Säynätjoki Antti, Karvonen Lasse, Rostami Habib, Autere Anton, Mehravar Soroush, Lombardo Antonio, Norwood Robert A, Hasan Tawfique, Peyghambarian Nasser, Lipsanen Harri, Kieu Khanh, Ferrari Andrea C, Polini Marco, Sun Zhipei
Department of Electronics and Nanoengineering, Aalto University, Tietotie 3, FI-02150, Espoo, Finland.
Institute of Photonics, University of Eastern Finland, Yliopistokatu 7, FI-80100, Joensuu, Finland.
Nat Commun. 2017 Oct 12;8(1):893. doi: 10.1038/s41467-017-00749-4.
Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS (1L-MoS): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS is approximately three times higher than that for graphene, which was reported to have a large χ . We explain this by calculating the nonlinear response functions of 1L-MoS with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.Harmonic generation is a nonlinear optical process occurring in a variety of materials; the higher orders generation is generally less efficient than lower orders. Here, the authors report that the third-harmonic is thirty times stronger than the second-harmonic in monolayer MoS2.
诸如谐波产生等非线性光学过程在各种应用中具有重大意义，例如显微镜技术、治疗以及频率转换。然而，由于高阶非线性过程的固有响应较弱，高阶谐波转换的效率通常远低于低阶谐波转换。在此，我们报道了单层二硫化钼（1L-MoS）中存在超强光学非线性：其三阶谐波比二阶谐波强30倍，且四阶谐波与二阶谐波相当。1L-MoS的三阶谐波产生效率约为石墨烯的三倍，据报道石墨烯具有较大的χ。我们通过使用连续模型哈密顿量和量子力学图解微扰理论计算1L-MoS的非线性响应函数来解释这一现象，突出了三角翘曲的作用。预计在所有其他过渡金属二硫属化物中也会有类似效应。我们的结果为基于层状材料的高效谐波产生在显微镜技术和成像等应用方面铺平了道路。谐波产生是在多种材料中发生的非线性光学过程；高阶谐波产生通常比低阶谐波产生效率更低。在此，作者报道在单层二硫化钼中三阶谐波比二阶谐波强三十倍。
