Abstract
Simultaneous measurements of THz wave and hard X-ray emission from thin and flat water flow when irradiated by double femtosecond laser pulses (800 nm, 35 fs/transform-limited, 0.5 kHz, delay times up to 15 ns) were carried out. THz wave measurements by time-domain spectroscopy and X-ray detection by Geiger counters were performed at the transmission and the reflection sides of the flow. THz wave emission spectra show their dynamic peak shifts toward the low frequency with the highest intensity enhancements more than 1.5 × 10 3 times in |E| 2 accumulated over the whole spectrum range of 0–3 THz at the delay time of 4.7 ns between the two pulses. On the other hand, X-ray intensity enhancements are limited to about 20 times at 0 ns under the same experimental conditions. The mechanisms for the spectral changes and the intensity enhancements in THz wave emission are discussed from the viewpoint of laser ablation on the water flow induced by the pre-pulse irradiation.
Highlights
THz science and technology [1] have been continuously growing since the early report on THz wave emission [2]
This study explores the enhancement of THz wave radiation from the simultaneous THz/X-ray emission source, which was first reported in gas, glass, and water [32,43,44]
TDS measurements of THz wave emission from a 1-mm thick -oriented ZnTe crystal set before the OAPM1 through the water flow were carried out
Summary
THz science and technology [1] have been continuously growing since the early report on THz wave emission [2]. One of the experimental methods for THz wave emission, apart from the well-developed techniques with semiconductors such as ZnTe and others [14], is through femtosecond laser-based plasma formation [15] since much higher incident laser intensity can be put into the plasma formation. While solid samples are irreversibly damaged under such intense laser irradiation conditions, air [16,17] and noble gases (He, Ne, Ar, Kr, and Xe) [18,19] have been used as targets for plasma-based THz emission, circumventing the issue. A feedback method of laser wave-front manipulation can control THz wave emission [24]. Considering the damage issue in solid samples, liquids can be an ideal target for plasma-based THz wave emission since it can be refreshed continuously during experiments
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