Generation of broadband terahertz Laguerre-Gaussian beam

In this study, a method to generate a broadband THz Laguerre-Gaussian (LG) beam is demonstrated. The generation of broadband THz radial beam by using segmented nonlinear optical crystals with threefold rotational symmetry was recently reported. This radial beam can be converted to LG beam by using a quarter wave plate and a polarizer. A Ti:sapphire regenerative amplifier with wavelength of 800 nm, pulse duration of 100 fs, and pulse energy of 0.8 mJ is used as a fundamental light sourse. The fundamental beam is converted to the mode with a predesigned polarization distribution by using segmented half wave plates, and generates the THz radial beam with optical rectification in a GaP(111) crystal. As a THz quarter wave plate and polarizer, total reflection in high-resistivity silicon prism and wire grid polarizer are employed, respectively. At the focal point of THz LG beam, THz electric field is detected by electro-optic sampling with a ZnTe(110). The probe beam is scanned two-dimensionally in order to obtain the field distribution.