Spatio-temporal fine control of intense laser interaction with fluids
Hsin-hui Huang1*, Takeshi Nagashima2, Saulius Juodkazis3,4, Koji Hatanaka1,5,6
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,
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