Broadband terahertz wave generation from an epsilon-near-zero material

Wenhe Jia; Meng Liu; Yongchang Lu; Xi Feng; Qingwei Wang; Xueqian Zhang; Yibo Ni; Futai Hu; Mali Gong; Xinlong Xu; Yuanyuan Huang; Weili Zhang; Yuanmu Yang; Jiaguang Han

doi:10.1038/s41377-020-00452-y

Broadband terahertz wave generation from an epsilon-near-zero material

Light Sci Appl. 2021 Jan 7;10(1):11. doi: 10.1038/s41377-020-00452-y.

Authors

Wenhe Jia¹, Meng Liu², Yongchang Lu², Xi Feng², Qingwei Wang², Xueqian Zhang², Yibo Ni¹, Futai Hu¹, Mali Gong¹, Xinlong Xu³, Yuanyuan Huang³, Weili Zhang⁴, Yuanmu Yang⁵, Jiaguang Han⁶

Affiliations

¹ State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing, 100084, China.
² Center for THz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin, 300072, China.
³ Shaanxi Joint Lab of Graphene, International Collaborative Center on Photoelectric Technology and Nano Functional Materials, Institute of Photonics and Photon-Technology, Northwest University, Xi'an, 710069, China.
⁴ School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma, 74078, USA.
⁵ State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing, 100084, China. ymyang@tsinghua.edu.cn.
⁶ Center for THz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin, 300072, China. jiaghan@tju.edu.cn.

Abstract

Broadband light sources emitting in the terahertz spectral range are highly desired for applications such as noninvasive imaging and spectroscopy. Conventionally, THz pulses are generated by optical rectification in bulk nonlinear crystals with millimetre thickness, with the bandwidth limited by the phase-matching condition. Here we demonstrate broadband THz emission via surface optical rectification from a simple, commercially available 19 nm-thick indium tin oxide (ITO) thin film. We show an enhancement of the generated THz signal when the pump laser is tuned around the epsilon-near-zero (ENZ) region of ITO due to the pump laser field enhancement associated with the ENZ effect. The bandwidth of the THz signal generated from the ITO film can be over 3 THz, unrestricted by the phase-matching condition. This work offers a new possibility for broadband THz generation in a subwavelength thin film made of an ENZ material, with emerging physics not found in existing nonlinear crystals.

Abstract

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