Transient optical non-linearity in p-Si induced by a few cycle extreme THz field

• Published in: Optics express Vol. 29; no. 4; pp. 5730 - 5740
• Main Authors: Savel'ev, Andrei, Chefonov, Oleg, Ovchinnikov, Andrei, Rubtsov, Alexey, Shkurinov, Alexander, Zhu, Yiming, Agranat, Mikhail, Fortov, Vladimir
• Format: Journal Article
• Language: English
• Published: United States 15.02.2021
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.415354

We study the impact of a few cycle extreme terahertz (THz) radiation (the field strength E ∼1-15 MV/cm is well above the DC-field breakdown threshold) on a p-doped Si wafer. Pump-probe measurements of the second harmonic of a weak infrared probe were done at different THz field strengths. The second harmonic yield has an unusual temporal behavior and does not follow the common instantaneous response, ∝ TH 2. These findings were attributed to: (i) the lattice strain by the ponderomotive force of the extreme THz pulse at the maximal THz field strength below 6 MV/cm and (ii) the modulation of the THz field-induced impact ionization rate at the optical probe frequency (due to the modulation of the free carriers' drift kinetic energy from the probe field) at the THz field strength above 6-8 MV/cm.