Terahertz wave and X-ray emission enhancements under femtosecond laser double-pulse excitation on water flow

Hsin-hui Huang^1*, Takeshi Nagashima², Saulius Juodkazis^3,4, Koji Hatanaka¹

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

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

Simultaneous emission of THz wave and X-ray from thin water flow is induced by the irradiation of tightly-focused femtosecond laser pulses (35 fs, 800 nm, 0.5 kHz ) with a pre-pulse and a main pulse (Δt = 4.6ns) in air. Intensity measurements of the THz wave and X-ray were carried out with the time-domain spectroscopy (TDS) based on electro-optic sampling with a 1-mm thick ZnTe(110) crystal and a Geiger counter, respectively. Under single and double pulse excitation conditions, intensity spatial profiles of the THz wave and X-ray emission are measured as a function of the water flow position along the incident laser axis (z-axis) at the laser focus. The THz wave emission is enhanced by 100 times from the single pulse to the double pulse excitation conditions at a time delay of 4.6 ns, while only 10 times enhancement of X-ray emission is observed. The enhancement mechanisms will be discussed from the viewpoint of plasma formation and laser ablation induced by the pre-pulse irradiation.

Keywords: Terahertz, X-ray, Double pulse excitation, Ablation, Water