Fine 3D control of THz emission in air with dual femtosecond laser pre-pulses at tunnelling ionisation regime

• Published in: Light: advanced manufacturing Vol. 5; no. 3; pp. 1 - 13
• Main Authors: Huang, Hsin-Hui, Nagashima, Takeshi, Kumagai, Kota, Hayasaki, Yoshio, Juodkazis, Saulius, Tikhonchuk, Vladimir T., Hatanaka, Koji
• Format: Journal Article
• Language: English
• Published: Light Publishing Group 01.05.2024
• Subjects: air breakdown, spatio-temporal control; femtosecond laser induced breakdown; thz radiation
• ISSN: 2831-4093; 2689-9620; 2831-4093
• DOI: 10.37188/lam.2024.030

Emission of THz radiation from air breakdown at focused ultra-short fs-laser pulses (800 nm/35 fs) was investigated for the 3D spatio-temporal control where two pre-pulses are used before the main-pulse. The laser pulse induced air breakdown forms a ~ 120 μm-long focal volume generate shockwaves which deliver a denser air into the focal region of the main pulse for enhanced generation of THz radiation at 0.1–2.5 THz spectral window. The intensity of pre- and main-pulses was at the tunnelling ionisation intensities (1–3) × 1016 W/cm2 and corresponded to sub-critical (transparent) plasma formation in air. Polarisation analysis of THz radiation revealed that orientation of the air density gradients generated by pre-pulses and their time-position locations defined the ellipticity of the generated THz electrical field. The rotational component of electric current is the origin of THz radiation.