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Updated: Jun 27, 2025

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies
Published on: December 18, 2015
Millijoule Terahertz Radiation from Laser Wakefields in Nonuniform Plasmas
Linzheng Wang1,2, Zhelin Zhang1,2,3, Siyu Chen1,2
1Key Laboratory for Laser and Plasma (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
Abstract:
We report the experimental measurement of millijoule terahertz (THz) radiation emitted in the backward direction from laser wakefields driven by a femtosecond laser pulse of few joules interacting with a gas target. By utilizing frequency-resolved energy measurement, it is found that the THz spectrum exhibits two peaks located at about 4.5 and 9.0 THz, respectively. In particular, the high frequency component emerges when the drive laser energy exceeds 1.26 J, at which electron acceleration in the forward direction is detected simultaneously. Theoretical analysis and particle-in-cell simulations indicate that the THz radiation is generated via mode conversion from the laser wakefields excited in plasma with an up-ramp profile, where radiations both at the local electron plasma frequency and its harmonics are produced. Such intense THz sources may find many applications in ultrafast science, e.g., manipulating the transient states of matter.
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