Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

S Mondal,S Sun,M A Fareed,H A Hafez,W J Ding,J Zhang,T Ozaki,X Ropagnol,Z M Sheng,G Zhang,Q Wei,A Laramée

doi:10.1038/srep40058

Abstract

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

Highlights

(b) Comparison of THz pulse energy generated from nanorod (NR) targets of different nanorod lengths (h) and diameter (D) of 200 nm in the spectral range ≤20 THz; (c) THz pulse energy generated from nanorod targets with different nanorod (NR) lengths, with high-pass window in spectral range from 20 THz to 200 THz
We have demonstrated that the THz pulse energy can be increased by using aligned Cu nanorod array targets, with a maximum enhancement of up to 13.8 times for ≤20 THz and 28 times in the spectral range between 20 THz and 200 THz
PIC simulations reveal the mechanism behind the intense THz pulse generation by this technique, which we attribute to coherent transition radiation at THz frequencies by the energetic electrons produced by the laser plasma interactions

Summary

Introduction

(b) Comparison of THz pulse energy generated from nanorod (NR) targets of different nanorod lengths (h) and diameter (D) of 200 nm in the spectral range ≤20 THz; (c) THz pulse energy generated from nanorod targets with different nanorod (NR) lengths, with high-pass window in spectral range from 20 THz to 200 THz. We first study transition radiation in the THz frequency range generated by relativistic intensity laser-plasma interaction using thick copper (Cu) targets.

Results

Conclusion