A major frontier in strong field laser physics and nonlinear optics is the interaction of powerful terahertz (THz) pulses with matter. A plethora of scientific challenges and applications are presently under study, like table-top electron acceleration, THz-enhanced attosecond pulse generation and strong electric and magnetic THz field interactions with matter. However, despite the rapid development of THz science during the last two decades, the majority of available table-top THz sources remain rather weak limiting the interactions of THz radiation with matter mostly in the realm of linear optics. In this work, using intense ultrashort mid-infrared laser pulses to drive laser beam filamentation in ambient air, we demonstrate generation of sub-millijoule single-cycle THz pulses with unprecedented THz conversion efficiency (>2%), exceeding by far any previously reported experimental values for plasma-based THz sources. Moreover, due to the large bandwidth of the generated THz radiation (∼20 THz), the peak THz electric and magnetic fields exceed the 100 MV/cm and 33 tesla, respectively. Based on the reported experimental findings and theoretical estimates, it is projected that soon multi-millijoule THz pulses with peak electric and magnetic fields in the gigavolt per centimeter and kilotesla level, respectively, will become available. Quasi-static ultrashort electric and magnetic bursts at these intensities will enable extreme nonlinear and relativistic science.

More information can be found in: A. D. Koulouklidis, C. Gollner, V. Shumakova, V. Y. Fedorov, A. Pugžlys, A. Baltuška, and S. Tzortzakis,
“Observation of extremely efficient terahertz generation from mid-infrared two-color laser filaments.”
Nature Communications,
11, 292 (2020).