We present a new model of an electron gun for generating subrelativistic femtosecond （fs） electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing...We present a new model of an electron gun for generating subrelativistic femtosecond （fs） electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing electrode generates an electron energy chirp for bunching at the target. Without considering the space charge effects, simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode. Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods, the electron pulses with 1 ps can be compressed to 55 fs, which will allow significant advances in the field of ultrafast diagnosis.展开更多
The time reversal is an unique self-adaptive focusing technique important to ultrasonic imaging. In this paper, the principle and the analytic expression of the ultrasound field in the realization of time reversal du...The time reversal is an unique self-adaptive focusing technique important to ultrasonic imaging. In this paper, the principle and the analytic expression of the ultrasound field in the realization of time reversal during the presence of an interface between two media are presented. Experimental results of time reversal are given and found to agree with theoretical ones.展开更多
基金supported the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.60901036)the National Natural Science Foundation of China(Grant No.60777027)the Innovation Laboratory Fund of the Chinese Academy of Sciences(Grant No.CXJJ-10-S13)
文摘We present a new model of an electron gun for generating subrelativistic femtosecond （fs） electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing electrode generates an electron energy chirp for bunching at the target. Without considering the space charge effects, simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode. Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods, the electron pulses with 1 ps can be compressed to 55 fs, which will allow significant advances in the field of ultrafast diagnosis.
基金This project supported by National Natural Science Foundation of China and the President Foundationof Institute of Acoustics
文摘The time reversal is an unique self-adaptive focusing technique important to ultrasonic imaging. In this paper, the principle and the analytic expression of the ultrasound field in the realization of time reversal during the presence of an interface between two media are presented. Experimental results of time reversal are given and found to agree with theoretical ones.
