Generation and Detection of THz Pulses With a Bandwidth Extending Beyond 4 THz Using a Subpicosecond Yb-Doped Fiber Laser System

We experimentally demonstrate the generation and detection of broadband THz pulses with a bandwidth extending beyond 4 THz by using a 1.04- μm Yb-doped fiber laser with a pulse duration of 0.48 ps. Owing to higher order nonlinear processes (such as the cascaded χ⁽²⁾ process and χ⁽³⁾ process) in LiNbO₃ crystals, THz pulses can be emitted efficiently with a bandwidth extending beyond the boundaries of the spectral width of the excitation pulse. By compressing divided sampling pulses to as short as 80 fs, we detected the THz pulse in the full spectral range, which could not be resolved with the original pulse. The precise control of the nonlinear effects and the compression of the sampling pulses compensated for the disadvantage of using a 1- μm fiber laser. This work will contribute to the progress of nonlinear THz spectroscopy.