Harmonic Generation in Low-Dimensional Materials

Low-dimensional materials (LDMs) provide an unprecedented avenue having the potential to disruptively revolutionize the information and communication technologies. The rise of nonlinear photonics in LDMs began about in 2009 and has now become an important research direction. While harmonic generation, a widely studied nonlinear optical effect, can be a powerful probe to low-dimensional physics, it may also find applications in bioimaging, optical signal processing, and novel coherent light sources. In this work, the state-of-the-art advances in harmonic generation are reviewed in a range of emerging LDMs. The criteria of chiral selection rules for the second and third harmonic generations are also provided. In particular, different strategies to tune and enhance harmonic generation in LDMs are discussed, including excitonic effects, interlayer twisting angle, electric field, and cavity resonance among others. It is believed that harmonic generation in LDMs will continue to grow, thus lying the basis for practical applications.