电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

Motion-induced X-ray and terahertz radiation of electrons captured in laser standing wave

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究.结果表明:垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大,逐渐从一维近周期运动演变为二维折叠运动,并产生强的微米量级波长的太赫兹辐射;高能电子垂直或者平行于激光电场方向入射到激光驻波场中,都会产生波长在几个纳米的高频辐射;低能电子与激光驻波场作用中,激光强度影响着电子的运动形式、辐射频率以及辐射强度;高能电子入射时,激光强度影响了电子高频辐射的强度,电子初始能量影响着辐射的频率;电子能量越高,产生的辐射频率越大.研究表明可以由激光加速电子的方式得到不同能量的电子束,并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源.研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.

The motions of charged particles in electromagnetic fields composed of two or more laser beams show a variety of forms due to the adjustable properties of electromagnetic fields. In this paper, we consider the periodic laser standing wave field composed of two laser beams with opposite propagating directions. The movement of electrons in the standing wave field shows a periodic behavior, accompanied with the obvious radiation, especially when electrons are captured by the laser standing wave field. This phenomenon has aroused much interest of us. Under the existing experimental conditions, the free electron beam with low energy from an electron gun or the relativistic electron beam generated from laser acceleration can be easily obtained and injected into the periodic standing wave field. In this paper, using the single- electron model and the classical radiationtheory of charged particles, we study the motion and radiation processes of low and high energy electrons in the polarized laser standing wave field. The results show that when the direction of incident electrons with low-speed is perpendicular to the direction of the laser standing wave electric field, the one-dimensional nearly periodic motion of electrons evolves into a two-dimensional folded movement by gradually increasing the light intensity of the laser standing wave field, and the strong terahertz radiation at micrometer wavelength is produced. High energy electrons generate the high-frequency radiation with the wavelength at several nanometers when the incident direction of high energy electrons is perpendicular or parallel to the direction of the laser standing wave electric field. In the case of low-energy electron, the motion of electron, frequency and intensity of radiation are affected by the laser intensity. In the case of incident high-energy electrons, the laser intensity affects the intensity of electronic radiation, and the initial electron energy influences radiation frequency. The bigger the incident electrons energy, the higher the frequency of radiation is. We can obtain electron beams with different energies by laser acceleration, and they can be promising small radiation sources for terahertz and X-ray by using the electron beam radiation in a laser standing wave field. These studies also provide a basis for experimental researches and the applications of electron radiation in a laser standing wave field.