Nonlinear Optical Response of a WS2 Monolayer at Room Temperature upon Multicolor Laser Excitation,ACS Photonics

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Nonlinear Optical Response of a WS2 Monolayer at Room Temperature upon Multicolor Laser Excitation
ACS Photonics ( IF 6.5 ) Pub Date : 2021-01-11 , DOI: 10.1021/acsphotonics.0c01567
Javier Hernandez-Rueda ₁ , Marc L Noordam ₁ , Irina Komen ₁ , L Kuipers ₁

Affiliation

Currently, the nonlinear optical properties of 2D materials are attracting the attention of an ever-increasing number of research groups due to their large potential for applications in a broad range of scientific disciplines. Here, we investigate the interplay between nonlinear photoluminescence (PL) and several degenerate and nondegenerate nonlinear optical processes of a WS₂ monolayer at room temperature. We illuminate the sample using two femtosecond laser pulses at frequencies ω₁ and ω₂ with photon energies below the optical bandgap. As a result, the sample emits light that shows characteristic spectral peaks of the second-harmonic generation, sum-frequency generation, and four-wave mixing. In addition, we find that both resonant and off-resonant nonlinear excitation via frequency mixing contributes to the (nonlinear) PL emission at the A-exciton frequency. The PL exhibits a clear correlation with the observed nonlinear effects, which we attribute to the generation of excitons via degenerate and nondegenerate multiphoton absorption. Our work illustrates a further step toward understanding the fundamental relation between parametric and nonparametric nondegenerate optical mechanisms in transition-metal dichalcogenides. In turn, such understanding has great potential to expand the range of applicability of nonlinear optical processes of 2D materials in different fields of science and technology, where nonlinear mechanisms are typically limited to degenerate processes.

中文翻译：

室温下 WS2 单分子层在多色激光激发下的非线性光学响应

目前，二维材料的非线性光学特性因其在广泛科学学科中的巨大应用潜力而吸引了越来越多研究小组的关注。在这里，我们研究了室温下 WS ₂单层的非线性光致发光 (PL) 与几种简并和非简并非线性光学过程之间的相互作用。我们使用频率为 ω ₁和 ω ₂且光子能量低于光学带隙的两个飞秒激光脉冲照射样品。结果，样品发出的光显示出二次谐波生成、和频生成和四波混频的特征光谱峰值。此外，我们发现通过混频实现的谐振和非谐振非线性激励都有助于 A 激子频率下的（非线性）PL 发射。 PL 与观察到的非线性效应表现出明显的相关性，我们将其归因于通过简并和非简并多光子吸收产生激子。我们的工作进一步说明了理解过渡金属二硫属化物中参数和非参数非简并光学机制之间的基本关系。反过来，这种理解具有扩大二维材料非线性光学过程在不同科学技术领域的适用范围的巨大潜力，其中非线性机制通常仅限于简并过程。

更新日期：2021-02-17

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