Characterizing the nonlinear optical properties of 2d materials by double 4f nonlinear imaging system with phase object and four-wave-mixing microscopy

Two-dimensional (2D) materials have attracted considerable research attention in the past two decades due to their intriguing thermal, mechanical, and optical properties. A deeper understanding of the structure-property relationship of 2D material is essential for future development of functional devices. Characterizing the nonlinear optical (NLO) response of 2D materials is of great importance for material analysis and device engineering. In this chapter, we highlight the recent progress in the third-order NLO measurement methods of 2D materials, with a focus on results with microscopy. First, we summarize the principles of nonlinear optics and common NLO characterization methods in 2D material research. Second, we introduce the double 4f nonlinear imaging system with phase object (NIT-PO) method. The history and theoretical underpinnings of the technique are briefly discussed. Third, the four-wave-mixing microscopy method is described, and the recent experimental data are highlighted. Finally, we provide a perspective on the trends and challenges of NLO measurement technique for 2D material research.