Jinguang Wang

Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence

A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60–80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions.

Characterizing, modeling, and simulating soft error susceptibility in cell-based designs in highly scaled technologies

A systematic flow is described for characterizing, modeling, and simulating single event transient-induced soft errors in cell-based designs. Pulse broadening effects are quantified for a 65 nm CMOS process.

Including Radiation Effects and Dependencies on Process-Related Variability in Advanced Foundry SPICE Models Using a New Physical Model and Parameter Extraction Approach

An automated flow is described for total-ionizing dose (TID)-aware SPICE model generation that includes TID response and its dependence on process variability and layout. A memetic algorithm that balances multiple objectives, subject to realistic constraints, is introduced for global optimization of the flow. A differential evolution algorithm is adapted for global exploration, and a modified random pattern search strategy is introduced for local exploitation. The optimizer efficiently reduces the value of different kinds of objective functions in the extraction at reasonable cost and avoids premature convergence in most practical cases. The model is implemented in Verilog-A, can be applied to all foundry model formats, and supports all popular SPICE simulators. To validate the flow, simulations from models extracted from specific targets are compared with measured current-voltage characteristics under various irradiation conditions for 0.35 μm, 0.18 μm, and 90 nm bulk CMOS processes.

Temporal evolution of femtosecond laser filament detected via magnetic field around plasma current

The temporal evolution of electron density of air plasma filament induced by femtosecond laser pulse has been studied experimentally by a single shot electromagnetic induction method. Based on the detection of transient magnetic field around the electrified filament by an induction coil, the current in filament as well as electron density is estimated from the time dependent electromotive force signal. The experimental results indicate that our method significantly reduced the self-oscillation and interference signal, which are difficult to avoid in previous standard electrical diagnostic of filament, meanwhile the reliable temporal evolution of the electron density of filament is obtained.

Ultrafast pulsed magnetic fields generated by a femtosecond laser

An ultrafast pulsed magnetic field from a two-loop solenoid is generated by a femtosecond (fs) laser. High temporal resolution is needed to measure the magnetic field. We describe an improved Faraday-rotation measurement to evaluate the evolution of the magnetic field with a resolution of ∼3.3 picoseconds (ps) in a single shot, with an uncompressed chirped pulse from a Ti:sapphire laser as the optical probe. A magnetic field of 0.52 T with a rise time of 20.8 ps has been measured with this chirped Faraday probe. In addition, we demonstrate the magnetic field strength driven by the femtosecond laser can be modified by adjusting the focal spot size.An ultrafast pulsed magnetic field from a two-loop solenoid is generated by a femtosecond (fs) laser. High temporal resolution is needed to measure the magnetic field. We describe an improved Faraday-rotation measurement to evaluate the evolution of the magnetic field with a resolution of ∼3.3 picoseconds (ps) in a single shot, with an uncompressed chirped pulse from a Ti:sapphire laser as the optical probe. A magnetic field of 0.52 T with a rise time of 20.8 ps has been measured with this chirped Faraday probe. In addition, we demonstrate the magnetic field strength driven by the femtosecond laser can be modified by adjusting the focal spot size.

Intense γ ray generated by refocusing laser pulse on wakefield accelerated electrons

Ultrafast x/γ ray emission from the combination of laser wake-field acceleration and plasma mirror has been investigated as a promising Thomson scattering source. However, the photon energy and yield of radiation are limited to the intensity of reflected laser pulses. We use the 2D particle in cell simulation to demonstrate that a 75TW driven laser pulse can be refocused on the accelerated electron bunches through a hemispherical plasma mirror with a small f number of 0.25. The energetic electrons with the maximum energy about 350 MeV collide with the reflected laser pulse of a0 = 3.82 at the focal spot, producing high order multi-photon Thomson scattering, and resulting in the scattering spectrum which extends up to 21.2 MeV. Such a high energy γ ray source could be applied to photonuclear reaction and materials science.