Intensification of the electric field of high repetition terahertz excitation pulses for time-resolved STM

Abstract

Due to the recent technological innovation of intense terahertz (THz) pulses, ultrafast control of crystal and molecular structures using THz electric fields has been extensively studied. In this case, the THz pulse must have a large electric field as large as the Coulomb field between lattice points. In order to image such ultrafast dynamics in real space using time-resolved STM, THz pulses, which play the role of excitation light, are required to have a high repetition of MHz or higher. Using a pulsed laser with a center wavelength of 1030 nm, a pulse duration of 300 fs, and an average power of less than 20 W, and a high repetition rate of 4 MHz, we have developed a strong electric field for THz pulses generated by the optical rectification effect of a nonlinear optical crystal BNA.