High-power THz to IR emission by femtosecond laser irradiation of random 2D metallic nanostructures.

Liangliang Zhang,Hai Wang,X.-C Zhang,Yunsong Zhou,Kaijun Mu,Cunlin Zhang

doi:10.1038/srep12536

Liangliang Zhang, Hai Wang + Show 4 more

Open Access

https://doi.org/10.1038/srep12536

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Abstract

Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research, and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

Highlights

After irradiating a surface with a femtosecond laser pulse, a fraction of the absorbed laser energy is retained in the surface layer of the sample and dissipates into the bulk sample via heat conduction as residual thermal energy[31,32]
It has been determined that a significant amount of residual energy can be deposited in samples through surface roughness effects, exothermic chemical processes and ambient gas pressure effects[33]
According to the Stefan-Boltzmann law, the thermal radiation power is proportional to the temperature to the fourth power

Summary

Introduction

We used a randomly roughened surface to realize momentum matching over a wide range of wave vectors[28,29]. It has been determined that a significant amount of residual energy can be deposited in samples through surface roughness effects, exothermic chemical processes and ambient gas pressure effects[33]. We identified strong THz to IR thermal radiation from a randomly roughened metallic surface. We optimized the design of the metal deposition parameters to realize mW-level radiation intensity and an ultra-broadband (~150 THz) frequency spectrum. An intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. The coherent THz signal was enhanced with the pump fluence because the laser absorptivity was enhanced by the thermal effect of the metal surface

Methods

Results

Conclusion