Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Z. W. acknowledges scholarship support from NUS Graduate School for Integrative Sciences & Engineering (NGS). Z.D. and J.K.W.Y. acknowledge the funding support from the Agency for Science, Technology and Research (A*STAR) Young Investigatorship (grant number 0926030138), SERC (grant number 092154099), the National Research Foundation (grant number NRF-CRP 8-2011-07), A*STAR Pharos Program (Grant No. 1527300025), and A*STAR-JCO under project number 1437C00135. C.-W.Q acknowledges the financial support from A*STAR Pharos Program (Grant No. 152 70 00014, with Project No. R-263-000-B91-305). Z. W. and A.T.S.W. acknowledges the funding support from MOE Tier 2 grant R 144-000-382-112 and facility support from NUS Center for Advanced 2D Materials. S.A.M. acknowledges the EPSRC Reactive Plasmonics Programme Grant (EP/M013812/1), the Royal Society, and the Lee-Lucas Chair in Physics. L.-J.L. acknowledges support from KAUST (Saudi Arabia) and Taiwan Consortium of Emergent Crystalline Materials (TCECM). G.E. acknowledges Singapore National Research Foundation, Prime Minister s Office, Singapore, for funding the research under its Medium-sized Centre program as well as NRF Research Fellowship (NRF-NRFF2011-02).