Terahertz (THz) radiation finds important applications in various fields, making the study of THz sources significant. Among different approaches, electron accelerator-based THz sources hold notable advantages in generating THz radiation with narrow bandwidth, high brightness, high peak power, and high repetition rate. To further improve the THz radiation energy, the bunching factor of the free electron bunch train needs to be increased. We propose and numerically reveal that, by adding an additional short-pulse drive beam before the main beam as the excitation source of nonlinear plasma wake, the bunching factor of the main beam can be further increased to ∼0.94, even though with a relatively low charge, low current, and relatively diffused electron beam. Two such electron beams with loose requirements can be easily generated using typical photoinjectors. Our work provides a way for a new THz source with enhanced radiation energy.
Optical cavity always acts as a valuable tool for basic research and diagnostics. By using a steady-state microbunching (SSMB) technique, a cavity for a new light source is created. We present a continuous-wave optical cavity relying on a steady-state microbunching (SSMB) mechanism for a new light source. A beam evolution model is established to calculate the final beam size under different power with the help of ABCD matrics and Winkler model. A planar four-mirror cavity has been developed using a continuous-wave laser injection system with minimum phase noise. The modal instability effect is found as a result of the surface thermoelastic deformation of cavity mirrors. To eliminate the high-order modes, a pair of D-shaped mirrors are used and 30 kW intra-cavity power is obtained.
The coherent beam combination of kW fiber lasers with a filling aperture has been in research. An experiment is set up to achieve the coherent beam combination. The coherent beam combination of two fiber lasers with a filling aperture is realized, and the phase bandwidth of the beam combination is measured and analyzed. The laser spots before and after the combination are detected respectively. The phase noise of high power laser is measured and the factors affecting the phase noise are analyzed.
A Thomson scattering X-ray source can produce quasi-monochromatic and continuously energy-tunable X-rays characterized by small focal spot and high brightness, which makes it an excellent light source for K-edge imaging. In this paper, the experimental feasibility of K-edge imaging was demonstrated at the Tsinghua Thomson scattering X-ray source (TTX). The phantom was a plastic test tube filled with sodium iodide (NaI)- loaded water solutions with I concentrations ranging from 5 to 300 mg/ml. Well agreement between the measured equivalent projection integral of the linear attenuation coefficient of the phantom and the theoretically predicted value was witnessed. The influence of X-ray bandwidth on the image quality was discussed. Based on the continuous tunability of scattered X-ray energy, the K-edge subtraction imaging was tested and obvious contrast enhancement was achieved. Our results pave the way towards practical application of K-edge imaging at the TTX.
Based on the collision of intense laser and relativistic electrons, a Thomson scattering x-ray source can produce quasi-monochromatic x-ray pulses with high brightness in the tens keV or even higher energy regime, which can eliminate the beam hardening effect encountered in computed tomography (CT) by using polychromatic x-rays generated through Bremsstrahlung and make it possible to relate the reconstructed linear attenuation coefficients to the composition of a material. In this paper, we demonstrate the capacity of quantitative CT measurement based on Tsinghua Thomson scattering X-ray source (TTX) and the potential of anatomical segmentation using quantitative linear attenuation coefficient analysis. A peanut sample (Arachis hypogaea L.) was chosen for this study. According to the reconstructed CT image, all anatomical structures except for the testa (i.e. the seed coat) of peanut were identified clearly in terms of the shape and size, and there were high similarities between reconstructed linear attenuation coefficients of cotyledon and its theoretical values. After quantitative analysis of the reconstructed linear attenuation coefficients, the hull can be peeled off the core at the threshold of 0.31 cm-1. Our results pave the way towards fundamental researches and practical applications based on quantitative CT at TTX.
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