Probing Electronic States in Monolayer Semiconductors through Static and Transient Third‐Harmonic Spectroscopies

Abstract

Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, we probe various relevant electronic states in monolayer MoS2, such as multiple excitonic Rydberg states and free-particle energy bands, with a high relative contrast of up to ≳200 via broadband (from ~1.79 to 3.10 eV) static third-harmonic spectroscopy, which is further supported by theoretical calculations. Moreover, we introduce transient third-harmonic spectroscopy to demonstrate that third-harmonic generation can be alloptically modulated with a modulation depth exceeding ~94% at ~2.18 eV, providing direct evidence of dominant carrier relaxation processes, associated with carrier-exciton and carrierphonon interactions. Our results indicate that static and transient third-harmonic spectroscopies are not only promising techniques for the characterization of monolayer semiconductors and their heterostructures, but also a potential platform for disruptive photonic and optoelectronic applications, including all-optical modulation and imaging.

Coherent modulation of chiral nonlinear optics with crystal symmetry

“…Such a high modulation depth and ultra-fast response features make our approach promising for ultra-fast nanophotonics. We then analyze the conversion efficiency ~1.6 × 10 −7 % and the third-order susceptibility ~1.7 × 10 −19 m 2 /V 2 when the incident beams are at ~1560 nm (Details about the calculation and at other incident wavelengths are given in Section 6 of SI), which are comparable to previous results (~10 −19 m 2 /V 2 ) 15 , 20 , 32 , 33 .

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“…As a common and widely used third-order nonlinear optical process, third-harmonic generation (THG) is always present in a large range of materials (such as silica 8 , metamaterials 9 , 10 , and 2D materials 11 – 16 ), in contrast to the second-harmonic generation (SHG) that only exists in non-centrosymmetric materials 5 . Recently, all-optical modulations of THG in hybrid micro-systems 17 , 18 , gold metasurfaces 19 , and 2D layered materials 20 , 21 have been explored. However, these all-optical modulation methods typically involve carrier relaxation, and thus are naturally incoherent with a relatively slow modulation speed (>~ps), a typical modulation depth of ~90% 20 , 21 , and polarization non-selectivity.…”

“…Recently, all-optical modulations of THG in hybrid micro-systems 17 , 18 , gold metasurfaces 19 , and 2D layered materials 20 , 21 have been explored. However, these all-optical modulation methods typically involve carrier relaxation, and thus are naturally incoherent with a relatively slow modulation speed (>~ps), a typical modulation depth of ~90% 20 , 21 , and polarization non-selectivity. Therefore, novel all-optical modulation strategies with high performance in speed and modulation depth, and polarization selection capability are thus of great importance.…”

Parametric Nonlinear Optics with Layered Materials and Related Heterostructures

“…A first approach is to quench the NLO response of TMDs and graphene by above-bandgap photoexcitation and Pauli blocking. [73,[182][183][184] This method is significantly faster compared [188] Copyright 2021, American Chemical Society. b,c) All-optical modulation on THG in 1L graphene.…”

Second Harmonic Helicity and Faraday Rotation in Gated Single-Layer 1T$'$-WTe$_2$

“…Strong and diverse forms of nonlinear response in 2D materials are drawing attention for applications in all-optical modulators [33][34][35][36][37]. Especially, a strong nonlinear Hall response has been measured in single and bilayer of WTe 2 that can be described in terms of the Fermi surface average of the Berry curvature derivative, the so called Berry curvature dipole [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54].…”