All-optically generating and monitoring interlayer expansion of layered GaSe via in situ second harmonic generation

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Interlayer-distance engineering can provide a degree of freedom to tailor the intrinsic physical properties of 2D layered semiconductors and van der Waals heterostructures. In this Letter, we report an all-optical technique to simultaneously generate and monitor interlayer expansions of multilayer GaSe lattice via optical second harmonic generation (SHG). Heat induced by the absorption of fundamental laser can trigger interlayer expansion, while intensity change of SHG caused by mediated superposition of SHG field in expanded layers can monitor the level of interlayer expansion. Our results open an avenue to all-optically engineer interlayer distance of 2D layered semiconductors.