We generate electron beams with shorter pulse durations than the wavelength of terahertz light (300mm for 1THz light) and use these beams for the development of coherent terahertz light sources.

We compress the electron beam to a pulse duration of less than 100 femtoseconds (10^-13 seconds) using a technique called velocity bunching. The time duration of the compressed beam is only 1/100th the length of the electron beams used in the nuclear experiments at our center. To create such extremely short electron beams, we have developed a home-built thermionic cathode high-frequency electron gun. Using this electron gun, we can control the time and energy distribution of the electron beam efficiently, facilitating beam compression. Additionally, we employ a cathode with a 3mm diameter made of single crystal CeB6 (cerium hexaboride), enabling the production of low emittance electron beams.。

When the length of the electron beam becomes shorter than the wavelength of the emitted light, it is possible to obtain extremely strong coherent radiation. In the past, we have succeeded in generating high-intensity coherent undulator radiation by injecting electron beams compressed to approximately 100 femtoseconds into an undulator composed of powerful permanent magnets. In the future, we plan experiments that utilize the coherence of coherent radiation, including controlling the polarization state of terahertz light.。