properties of near-collinear degenerated phase-matched optical parametric amplification (OPA) using PPKTP crystal are investigated theoretically. The results indicate that the type-0 phase matching of PPKTP has larger accepted angle and better gain spectrum by tuning crystal temperature or rotating crystal angle.     

Design and parametric amplification analysis of dispersion-flat photonic crystal fibers

In recent years, a new type of broadband amplifier, fiber optical parametric amplifier (FOPA) has been investi- gated, which utilizes four-wave mixing (FWM) to amplify the signals and offers a broadband amplification at arbi- trary wavelengths[1]. Though simple single-pump FOPA could offer a gain bandwidth of more than 200 nm, the gain spectrum is not flat over the amplifier bandwidth but has a difference as high as 15 dB between the lowest and the highest values, which brings to the diffi…     

Effects of inhomogeneous distribution of Si–Nc and Er ions on optical amplification in Si–Nc Er doped fiber

In this article, the effects of Si–Nc and Er³⁺ ions distribution parameters including inhomogeneous and homogeneous distribution profile are studied on the optical parameters such as gain, population inversion and Si–Nc induced losses. We have shown that by increasing of the concentration of Si–Nc particles the net gain and induced Si–Nc losses increased in homogeneous and inhomogeneous distributions. In practice, the homogeneous distribution of Er ions and Si–Nc is hard to be realized. Therefore, the inhomogeneous distributions of ions cased to perturb state in mode shape of optical signal then the investigations of those effects are important for high speed optical communications. In this article, a method for evaluation of the effects of inhomogeneous distribution of impurities on performance of optical amplifier is developed and the managing of the gain with use of suitable distribution functions is proposed.     

Effects of N-doping concentration on the electronic structure and optical properties of N-doped β-Ga2O3

The electronic structures and the optical properties of N-doped β-Ga2O3 with different N-doping concentrations are studied using the first-principles method.We find that the N substituting O（1） atom is the most stable structure for the smallest formation energy.After N-doping,the charge density distribution significantly changes,and the acceptor impurity level is introduced above the valence band and intersects with the Fermi level.The impurity absorption edges appear to shift toward longer wavelengths with an increase in N-doping concentration.The complex refractive index shows metallic characteristics in the N-doped β-Ga2O3.     

Optimizing the performance of TOAD by changing the wavelength and power of control pulse

The performance of terahertz optical asymmetric demultiplexer (TOAD) has been studied by modelling the semiconductor optical amplifier (SOA) in which the intraband effects had been taken into account. Numerical results are coincident with the experiment results. We interpret why there are three peaks in the switching window, which has never been reported before. In addition, we put forward the definition of the flatness of the switching window of TOAD for the first time By analysing the different phase of clockwise and counter clockwise signal pulse changed by SOA, appropriate peak power of control pulse and wavelength of signal and control pulse have been calculated in order to obtain large output power and flat switching window of TOAD.     

Measurement of the third order nonlinear optical coefficients of GaP and chirp parameter of laser pulse

The spectral resolved femtosecond pump-probe experiment is applied to measure the third order nonlinear refractive index coefficient, two-photon absorption coefficient of GaP crystal, and the chirp parameter of the input laser pulses. The results show that nonlinear refractive index coefficient is 2 × 10 -18 m2/W, two-photon absorption coefficient is 2×10-11 m/W at wavelength of 783.5 nm, and the chirp parameter of laser pulse is 1×1025 s-2. Furthermore, the mechanism of nonlinear refraction due to two-photon absorption in GaP crystal and experimental results are discussed.     

Entangling the optical frequency comb: Simultaneous generation of multiple 2 × 2 and 2 × 3 continuous-variable cluster states in a single optical parametric oscillator

We report on our research effort to generate large-scale multipartite optical-mode entanglement using as few physical resources as possible. We have previously shown that cluster-and GHZ-type N-partite continuous-variable entanglement can be obtained in an optical resonator that contains a suitably designed second-order nonlinear optical medium, pumped by at most \(\mathcal{O}\)(N ²) fields. In this paper, we show that the frequency comb of such a resonator can be entangled in an arbitrary number of independent 2 × 2 and 2 × 3 continuousvariable cluster states by a single optical parametric oscillator pumped by just a few optical modes.     

Forward acceleration and generation of femtosecond megaelectronvolt electron beams by an ultrafast intense laser pulse

We present a new mechanism of energy gain of electrons accelerated by a laser pulse.It is shown thatwhen the intensity of an ultrafast intense laser pulse decreases rapidly along the direction of propagation,electrons leaving the pulse experience an action of ponderomotivc deceleration at the descending part ofa lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain netenergy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvoltelectron beam with a bunch length shorter than 100 fs could be realized with an ultrafast(≤30 fs),intense (>10~(19)W/cm~2)laser pulse.     

Effects of Cd concentration on structure and optical properties of the ternary Zn1−xCdxO nanopowder prepared by sol–gel method

Zn_1−xCd_xO nanocrystalline powder with different Cd contents (0≤x≤1) has been prepared by new facile sol–gel route. The crystal structure and optical properties were investigated by X-ray diffraction patterns, Transmission electron microscope, X-ray photoelectron spectroscopy, Photoluminescence. As x varied from x=0 to 0.25, the Zn_1−xCd_xO nanopowder exhibits a hexagonal wurtzite structure of pure ZnO without any significant formation of a separated CdO phase. For the samples with 0.5≤x≤0.85, the Zn_1−xCd_xO nanopowder exhibits the coexistence of hexagonal ZnO and cubic CdO phase, meanwhile, the content of ZnO phase decreases while that of CdO increases with increasing the Cd content x. The ultra-violet near-band-edge emission of the Zn_1−xCd_xO nanopowder was monotonously red-shifted from 389 nm (x=0) to 406 nm (x=0.25) due to the direct modulation of band gap caused by Cd substitution.     

Effects of chromophore concentration and film thickness on thermo-optic properties of electro-optic fluorinated polyimide films

Electro-optic(EO)effect and thermo-optic(TO)effect are jointly considered on the basis of field-induced and temperature-affected perturbations of the operating point in waveguide components.TO coefficients of EO fluorinated polyimide films with side-chain azobenzene chromophore were measured by attenuated- total-reflection(ATR)technique at different temperatures with TE-and TM-polarized lights,respectively. It is found that the absolute values of TO coefficients increase with the increments of both chromophore concentration and film thickness,but the polarization dependence of TO coefficients increases with the increment of chromophore concentration and decreases with the increment of film thickness.     

Isospin Symmetry Breaking Effects on the Properties of Asymmetrical Nuclear Matter and β-Stable Matter

We have studied the influences of isospin symmetry breaking of nucleon–nucleon interaction on the various properties of asymmetrical nuclear matter and -stable matter. For asymmetrical nuclear matter, it is found that by including this isospin symmetry breaking, the changes of bulk properties increase by increasing both density and asymmetry parameter. However, these effects on the total energy and equation of state of -stable matter are ignorable. For asymmetrical nuclear matter, the validity of the empirical parabolic law in the isospin symmetry breaking case is shown. It is observed that the isospin symmetry breaking of nucleon–nucleon interaction affects the -equilibrium conditions in -stable matter.     

Determination of the thickness and optical constants of amorphous Ge–Se–Bi thin films

The effect of varying bismuth concentration on the optical constants of amorphous Ge₂₀Se_{80? x} Bi _x (where x = 0, 3, 6, 9 and 12 at%) thin films prepared by thermal evaporation has been investigated. The transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. An analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 16 (1983) p.1214], based on the use of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing bismuth content was found to affect the refractive index and extinction coefficient of the Ge₂₀Se_{80? x} Bi _x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing bismuth content, the refractive index increases while the optical band gap decreases.     

Extraction of optical constants and thickness of nanometre scale TiO2 film

TiOTiO2 薄膜 沉积物 磁电管喷射系统 X射线 发射光谱TiO₂ thin films, pointwise constrained optimization approach, constrained nonlinear programming, optical constants, parameters extractionProject supported by Shanghai Municipal Commission for Science and Technology (Grant No 03DZ14025) and National Basic Research Program of China (Grant No 2006CB300406).3/4/2005 12:00:00 AM2005-03-042005-07-28TiO2 thin films were deposited on glass substrates by sputtering in a conventional rf magnetron sputtering system. X-ray diffraction pattern and transmission spectrum were measured. The curves of refraction index and extinction coefficient distributions as well as the thickness of films calculated from transmission spectrum were obtained. The optimization problem was also solved using a method based on a constrained nonlinear programming algorithm.     

Determination of the nonlinear optical susceptibility χ(2) of surface layers by sum and difference frequency generation in reflection and transmission

The theoretical investigation of sum and difference frequency generation in thin surface layers with rotational symmetry leads to formulas which connect the generated light intensities to the surface second order nonlinear susceptibility tensor. A maximum of seven tensor components can be determined in the case of lowest symmetry. Measurements in transmission should be especially useful since they allow easy variation of both polarization and angle of incidence. On the other hand, large signal enhancements are expected for total internal reflection geometries. A consistent set of ⁽²⁾ tensor components for a thin layer of rhodamine-6G adsorbed on fused silica is found based on data from reflection and transmission measurements.     

Effects of ultrasound-assisted H2O2 on the solubilization and antioxidant activity of yeast β-glucan

Yeast β-glucan (YG) possess an extensive range of biological activities, such as the inhibition of oxidation, but the poor water solubility of macromolecular YG limits its application. In this study, through the combined degradation of ultrasonic waves and H₂O₂, and the optimization of the main process parameters for solubilizing YG by response surface methodology (RSM), a new product of YG_UH was generated. The molecular weight, structural characteristics and degradation kinetics before and after solubilization were evaluated. The results showed that the optimal solubilization conditions were reaction time: 4 h, ultrasonic power: 3 W/mL, H₂O₂ concentration: 24 %. Under these conditions, ultrasound-assisted H₂O₂ increased the solubility (from 13.60 % to 70.00 %) and reduced molecular weight (from 6.73 × 10⁶ Da to 1.22 × 10⁶ Da). Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Congo red (CR), scanning electron microscopy (SEM) revealed that ultrasound-assisted H₂O₂ increased the conformation's flexibility greatly, without changing the main structure of YG. More importantly, solubilization of YG improved free radical scavenging activity with YG_UH exhibiting the highest levels of DPPH and ABTS⁺ free radical scavenging activity. These results revealed that ultrasound-assisted H₂O₂ degradation could be a suitable way to increase the solubility of YG for producing value-added YG.     

Effects of oxygen partial pressure on optical properties of NiO_x films deposited by reactive DC-magnetron sputtering

The influence of oxygen partial pressure on the optical properties of NiOx thin films deposited by reactive DC-magnetron sputtering from a nickel metal target in a mixture gas of oxygen and argon was presented. With the oxygen ratio increasing, the reflectivity of the as-deposited films decreased, and optical band gap increased. Thermogravimetric analysis (TGA) showed that the decompose temperature of the films was above 250℃. After annealed at 400℃, only films deposited at 5% O2/Ar ratio showed high optical contrast which was about 52%. Scanning electron microscope (SEM) results revealed that the changes of surface morphology were responsible for the optical property variations of the films after annealing. Its thermal stability and high optical contrast before and after annealing made it a good potential write-once optical recording medium.