Generation and control of strong half cycle THz radiation with ultrashort laser

Terahertz (THz) radiation provides very wide and promising applications in fields of information, non-invasive imaging, and fundamental science. The community seeks strong THz sources nowadays to access the applications from linear to non-linear range. By using an ultrashort laser illuminating a solid target, we obtain THz pulses as strong as over 100MV/cm¹ with half-cycled shape. The THz pulses are emitted in both forward and backward directions and subsequent secondary pulses are generated. The primary pulses are attributed to coherent transition radiation from hot electrons passing through the vacuum-target interfaces and secondary pulses are generated by refluxing electrons dragged back by sheath field.