Intense broadband terahertz radiation via quantum coherent control

A quantum coherent control enabled, high-energy, super-broadband ultrafast tabletop high-energy tetrahertz (THz) source via two-color photoionization in gases, is demonstrated. An ultrafast pulsed laser's fundamental and second harmonic fields are mixed in a gas of atoms or molecules, causing them to ionize. A net directional electron current occurs on the timescale of the laser pulse duration and generates electromagnetic radiation at THz frequencies for sub-picosecond lasers. Results show that changing the relative phase of the laser field can effectively switch the emission between THz and harmonics. It is also found that the radiation spectrum can be readily tailored by laser energy and gas pressure control, to be applied in broadband THz spectroscopy.