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We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590 nm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being —3.66 × 10−10 m/W and —2.95 × 10−17 m2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.

A classical microcanonical 1+1-dimensional model is used to investigate the ion momentum distributions in nonsequential double ionization with linearly polarized few-cycle pulses. We find that the ion momentum distribution has a strong dependence on the carrier–envelope phase of the few-cycle pulse, which is consistent with the experimental results qualitatively. Back analysis shows that the ionization probability of the first electron at different phases and its returning kinetic energy play the main role on the ion momentum distributions.

The spatial characteristics of Thomson scattering in a linearly polarized laser field are investigated. The results show that the electron's motion and spatial distributions of Thomson scattering depend sensitively on the phase η0 at which the electron is injected to the laser field. When η0 equals to 0 or π, the electron motion is a zigzag motion and the spatial distributions of the emission show fourfold or twofold symmetry. In other cases of phases, there is a steady drift motion of electron in the transverse direction, which results in the absence of the zigzag motion and a breakdown of the symmetry of the spatial distributions as well.

Iron disilicide thin films are prepared on fused quartz using femtosecond laser deposition (FsPLD) with a FeSi2 alloy target. X-ray diffraction results indicate the films are single-phase, orthorhombic, β-FeSi2. Field scanning electron microscopy, high resolution transmission electron microscopy, UV–VIS–NIR spectroscopy and Raman microscope are used to characterize the structure, composition, and optical properties of the β-FeSi2 films. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.85 eV. The two most intense lines of Raman scattering peaked at 181.3 cm−1 and 235.6 cm−1 for the film on fused quartz, and at 191.2 cm−1 and 243.8 cm−1 for the film on Si (100), are observed.

The characteristics of backward harmonic radiation due to electron oscillations driven by a linearly polarized fs laser pulse are analysed considering a single electron model. The spectral distributions of the electron's backward harmonic radiation are investigated in detail for different parameters of the driver laser pulse. Higher order harmonic radiations are possible for a sufficiently intense driving laser pulse. We have shown that for a realistic pulsed photon beam, the spectrum of the radiation is red shifted as well as broadened because of changes in the longitudinal velocity of the electrons during the laser pulse. These effects are more pronounced at higher laser intensities giving rise to higher order harmonics that eventually leads to a continuous spectrum. Numerical simulations have further shown that by increasing the laser pulse width the broadening of the high harmonic radiations can be controlled.

Linear Thomson scattering of a short pulse laser by relativistic electron has been investigated using computer simulations. It is shown that scattering of an intense laser pulse of ~33 fs full width at half maximum, with an electron of γ0 = 10 initial energy, generates an ultrashort, pulsed radiation of 76 attoseconds with a photon wavelength of 2.5 nm in the backward direction. The scattered radiation generated by a highly relativistic electron has superior quality in terms of its pulse width and angular distribution in comparison to the one generated by lower relativistic energy electron.

In this report, we start from Lagrange equation and analyze theoretically the electron dynamics in electromagnetic field. By solving the relativistic government equations of electron, the trajectories of an electron in plane laser pulse, focused laser pulse have been given for different initial conditions. The electron trajectory is determined by its initial momentum, the amplitude, spot size and polarization of the laser pulse. The optimum initial momentum of the electron for LSS (laser synchrotron source) is obtained. Linear polarized laser is more advantaged than circular polarized laser for generating harmonic radiation.

With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected. For intensities around 10(19) W(.)mu m(2)/cm(2), an electron's energy gain near 0.1 GeV can be realized when its initial energy is 4.5 MeV, and the final velocity of the energetic electron is parallel with the propagation axis. The energy gain can be up to 1 GeV if the intensity is about 10(21) W(.)mu m(2)/cm(2). The final energy gain of the electron as a function of its initial conditions and the parameters of the laser beam has also been discussed.

By numerically solving the relativistic equations of motion of a single electron in laser fields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. When the drifting distance is comparable to or even longer than the corresponding Rayleigh length, the evolution of the beam waist cannot be neglected. The asymmetry of intensity in acceleration and deceleration leads to the conclusion that the electron can be accelerated effectively and extracted by the longitudinal ponderomotive force. For intensities above 1019 W μm2/cm2, an electron's energy gain about MeV can be realized, and the energetic electron is parallel with the propagation axis.

Theoretical studies and analytical scalings were carried out to find the optimized laser parameters and target conditions so that ultrashort hard x-ray pulses and high x-ray power could be achieved. The dependence of laser intensity and wavelength on the yield of K-shell x-ray emission was studied. We propose an optimal design for a foil target for producing high-yield hard x-ray pulses of customizing duration.

A double-cladding ytterbium-doped photonic crystal fibre (PCF) with a 350-μm2 effective area is fabricated. The measurement results show that the PCF has high absorption peak at 915 nm. Its fluorescence lifetime is 840μs. Laser experiments with all-fibre configurations are carried out with this fibre. A continuous-wave output power of 3.96 W is achieved with a 5.2 W launched pump power. The central wavelength of the output spectrum is 1080.22nm. The results show that the PCF laser has a high slope efficiency of 79.6% and light conversion efficiency of 76.2%.

When atoms and molecules are excited by ultrashort laser pulses, highly nonlinear strong-field processes like above-threshold ionization and high harmonic generation occur. By analyzing the emitted light and electron signals, the atomic and molecular structures and ultrafast dynamics can be detected with a combination of Angstrom spatial resolution and sub-femtosecond temporal resolution, which provides a powerful tool to study the basic structures and physical processes in the microscopic world. The molecular orbital tomography (MOT) developed since 2004 enables one to image the wavefunction of the molecular orbital itself, which will help people gain deeper insight into the chemical reactions. In this paper, the theory of MOT will be introduced, and the progresses of MOT in the past ten years will be reviewed.

Experiments of pulse CO2 laser produced tin plasma had been carried out. Time-integrated extreme ultraviolet spectral measurement showed that the peak of the spectrum was located at 13.5 nm. Plasma parameters of electron temperature and density measurements and the debris speed both was estimated.

A new method of x-ray holographic tomography, called pre-amplified x-ray holographic tomography, is proposed to develop an x-ray three-dimensional microscopic imaging technique. In this method, the key component is a micro zone plate taken as an imaging element like an optic lens in x-ray field. Some advantages of the method are shown by a numerical example. The method may make it possible to obtain x-ray microscopic imaging of biological specimens at high resolution in three dimensions.

Extreme ultraviolet lithography (EUVL), which uses the extreme ultraviolet radiation at a wavelength of 13.5 nm, is the leading candidate of next generation lithography addressing not only the 10 nm half-pitch nodes, but several nodes beyond that. Among all the methods for getting EUV radiation, laser-produced plasma (LPP) light source is the most promising EUV light source because of its high conversion efficiency (CE), large collect angle and low debris output. In this paper, pulsed TEA-CO2 laser and Nd:YAG laser are used to irradiate tin droplets to obtain plasma EUV emission, and the properties of EUV radiation from the plasma are studied. Results show that the EUV emission spectra induced by Nd:YAG laser have an obvious blueshift as compared with those by CO2 laser. In addition, the LPP sources are point light sources, so that the angular distribution of EUV emission from LPP can be described by Lambertian distribution.

Fluorescence resonance energy transfer (FRET) is non-radiation energy transfer that occurs between a donor (D) molecule in an excited state and an acceptor (A) molecule in a ground state by dipole-dipole interactions. The efficiency of FRET is dependent on the extent of spectral overlap between the donor photoluminescence peak and the absorption spectrum of acceptor, the quantum yield of the donor, and the distance between the donor and acceptor molecules. Currently, FRET is commonly used for determining the metal ion, analyzing the protein, biological molecular fluorescence probe, etc. In this study, the FRET between CdTe quantum dots (QDs) with different sizes and Rhodamine B (RhB) in aqueous solution is investigated by using the time-resolved fluorescence test system under two-photon excitation. In this two-photon FRET aqueous system, QD is used as donor while RhB as acceptor. The time resolved two-photon photoluminescence and fluorescence lifetime measurements are performed for analyzing the two-photon-excited luminescence by using a titanium sapphire femtosecond laser with a wavelength of 800 nm, pulse width of 130 fs, repetition frequency of 76 MHz, with the power fixed at 500 mW. The fluorescence spectrum is measured by fluorescence spectrometer and the fluorescence decay curves are recorded by single photon counter. Besides, the steady state photoluminescence is also studied with a JASCO FP-6500 Fluorescence Spectrometer. The result shows that with the increase of spectral overlap of the CdTe emission spectrum and the Rhodamine B absorption spectrum, the FRET efficiency of the QDs-RhB system becomes higher. Specifically, the fluorescence intensity of QDs decreases and the lifetime of QDs becomes shorter while RhB shows the opposite tendency. By means of the Förster theory of energy transfer, the spectral overlap integral J(λ), Foster radius R0 and the FRET efficiency E are calculated and the FRET characteristics of QD-RhB system is characterized. Theoretical analysis reveals that the physical source is the increase of the sample’s Forster radius. Moreover, the relationship between the ratio of acceptor/donor concentration and the FRET efficiency is investigated experimentally. When the ratio of acceptor/donor concentration increases, the lifetime of QDs turns shorter, and the FRET efficiency of the QDs-RhB system becomes higher. The two-photon excited FRET efficiency can reach 40.1% when the concentration of RhB is 3.0×10-5 mol·L-1. This study shows a brighter future in biological and optoelectronic applications.

Using a three-dimensional classical ensemble, we have investigated the internuclear distance (R) dependence of nonsequential double ionization (NSDI) of H2 molecules. In all alignments, as R increases, the double ionization (DI) rate first increases and then decreases, and it reaches its maxima when R is 4a.u.. The dependence of NSDI of H2 on R weakens as the angle between molecular axis and laser polarization(φ) increases. When φ is zero, the NSDI of H2 provides rich correlation patterns, which is strongly dependent on R. When φ is π/2, the correlation patterns are similar for different values of R and recollisions play a more important role in DI process. These results indicate that molecular structure has an important influence on NSDI of diatomic molecules.

The triangular Au nanoparticle array of size 37 nm was fabricated on a quartz substrate using nanosphere lithography. By performing the Z-scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearity of the Au nanoparticle array was determined. The results showed an intensity-related two-photon absorption saturation processes. As the excitation intensity increases, the nonlinear absorption changes from two-photon absorption to saturated absorption, while the nonlinear refraction exhibits self-defocusing effect. The one- and two-photon figures of merit, W=7.5 and T=0.12, were obtained, validating a high efficiency nonlinear material for all-optical switching.

A periodic triangular-shaped Au nanoparticle array is fabricated on a quartz substrate using nanosphere lithography and pulsed laser deposition, and the linear and nonlinear optical properties of metal particles are studied. The morphology of the polystyrene nanosphere mask (D = 820 nm) and the Au nanoparticle array are investigated by scanning electron microscopy. The surface plasmon resonance absorption peak is observed at 606 nm, which is in good agreement with the calculated result using the discrete dipole approximation method. By performing the Z-scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearities of Au nanoparticle array are determined. The results show that the Au particles exhibit negative nonlinear absorption and positive nonlinear refractive index with the effective third-order optical nonlinear susceptibility χ(3)eff can be up to (8.8 ± 1.0) × 10−10 esu under non-resonant femtosecond laser excitation.

The propagation of high-order harmonics with attosecond ionization gate is simulated with three-dimensional propagation equation. After 0.5 mm propagation distance， the short trajectories in the harmonics， which are generated by two 5 fs laser pulses centered at 800 and 400 nm， are selected and a highly efficient smooth supercontinuum with the bandwidth of about 80 eV is obtained in the plateau， because of the phase matching. Simulation results of different propagation distances show the broadband supercontinuum can last steadily. A highly efficient pure isolated attosecond pulse with the duration of about 135 as can be generated by directly filtering out of the harmonics from 60—90 eV in the supercontinuum， and a single 50 as pulse can be generated， which facilitates the experimental implementation for the isolated attosecond pulse generation.

Zinc oxide （ZnO） thin films have been grown on n type Si （100） substrate using femtosecond pulsed laser deposition （PLD）. The effect of change in parameters, including substrate temperature, laser energy and oxygen pressure, on the structure and optical properties of ZnO films is discussed. The Xray diffraction results show that the ZnO films are highly caxis oriented when deposited at substrate temperature of 80?℃ with laser energy of 1\^5?mJ under oxygen pressure of 10 mPa. The field emission scanning electron microscopy indicates that the mean grain size increases with the increase of temperature, but decreases with the increase of laser energy. The ultravioletvisible transmissivity shows that the annealed films have a transmittance of 90% in visible rang. The photoluminescence spectra of ZnO films are discussed. In comparison, the structure and photoluminesceme properties of ZnO films produced by using nanosecond PLD are also studied.

A new method to generate isolated broadband attosecond pulses with stable pulse duration is proposed. By adopting a few-cycle driving pulse combined with its second harmonic field, of which the polarization angle is π/3 to the driving pulse, the short path is well selected and a smooth supercontinuum with the bandwidth of about 50 eV is observed. For the intensity of the second harmonic field higher than 1014 W/cm2, the intensity variation of the second harmonic field can hardly affect the location and the bandwidth of the generated supercontinuum. Pure isolated attosecond pulses with the duration of about 100 as can be generated by directly filtering out a supercontinuum from 85—125 eV, which facilitates the experimental implement for the isolated attosecond pulse generation.

Coloured conical emission (CCE) is investigated experimentally in a β-barium borate crystal excited by intense second harmonic femtosecond pulses. Contrary sequences of green and red conical emission with variable diameters are observed at different incidence angles, which is consistent with the calculation results based on the phase matching condition. As its broad range spectrum, CCE offers an alternative means to produce an ultrafast broadband light source. It is found that the spectrum of green CE shifts toward longer wavelengths as the length of BBO crystal increased.

The nonlinear propagation of 100 fs Ti:sapphire laser pulses in a bi-refringent photonic crystal fiber is experimentally investigated. Super-continuum generation with spectra extending from 450—1050 nm was obtained and the spectra consist of distinct peaks. The spectral broadening is shown to be caused by the mechanism of spectral broadening through fission of higher-order solitons into red-shifted fundamental solitons and blue-shifted dispersion waves. The simulation of light propagation property in the waveguide can explain well the experimental results.

We report the generation of anti-Stokes emissions with wavelength 480—550nm in the secondary cores of a dual-core photonic crystal fiber from 800nm femto second laser pulses. The conversion efficiency is as high as 28%. The anti-Stokes frequency conversion of laser pulses has strong polarization dependence of the pump. The simulation of light propagation in the waveguide well explains the experimental results.

An experimental system has been set up for producing extreme ultraviolet light with high conversion efficiency by employing high power YAG laser irradiated tin slab. The dependence of extreme ultraviolet light intensity and conversion efficiency on the pump energy were studied， and the saturation effect of conversion efficiency was observed. The highest conversion efficiency of 1.6% in producing 13.5nm extreme ultraviolet light with 0.27nm bandwidth was achieved at pump energy of 250mJ, which corresponds to an intensity of 1.8×1011W/cm2.

A new method is proposed to generate extreme ultraviolet supercontinuum. The polarization gating at 1600nm is employed to intensify the ellipticity dependence of high harmonic signal， and the addition of a second harmonic field is used for modulating the ionization ratio. Calculations show that a fundamental pulse up to 6 optical cycles (32.4fs) in duration can be applied to confine the efficient high harmonic generation to half an optical cycle. This feature allows us to produce an extreme ultraviolet supercontinuum with the bandwidth of about 280eV which supports generating a Fourier-transform-limited pulse of 10as. By selecting one part of the supercontinuum， a 100as pulse is obtained directly. In addition， the intensity utilizing efficiency of fundamental pulses can be increased by making the delay between the two pulses which compose the polarization gating smaller，when the modulated polarization gating is employed.