China
Africa
Explore chapters and articles related to this topic
Application of Ultrafast Optoelectronics and Monolithic Distributed Microwave Photonic Devices
Published in Chi H. Lee, Microwave Photonics, 2017
Chi H. Lee, Junghwan Kim, William B. Johnson
The speed of these devices is mainly limited by the carrier lifetime of the guiding material. To measure the carrier lifetime independently, we optically pumped a tapered straight waveguide at different width sections. We increased the pumping energy so that enough carriers were injected into the waveguide and absorption was observed in a probe beam. By detecting the intensity variation of the probe beam, we could measure the recovery time of the transmitted signal and hence the carrier lifetime. In a tightly confined waveguide, diffusion to the waveguide walls dominates, where fast surface recombination occurs. In Figure 8.10a, we plot the normalized transmitted probe intensity when the waveguide was pumped at different cross sections; and in Figure 8.10b, we plot the carrier lifetime versus its diffusion length, which is approximately half the waveguide width. As can be seen, the carrier lifetime varies quadratically with the diffusion length as expected due to the diffusion processes. Since the guiding layer is made of intrinsic bulk material, ambipolar diffusion takes place where both electrons and holes contribute to the diffusion process. Using the Einstein relation, we fitted the carrier lifetime curve and extracted the ambipolar diffusion constant to be 19.2 cm2/s. The ambipolar diffusion constant calculated from published values of electrons and holes mobilities and diffusion constants of GaAs [21] is found to be 19.4 cm2/s, which is very close to the measured value. Faster response time can be obtained by DC biasing the microresonator waveguide, where a static electric field normal to the epitaxial layer is induced and rapidly sweeps the free carriers out of the waveguide core [22].
EUV-induced hydrogen plasma and particle release
Published in Radiation Effects and Defects in Solids, 2022
Mark van de Kerkhof, Andrei M. Yakunin, Vladimir Kvon, Andrey Nikipelov, Dmitry Astakhov, Pavel Krainov, Vadim Banine
During and directly after the EUV pulse, a confined plasma will fill the volume by secondary ionizations and fast expansion, and subsequently, the more mobile electrons will escape to the wall and ions will follow the electrons by ambipolar diffusion to the wall. As outlined above, initial sheath formation at the plasma-facing surfaces is frustrated by the photoelectric effect and secondary electron emission. Initially, a space-charge-limited negative sheath layer (SCL) (26), or even an inverse sheath (27), will form near the walls, confining ions. As the photoelectrons cool down to below ∼30 eV so SEY drops below unity and the UV afterglow dies out, the space-charge-limited sheath will transition to a classical plasma-wall sheath, albeit with some delay and reduced sheath potential. The delay in the formation of a classical sheath results in a dead period in ion flux after the EUV pulse; by the time the sheath is formed the photoelectrons will have cooled down to energies below 10 eV, and the effective electron temperature will be in order of ∼1 eV.
Plasma-Jet-Driven Magneto-Inertial Fusion
Published in Fusion Science and Technology, 2019
Y. C. Francis Thio, Scott C. Hsu, F. Douglas Witherspoon, Edward Cruz, Andrew Case, Samuel Langendorf, Kevin Yates, John Dunn, Jason Cassibry, Roman Samulyak, Peter Stoltz, Samuel J. Brockington, Ajoke Williams, Marco Luna, Robert Becker, Adam Cook
There are three modes in which plasmas can be accelerated in coaxial plasma guns: (1) deflagration, (2) snowplow, and (3) slab (Fig. 6). In deflagration mode, a surface flashover is caused along the insulator surface at the breech by applying a high voltage between the electrodes. An arc is formed and continues to ablate materials off the insulator surface, feeding the arc. The arc is accelerated by the j × B Lorentz force. In this mode, because the plasma is continuously added to the rear of the plasma, this is the mode for creating long plasma jets. In the snowplow mode, the gun is prefilled with a gas with the desired atomic species. An electrical breakdown is again caused at the back end of the gas column forming a current sheet by pre-ionizing a thin sheet of the gas and applying a sufficiently high voltage across the current sheet. The electrons in the current sheet carry the current and are accelerated by the Lorentz force j × B and drags the ions along by ambipolar diffusion. The neutrals ahead of the current sheet get ionized by electron impacts and become entrained in and move with the current sheet. This is the snowplow action of the current sheet, gathering up the neutrals in front of it after the neutrals become ionized.
Porous carbon architectures with different dimensionalities for lithium metal storage
Published in Science and Technology of Advanced Materials, 2022
Hamzeh Qutaish, Sang A Han, Yaser Rehman, Konstantin Konstantinov, Min-Sik Park, Jung Ho Kim
where e is the electric charge, D is the ambipolar diffusion coefficient, C is the Li+ concentration in the electrolyte, is the effective current density, is the anionic mobility, and is the Li-ion mobility.