Generation of Terahertz Coherent Synchrotron Radiation by using Laser and Electron Beam

我们利用微密度结构的相对论电子束团成功地产生了太赫兹相干同步辐射。微结构是利用电子与激光场的相互作用产生的。在一定的共振条件下，随激光脉冲在交变磁场中运动的电子可以与激光场进行能量交换。结果，在电子聚束上产生能量调制。由于路径长度的能量依赖性，当电子聚束在加速器中前进时，这种能量调制被转换为密度调制。在分子科学研究所的UVSOR-II电子储存环上建立了这样的系统，成功地实现了亚皮秒宽的单凹陷结构的电子聚束团发射出强宽带相干太赫兹脉冲。利用飞秒激光脉冲注入储存环，形成了凹陷结构，并证明了具有亚皮秒周期微结构的电子束团发射出窄带相干太赫兹脉冲。在这种情况下，振幅调制的激光脉冲注入到环，这是由新开发的系统与法国里尔大学的研究小组合作创建的。众所周知，同步辐射是从无线电波到X射线的极宽频带。这是第一个从均匀磁场中提取单色同步辐射的实验结果。通过改变微结构的周期，可以改变辐射波长，从而实现对同步辐射的振幅和相位的控制。该方法可以在现有的同步辐射光源中实现。

We have succeeded in producing coherent synchrotron radiation in the terahertz region by using relativistic electron bunches with micro-density structures. The micro-structures were created by a newly developed method, which utilize the interaction between electrons and laser field. Electrons traveling with laser pulse in alternating magnetic field can exchange their energy with laser field under some resonant condition. As the result, an energy modulation is created on the electron bunch. This energy modulation is converted to a density modulation as the electron bunch is proceeding in the accelerator, as the result of the energy dependence of the path length. Such system has been constructed on the UVSOR-II electron storage ring in Institute for Molecular Science.We have successfully demonstrated that an electron bunch with a single dip structure of sub-picosecond width emitted intense broadband coherent THz pulse. The dip structure was created by injecting femtosecond laser pulses into the storage ring.We have also demonstrated that an electron bunch with a periodic micro-structure of a sub-picosecond period emitted narrowband coherent THz pulse. In this case, amplitude modulated laser pulses are injected into the ring, which were created by newly developed system in collaboration with a research group of Lille University France. It is well known that synchrotron radiation is extremely broadband from radio-wave to X-rays. This is the first experimental result that monochromatic synchrotron radiation is extracted from a uniform magnetic field. By changing the period of the microstructure, we could change the radiation wavelength.The results have indicated the possibility to control the amplitude and the phase of synchrotron radiation. The developed method can be realized most of the existing synchrotron light sources.