Effective Path Towards Relativistic Transients at Millimeter Wavelengths
  We refine the method towards extraction of sub-cycle transients in the 0.1-1 THz frequency (mm-wavelength) range from optical rectification in lithium niobate using tilted pulse fronts. Our scheme exploits previously unexplored spatio-temporal shaping of the pump pulses, resulting in highly efficient and near diffraction-limited sub-THz transients reaching 0.2 GV/m electric field strengths in free-space using only mJ-level optical ps-pulses. We address experimentally and theoretically the means to producing above-GV/m relativistic sub-THz transients with proper beam confinement and under moderate pumping conditions, thereby bringing widespread access to strong-field and nonlinear terahertz applications and devices. 
Sergio Carbajo, Anne-Laure Calendron, Huseyin Cankaya, Paula Alcorta,   Koustuban Ravi, Frederike Ahr, Xiaojun Wu, Arya Fall...
physics.optics