Application of a wide-band compact FEL on THz imaging

We have developed a laboratory-scale users facility with a compact terahertz (THz) free-electron laser (FEL). The FEL operates in the wavelength range of 100-1200 μm, which corresponds to 0.3-3 THz. THz radiation from the FEL shows well-collimated Gaussian spatial distribution and narrow spectral width of Δλ/λ∼0.003, which is Fourier transform limited by the estimated pulse duration of 20 ps. The THz FEL beam shows good performance in pulse-energy stability, polarization, spectrum and spatial distribution. The main application of the FEL is in THz imaging for bio-medical researches. We are developing THz imaging techniques by two-dimensional (2D) scanning, single pulse capturing with the electro-optic method, and 3D holography. We could get the 2D imaging of various materials with the THz FEL beam. High power, coherent, and pulsed feature of the FEL radiation is expected to show much better performance in advanced THz imaging of 3D tomography. In this paper, we will show and discuss the main results of THz imaging with the different methods by using the KAERI compact FEL.