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Electrical characteristics of In0.05Ga0.95N/Al0.07Ga0.93N and In0.05Ga0.95N/GaN multiple quantum well (MQW) ultraviolet light-emitting diodes (UV-LEDs) at 400 nm wavelength are measured. It is found that for InGaN/AlGaN MQW LEDs, both ideality factor and parallel resistance are similar to those of InGaN/GaN MQW LEDs, while series resistance is two times larger. It is suggested that the Al0.07Ga0.93N barrier layer did not change crystal quality and electrical characteristic of p-n junction either, but brought larger series resistance. As a result, InGaN/AlGaN MQW LEDs suffer more serious thermal dissipation problem although they show higher light output efficiency.

We present the evolutions of the electron temperature and plasma expansion velocity with Thomson scattering experiment. The observed time-resolved ion-acoustic image is reproduced by a numerical code which couples the Thomson scattering theory with the output parameters of the one-dimensional hydrocode MEDUSA.

Long plasma channels induced by femtosecond laser pulses in air are diagnosed using the sonographic method. By detecting the sound signals along the channels, the length and the electron density of the channels are measured. Refocusing is also observed at different laser energies and different focal lengths. We find that the sonographic method has manifest advantages compared to other techniques.

Spatial distribution of hot electrons with energies above 50 keV are investigated by an ethanol micro-droplet spray irradiated by linearly and elliptically polarized 150 fs laser pulses at an intensity of 1016W/cm2. Two symmetric hot electron jets with respect to the laser propagation direction are observed in the polarization plane for a linearly polarized laser field and in the plane of the long electric vector for an elliptically polarized laser field, respectively. Particle-in-cell simulations suggest that the resonance absorption on the spherical surface of the droplets is mainly responsible for the generation of the double-jet emission of hot electrons.

InGaN/GaN MQWs, InGaN/AlGaN MQWs and InGaN/AlInGaN MQWs are grown on (0001) sapphire substrates by MOCVD. Membrane samples are fabricated by laser lift-off technology. The photoluminescence spectra of membranes show a blue shift of peak positions in InGaN/GaN MQWs, a red shift of peak positions in InGaN/AlGaN MQWs and no shift of peak positions in InGaN/AlInGaN MQWs from those of samples with substrates. Different changes in Raman scattering spectra and HR-XRD (0002) profile of InGaN/AlInGaN MQWs, from those of InGaN/GaN MQWs and InGaN/AlGaN MQWs, are observed. The fact that the strain changes differently among InGaN MQWs with different barriers is confirmed. The AlInGaN barrier could adjust the residual stress for the least strain-induced electric field in InGaN/AlInGaN quantum wells.

High coupling efficiency generation in water confined laser plasma propulsion is investigated. It is found that the coupling efficiency is enhanced over thirty times in water confined ablation compared to that of direct ablation. From calculation of the ablation pressure induced by the plasma on the target surface, it is realized that high coupling efficiency is attributed to the confinement of the water layer on the plasma expansion.

Strong white light emission is observed from femtosecond laser propagation in air. The divergence angle of the white light emission is measured to be about 5 mrad. Young's double-slits and a Michelson interferometer are used to investigate the coherence. The wavelength components of the white light emission are identified to have a good spatial coherence and a coherence time of about 0.5 ps.

An x-ray laser shadowgraphy experiment was conducted on Xingguang-II laser facility in 1996. A multi-layer spherical mirror was used as an imaging element and a high sensitivity CCD camera as a detector. We measured the near-field image of the Ti x-ray laser beam. With a Ti x-ray laser beam as a backlight source, we obtained a clear Cu mesh image, demonstrating the potential as advanced diagnostic measurements to study high density plasmas in inertial confinement fusion research.

The Mg-delta-doped GaN structure has been grown by low-pressure metalorganic chemical vapour deposition. The Hall-effect measurements reveal that the electrical properties are enhanced. The hole concentration is enhanced twice and hole mobility is enhanced three times by Mg-delta doping. Both the etch pit density data and the x-ray diffraction data demonstrate that Mg-delta doping can reduce the threading dislocation density of p-type GaN epilayer.

An InGaN multiple-quantum-well (MQW) violet-light-emitting diode (LED) is grown by low-pressure metalorganic chemical vapour deposition. It is found that photoluminescence wavelength of the InGaN MQW violet LED is lengthened with increasing growth temperature and with the increasing trimethylindium flow of the InGaN wells. The electroluminescence peak wavelength of the violet LED are about 401 nm with full width at half maximum of 14 nm, and the output power in injection current of 20 mA at room temperature is 4.1 mW.

We investigated the characteristics of argon and helium gas jets produced by a cylindrical nozzle under pressures from 1 to 6 MPa using a femtosecond laser interferometry. A radial parabolic distribution and an axial exponential distribution of the gas jet density profiles are identified. The results show that the density increases linearly with the backing pressure.

The near-ultraviolet lighting-emitting-diodes (UV-LEDs) with the InGaN/GaN multi-quantum-well (MQW) structure were grown by low-pressure metalorganic vapour phase epitaxy. The double crystal x-ray diffraction revealed a distinct second-order satellite peak. The near-ultraviolet InGaN/GaN MQW LEDs have been successfully fabricated to emit at 401.2 nm with narrow FWHM of 14.3 nm and the forward voltage of 3.6 V at 20 mA injection current at room temperature. With increasing forward current from 10 mA to 50 mA, the redshift of the peak wavelength was observed due to the band-gap narrowing caused by heat generation.

The effects of laser polarization on super-hot electron (> 100 keV) generation have been studied in the interaction of femtosecond laser light (800 nm, 150 fs, 6 x 10(15) W(.)cm(-2)) with a pre-formed plasma from a slab Cu target. For p-polarized laser pulses, high-energy gamma -rays of the energy similar to 400keV were detected. The electron temperatures deduced from the gamma -ray spectra were 66 and 52 ke V, respectively, in normal and reflective directions of the solid target, and hot electrons were emitted out of the plasma mainly in the normal direction. In contrast, there were nearly no gamma -rays > 100keV found for s-polarized laser pulses. The hot electron temperature was 26 keV and the emission of hot electrons was parallel to the laser field. The superposition of resonant field with electrostatic field excited by escaping electrons may contribute to the high-energy gamma -ray or super-hot electron (> 100keV) generation.

We demonstrate a 100-TW-class femtosecond Tr:sapphire laser running at a repetition rate of 0.1 Hz based on a 20 TW/10 Hz laser facility (XL-II). Pumping the new stage amplifier with a 25J green Nd:glass laser, we successfully improve the laser energy to 3.4 J with duration of 29 fs, corresponding to a peak power of 117 TW.

A real-time ion spectrometer mainly based on a high-resolution Thomson parabola and a plastic scintillator is designed and developed. The spectrometer is calibrated by protons from an electrostatic accelerator. The feasibility and reliability of the diagnostics are demonstrated in laser-driven ion acceleration experiments performed on the XL-II laser facility. The proton spectrum extrapolated from the scintillator data is in excellent agreement with the CR39 spectrum in terms of beam temperature and the cutoff energy. This real-time spectrometer allows an online measurement of the ion spectra in single shot, which enables efficient and statistical studies and applications in high-repetition-rate laser acceleration experiments.

The emission lines of B, C, O and Fe in tokamak plasma are reported. The spectra are compared with those calculated by the CHIANTI code, which is based on the collisional-radiative models with a large amount of accurate atomic data. General agreement is obtained between the results of experiment and computation. Most of the lines in the spectra are identified, and the relative number density ratios of B, C, O and Fe are determined. It is found that the processes of line formation in our experiment are similar to those in the stellar coronae. The line-averaged electron density of the tokamak plasma is measured by the HCN laser, indicating a good agreement with the theoretical prediction by the density-dependent line ratio of Fe XXI.

GaN-based thin film vertical structure light-emitting diodes (VS-LEDs) were fabricated by a modified YAG laser lift-off (LLO) process and transferred to Cu substrates. With a comparison of the electrical and optical properties of conventional LEDs on sapphire substrates and of lateral structure thin film LEDs by a KrF LLO process, the vertical structure of LLO LEDs shows obvious superiority. LLO VSLEDs made by modified YAG LLO process show less increase of leakage current than the devices made by conventional KrF LLO process. Furthermore, owing to the well current spreading and less current path, the ideality factors and series resistance of vertical structure LEDs reduce greatly and the efficiency increases more obviously than the lateral structure LEDs, which is also reflected on the relative L-I curves. The output power of vertical structure LEDs is over 3 times greater than that of the lateral structure LLO LEDs within 300mA.

We utilize an interferometer to investigate the changes of the refractive index caused by dielectric barrier discharge plasma. The electronic density of the plasma produced is measured and analyzed tentatively. The results show that density of the plasma increases linearly with exciting voltages.

Polarization-resolved edge-emitting electroluminescence (EL) studies of InGaN/GaN MQWs of wavelengths from near-UV (390 nm) to blue (468 nm) light-emitting diodes (LEDs) are performed. Although the TE mode is dominant in all the samples of InGaN/GaN MQW LEDs, an obvious difference of light polarization properties is found in the InGaN/GaN MQW LEDs with different wavelengths. The polarization degree decreases from 52.4% to 26.9% when light wavelength increases. Analyses of band structures of InGaN/GaN quantum wells and luminescence properties of quantum dots imply that quantum-dot-like behavior is the dominant reason for the low luminescence polarization degree of blue LEDs, and the high luminescence polarization degree of UV LEDs mainly comes from QW confinement and the strain effect. Therefore, indium induced carrier confinement (quantum-dot-like behavior) might play a major role in the polarization degree change of InGaN/GaN MQW LEDs from near violet to blue.

Ultra-violet (KrF excimer laser, λ = 248 nm) laser lift-of (LLO) techniques have been operated to the GaN/sapphire structure to separate GaN from the sapphire substrate. Hexagonal to cubic phase transformation induced by the ultra-violet laser lift-of (UV-LLO) has been characterized by micro-Raman spectroscopy, micro-photoluminescence, along with high-resolution transmission electron microscopy (HRTEM). HRTEM indicates that UV-LLO induced phase transition takes place above the LLO interface, without phase transition under the LLO interface. The formed cubic GaN often exists as nanocrystal grains attaching on the bulk hexagonal GaN. The half-loop-cluster-like UV-LLO interface indicates that the LLO-induced shock waves has generated and played an assistant role in the decomposition of the hexagonal GaN and in the formation of cubic GaN grains at the LLO surface.