Spatio-temporal fine control of intense laser interaction with fluids

Hsin-hui Huang^1*, Takeshi Nagashima², Saulius Juodkazis^3,4, Koji Hatanaka^1,5,6

¹Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
²Faculty of Science and Engineering, Setsunan University, Osaka, Japan
³Center for Micro-Photonics, Swinburne University of Technology, Melbourne, Australia
⁴Melbourne Centre for Nanofabrication, the Victorian Node of the Australian National Fabrication Facility, Clayton, Australia
⁵College of Engineering, Chang Gung University, Taoyuan, Taiwan
⁶Department of Materials Science and Engineering, National Dong-Hwa University, Hualien, Taiwan

* Presenter:Hsin-hui Huang, email:hsinhuih@gate.sinica.edu.tw

THz wave emission from air or a flat water-flow (15μm-thick) is studied with time-domain spectroscopy under the double pulse irradiation of tightly-focused femtosecond laser (35fs, 800nm, 0.5kHz) with spatio-temporal offsets; Δx, Δy up to 50μm and Δt up to 15ns. Under such double pulse irradiation conditions, THz emission is enhanced 13-times for air and 1,500-times for the water-flow, respectively. THz polarization which reflects electron trajectories, under ablation/plasma conditions, shows linear polarization aligned to the air-shockwave expansion in air and circular-polarization with the water-flow. It is clearly shown that the alignment of the linear polarization in air and the handedness of the circular polarization with the water-flow can be finely controlled by the spatio-temporal offsets. Mechanisms related are discussed from the viewpoints of the air-shockwave dynamics with its asymmetric density profile and the water ablation dynamics for the main pulse interaction in front of the water-flow.

Keywords: THz, air, water, double pulse excitation, intense laser