Dong Zhiwei

Off-Resonant Third-Order Optical Nonlinearity of an Ag:TiO2 Composite Film

Using the femtosecond time-resolved optical Kerr effect technique, we investigate the off-resonant nonlinear optical response of an Ag:TiO2 composite film prepared by a vacuum magnetron sputtering method. The third-order nonlinear optical susceptibility of the composite film with silver nanoparticle size of about 30 nm is estimated to be 1.9×10−10 esu at the incident laser wavelength of 800 nm. When the photon energy of the incident beam is lower than that for surface plasmon or the interband transition of silver nanoparticles, the observed third-order optical nonlinearity is attributed to the intraband transition of the free electrons. Based on the linear limit of the electric field within micro-spherical model, we assign this large optical nonlinearity to the local field enhancement of the third-order nonlinearity.

Fast Theoretical Simulation for Design of Helical Flux Compression Generators

A theoretical scheme is derived to achieve the numerical simulation of helical flux compression generator (HFCG) design, by which not only any physical approximation is not made, but also numerical simulation can be fast obtained. In particular, an analytic formula to calculate the inductance is deduced, which is extremely close to the experimental results. The physical process of relevant interesting physical quantity, such as inductance, enlarging current, and magnetic flux density, can be calculated to compare with the experimentally quantitative results.

Femtosecond Third-Order Optical Nonlinearity of Au:Bi2O3 Nanocomposite Films

Ultrafast third-order optical nonlinearities of the as-deposited and annealed Au:Bi2O3 nanocomposite films deposited by magnetron cosputtering are investigated by using femtosecond time-resolved optical Kerr effect (OKE) and pump–probe techniques. The third-order optical nonlinear susceptibility is estimated to be 2.6×10−10 esu and 1.8×10−9 esu at wavelength of 800 nm, for the as-deposited and the annealed film, respectively. The OKE signal of the as-deposited film is nearly temporally symmetrical with a peak centred at zero delay time, which indicates the dominant contribution from intraband transition of conduction electrons. For the annealed film, the existence of a decay process in OKE signal implies the important contribution of hot electrons. These characteristics are in agreement with the hot electron dynamics observed in pump–probe measurement.

Numerical study on high power microwave flashover and breakdown on output-window by EM-fluid simulation

Summary form only given. An electromagnetic-field FDTD method coupled with plasma fluid model is put forward to study the phenomena of High Power Microwave flashover and breakdown on output-window. The numerical results could be concluded as follows. For flashover and breakdown on outer surface, output microwave pulse is shortened without cut-off; there is a standing-wave distribution of electric field RMS (Root-Mean-Square) value before the window with fixed-positions of wave nodes and antinodes; there is a ultra-high-density (~1021/m3) and ultra-thin (~mm) plasma shell with slow diffusion, microwave could penetrate the plasma-shell partly; the shortening of output microwave is caused by plasma absorption mostly. The output pulse of microwave could be lengthened by decrease the initial density or depth of plasmas; the other way is to shorten incident microwave pulse or decrease the value of incident microwave power. For flashover and breakdown on inner surface, there is also a standing-wave distribution of electric field RMS value before the window but the positions of wave nodes and antinodes varying with time; the plasma region move to the direction of microwave source; with strong-outgassing, output microwave pulse is shortened without cut-off, there are a “thread-like” ultra-high-density (~1021/m3) and ultra-thin (~mm) plasma regions with slow diffusion, the distance between two “thread-like” region is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and low electric field value, the output pulse of microwave are lengthened but cut-off finally, there are a “belt-like” high-density (~1018/m3) and thin (mm~cm) plasma regions with fast diffusion, the distance between two “belt-like” region is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and high electric field value, output pulse of microwave is cut-off quickly, a “block-like” diffuse ultra-high-density (~1021/m3) and deep (~cm) plasma regions are formed with very fast diffusion, the shortening of output microwave is caused by plasma reflection mostly.

Irradiation Effects of Femtosecond Pulses on Refractive Index of Ag-Embedded Nanocomposite Glasses

The irradiation effects of femtosecond pulses on Ag-embedded composite glasses fabricated by ion-exchange are investigated using z-scan measurement. Both changes of the refractive index caused by the laser irradiation effect and the third-order optical nonlinearity are observed in the experiment. Taking the change of the linear and nonlinear refractive index into consideration, the fitting results are in agreement with the experimental results.

A Simple Model for Ignition of Magnetized Target Fusion

A simple model for magnetized target fusion is proposed. Self-consistent equations are made as equivalent circuit is included. Ignition conditions and physical process are analyzed with practical parameters. It is shown that system temperature rises as external work is equal to or greater than the loss of Bremsstrahlung, and ignition of target happens as thermonuclear reaction energy is equal to or greater than the radiation loss from the target.

Two-Photon Absorption and Excited State Dynamics of Two Organic Molecules Containing Donor/Acceptor Moieties

Two new two-photon absorption (TPA) molecules, named SK-G1 and NT-G1, are synthesized and the photo-physical characteristics are investigated by using linear absorption spectra, one-photon fluorescence spectra and two-photon excited fluorescence spectra. Both the compounds exhibit TPA properties, and the TPA values determined by z-scan measurement are 10GMand 39GMfor SK-G1 and NT-G1, respectively, at wavelength 800nm. Time-resolved spectroscopic techniques are employed to further explore the excited state dynamics of NT-G1with larger TPA cross section. The research results show that there is an ultrafast intraband energy transfer process (about 3ps) before the formation of charge transfer state with a relatively long lifetime.

Effect of Photo-Oxidation on Energy Transfer in Light Harvesting Complex (LH2) from Rhodobacter Sphaeroides 601

We study the photo-oxidation of bacteriochlorophylls (BChls) in peripheral light harvesting complexes (LH2) from rhodobacter sphaeroides by using the steady absorption and the femtosecond pump–probe measurement, to realize the detailed dynamics of LH2 in the presence of photo-oxidation. The experimental results reveal that BChl-B850 radical cations may act as an additional channel to compete with the unoxidized BChl-B850 molecules for rapidly releasing the excitation energy, while the B800→B850 energy transfer rate is almost unaffected in the oxidation process.