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μs fluoride fiber laser with Bi thin film as a Q-switcher at 2879 nm for the first time. .... Bi thin film exhibit good consistency with that placed ...
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Functional Inorganic Materials and Devices

Broadband Nonlinear Optical Response of Single-Crystalline Bismuth Thin Film Lin Du, Donglin Lu, Jie Li, Ke Yang, Lingling Yang, Bin Huang, Jun Yi, Qian Yi, Lili Miao, Xiang Qi, Chujun Zhao, Jianxin Zhong, and Shuang-Chun Wen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10354 • Publication Date (Web): 20 Aug 2019 Downloaded from pubs.acs.org on August 21, 2019

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Broadband Nonlinear Optical Response of SingleCrystalline Bismuth Thin Film Lin Du,† ,▽ Donglin Lu,‡,▽ Jie Li,† Ke Yang,† Lingling Yang,† Bin Huang,† Jun Yi,† Qian Yi,† Lili Miao,† Xiang Qi,*,‡ Chujun Zhao,*,† Jianxin Zhong,‡ and Shuangchun Wen†

†Key

Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan

Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, China

‡ Hunan

Key Laboratory for Micro-Nano Energy Materials and Devices, Laboratory for

Quantum Engineering and Micro-Nano Energy Technology, and School of Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, China

KEYWORDS: Bismuth thin film, nonlinear optics, ultrafast photonics, broadband response, mid-infrared

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ABSTRACT: Bismuth (Bi), a topological material, where many interesting condensed matter phenomena have been observed, possesses unique physical properties when its thickness is reduced to thin film. Here, we prepared the highly stable, single-crystalline, continuous Bi thin film via vapor deposition (VD) method, and found that the Bi thin film can exhibit broadband, ultrafast nonlinear optical response with low saturable intensity ranging from near infrared to mid-infrared spectral range under strong excitation. Moreover, we demonstrated that the Bi thin film was favorable to act as a nonlinear pulse modulator towards high performance pulsed laser operating in optical communication and mid-infrared wavelengths. The experimental results highlight the prospects of Bi thin film as broadband pulsed modulators, and may open new avenues toward advanced Bi-based broadband photonic devices.

1. INTRODUCTION Semimetal bismuth (Bi), as the last element in group VA, is one of the most extensively studied elements in solid state physics due to its interesting physical properties,1-8 such as de Haas-van Alphen effect,4 quantum size confinement

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effect,5 quantum linear magnetoresistance,6 peculiar superconductivity,7 and possibly fractional quantum hall effect.8 Bi, with the electron configuration of 6s26p3 in the outmost shell, tends to form three bonds to close the shell. Therefore, every atom in bulk Bi has three σ bonds, and its nearest neighbors are arranged in the pyramid geometry of a triangle.9-11 Bi has an even number of valence electrons, indicating its close characteristic of an insulator. However, the material is usually deemed to be a semi-metallic prototype as the features of its energy bands (the overlap between the conduction band and the valence band), which contribute to the long Fermi wavelength (30 nm).12 With the reduced dimension, it has been theoretically proposed that when the thickness of the material is comparable to the Fermi wavelength, the quantum size effect can turn it from the semimetal into the semiconductor. From the experimental respect, the transition from the semimetal to the semiconductor is indeed present in the Bi thin film. The experiments showed that the semiconductor phase and the metal phase coexist in the Bi thin film (