Tunable THz radiation generation using density modulation of a relativistic electron beam

At Pohang Accelerator laboratory, at fs–THz facility, 3 THz radiation was achieved successfully using electron bunch shorter than 200 fs pulse width. To further enhance the radiation bandwidth, we use density modulation of a relativistic electron beam. In this method, a 70 MeV electron beam is first energy modulated by two optical laser-modulator and then density modulated using chicane. The density modulation at 12 THz is observed by down-converting the frequency of lasers with 800 nm and 1550 nm wavelength. The generated central frequency is found tunable for other combination of laser wavelength also. Due to proper synchronization of this THz radiation with the optical lasers; a high temporal resolution for the optical-pump THz-probe experiments can be achieved. The realization of this technique at fs–THz beamline at the PAL will enable us to make a substantial progress towards the tunable narrowband THz sources.