Ultrafast and Nonlinear Photonics in 2D Hybrid Perovskites

I. ABDELWAHAB; K. LENG; R. F. OULTON; M. P. NIELSEN; X. CHI; K. P. LOH; G. GRINBLAT; P. DICHTL; A. RUSYDI; S. A. MAIER

Conferencia; Nanophotonics of 2D Materials; 2020

Boosting ultrafast and nonlinear optical effects at the nanoscale has been a subject of growing interest due to the promise of a wide variety of practical applications such as all-optical information processing devices and photovoltaics. However, efficient ultrafast and nonlinear optical nano-components are still far from realization, highlighting the need for novel alternatives. 2D hybrid organic-inorganic Ruddlesden-Popper perovskites (RPPs) have a natural multi-quantum-wells structure with very high exciton binding energies and oscillator strengths. Under resonant exciton excitation, the large induced transition dipole moment is expected to highly enhance third-order nonlinear effects [1]. Furthermore, such nonlinear effects can give rise to ultrafast all-optical modulation at femtosecond time scales [2].In this work, we investigate the nonlinear and ultrafast optical response of 2D perovskite nanosheets mechanically exfoliated from different high-quality lead halide RPP single crystals [3,4]. We observe ultra-strong third-harmonic generation (THG) with maximum conversion efficiencies close to 0.01% [3]. The THG emission is resonantly enhanced at the excitonic bandgap energy of the 2D RPP crystals and can be tuned from the violet to the red by selecting the RPP homologue with the requisite resonance. Due to signal depletion effects and phase-matching conditions, the strongest nonlinear response is achieved for thicknesses below 100 nm. In addition, we also study the ultrafast dynamics of the 2D RPP thin flakes through pump-probe spectroscopy in the 600-1000 nm wavelength range using sub-10 fs pulses [4]. We find that, under sub-bandgap excitation, a perovskite sheet allows up to ⁓2% reflectivity modulation within a 20-fs period. The ultrafast behaviour is attributed to the third-order nonlinear optical Kerr effect (OKE) and two-photon absorption (TPA), with TPA acting as a counteracting effect that prevents an even higher modulation, as shown by numerical simulations. When the excitation is resonant with the excitonic absorption, the ultrafast nature of the nonlinear response is lost due to the presence of linear absorption creating long-lived free carriers. Our results show the promise of 2D RPP crystals as on-chip optical nonlinear components, as well as their potential for nanoscale ultrafast all-optical switching, and lay the foundations for the search of more efficient ultrafast nanomaterials.[1] I. Abdelwahab, P. Dichtl, G. Grinblat, K. Leng, X. Chi, I.-H. Park, M. P. Nielsen, R. F. Oulton, K. P. Loh, S. A. Maier, Advanced Materials 31, 1902685 (2019).[2] G. Grinblat, M. P. Nielsen, P. Dichtl, Y. Li, R. F. Oulton, S. A. Maier. Science Advances 5, eaaw3262 (2019).[3] I. Abdelwahab, G. Grinblat, K. Leng, Y. Li, X. Chi, A. Rusydi S. A. Maier, K. P. Loh, ACS Nano 12, 644 (2018).[4] G. Grinblat, I. Abdelwahab, M. P. Nielsen, P. Dichtl, K. Leng, R. F. Oulton, K. P. Loh, S. A. Maier, ACS Nano 13, 9504 (2019).