Development of Variable Polarized Coherent THz Source

Terahertz (THz) radiation sources have attracted considerable interests recently, because of their potential applications in material science, medical imaging, high speed communications, etc. Vibrational circular dichroism (VCD) measurements in the THz region are extremely sensitive to conformational changes in proteins. In particular, a THz source capable of switching the left and right circularly polarization with high speed is very useful for biological analysis. One of the most efficient terahertz sources is the electron pulse of relativistic energy produced by an accelerator. A short electron pulse can produce coherent radiation at wavelength longer than electron pulse length with the intensity proportional to the square of the number of electrons contained in a pulse. Electron population in the pulse is typically the order of 107–1010 electrons, therefore high intense terahertz radiation can be produced form the short electron pulse. We have already succeeded in producing coherent undulator radiation employed the electron beam shorter than 100fs in a test-Accelerator as Coherent Terahertz Source (t-ACTS) at Tohoku University[1].Variable polarized coherent THz source, which is realized by utilizing a coherence of the undulator radiation, is under development. The polarization state of the coherent undulator radiation is manipulated using Martin-Puplett interferometer as shown in Figure 1. The linearly polarized coherent undulator radiation is split into two perpendicular waves using a wire-grid polarizer, and they are superimposed after adjusting their relative phase. The polarization control system is capable of generating arbitrary polarization states at high speed for each pulse. Demonstration of variable polarized THz source is conducted using a short undulator with 7 periods at t-ACTS. The results of this experiment will be shown in this workshop.