Generation of High-Density High-Polarization Positrons via Single-Shot Strong Laser-Foil Interaction.

We put forward a novel method for producing ultrarelativistic high-density high-polarization positrons through a single-shot interaction of a strong laser with a tilted solid foil. In our method, the driving laser ionizes the target, and the emitted electrons are accelerated and subsequently generate abundant γ photons via the nonlinear Compton scattering, dominated by the laser. These γ photons then generate polarized positrons via the nonlinear Breit-Wheeler process, dominated by a strong self-generated quasistatic magnetic field B^{S}. We find that placing the foil at an appropriate angle can result in a directional orientation of B^{S}, thereby polarizing positrons. Manipulating the laser polarization direction can control the angle between the γ photon polarization and B^{S}, significantly enhancing the positron polarization degree. Our spin-resolved quantum electrodynamics particle-in-cell simulations demonstrate that employing a laser with a peak intensity of about 10^{23} W/cm^{2} can obtain dense (≳10^{18} cm^{-3}) polarized positrons with an average polarization degree of about 70% and a yield of above 0.1 nC per shot. Moreover, our method is feasible using currently available or upcoming laser facilities and robust with respect to the laser and target parameters. Such high-density high-polarization positrons hold great significance in laboratory astrophysics, high-energy physics, and new physics beyond the standard model.

[Research on enhancement of the extraction efficiency of C-band LED with 2D photonic crystals].

On-chip light source is the main development part of the optoelectronic systems in the future. As on-chip light source, the main disadvantage of LED is its low extraction efficiency. Photonic crystal is an efficient method to increase the extraction efficiency of LED. The structure and parameters of the C-band LED was designed and the band gap of the 2D photonic crystals for different arrangement and different ratio was calculated using the finite-difference time-domain (FDTD) method, and then the best structural parameters of the 2D photonic crystals were determined using the method of band gap theory in this paper. Results show that the best structure is air holes PC with a triangular arrangement having a lattice constant of 500 nm and a ratio of 0.44.

[Research on demodulation system for human body temperature measurement of intelligent clothing based on arrayed waveguide grating].

A system for demodulating distributed fiber Bragg grating sensors of the intelligent clothing was researched and realized, which is based on arrayed waveguide grating. The principle of demodulation method based on arrayed waveguide grating was analyzed, intensity--demodulating method was used to interrogate the wavelength of the fiber Bragg grating based on the building up of an experimental platform, and demodulation experiment of pre and post series of fiber Bragg grating was completed. The results show that the wavelength demodulation of the system has high linearity for fiber Bragg grating, the system gives a wavelength accuracy of 0.001 nm, and demodulation error caused by crosstalk between different sensors is 0.0005 nm. The measurement error of human body temperature is +/- 0.16 degrees C. It can be applied to the human body temperature measurement.