Quantum interference in second-harmonic generation from monolayer WSe2

Abstract

2 A hallmark of wave-matter duality is the emergence of quantum-interference phenomena when an electronic transition follows different trajectories. Such interference results in asymmetric absorption lines such as Fano resonances 1 , and gives rise to secondary effects like electromagnetically induced transparency (EIT) when multiple optical transitions are pumped 2-5 . Few solid-state systems show quantum interference and EIT 5-11 , with quantum-well intersubband transitions in the IR 12,13 offering the most promising avenue to date to devices exploiting optical gain without inversion 14,15 . Quantum interference is usually hampered by inhomogeneous broadening of electronic transitions, making it challenging to achieve in solids at visible wavelengths and elevated temperatures. However, disorder effects can be mitigated by raising the oscillator strength of atom-like electronic transitionsexcitonswhich arise in monolayers of transition-metal dichalcogenides (TMDCs) 16,17 . Quantum interference, probed by second-harmonic generation (SHG) 18,19 , emerges in WSe2, without a cavity, splitting the SHG spectrum. The splitting exhibits spectral anticrossing behaviour, and is related to the number of Rabi flops the strongly driven system undergoes. The SHG powerlaw exponent deviates strongly from the canonical value of 2, showing a Fano-like wavelength dependence which is retained at room temperature. The work opens opportunities in solid-state quantum-nonlinear optics for optical mixing, gain without inversion and quantum-information processing.We consider the wavelength dependence of SHG from monolayer WSe2 crystals as sketched in Fig. 1a. Under excitation at 724 nm with pulses of 80 fs length at 80 MHz repetition rate, Fig. 1b reveals two peaks in the SHG spectrum, at 360 nm and 364 nm,

Twist-tailoring Coulomb correlations in van der Waals homobilayers

“…1a) are stamped on top of each other. Before the transfer, the crystallographic orientations of the layers are determined by polarization-resolved second-harmonic generation 15,31 . The component of the second harmonic I 2ω,|| polarized parallel to the near-infrared pump laser indicates the armchair directions of each monolayer (inset Fig.…”

“…Second-harmonic generation. The twist angle θ was determined for each BL by polarization-resolved second-harmonic generation (SHG) under rotation of the plane of polarization 31 . Isolated monolayer regions of the structure were excited by a linearly-polarized femtosecond mode-locked Ti:sapphire laser and the intensity of the SHG was recorded.…”

Nonlinear optics of two‐dimensional transition metal dichalcogenides

“…The optical limiting performance is dependent on the layer number and the excitation wavelength due to the layer number dependent band gap . Furthermore, Lin et al reported a quantum interference in SHG of monolayer WSe 2 , which splits the frequency‐doubled laser spectrum and shows a Fano‐like resonance . The quantum interference is attributed to the strong oscillation strength of monolayer TMDs and their work opens opportunities in solid‐state quantum‐nonlinear optics.…”

Controlling the non-linear optical properties of MgO by tailoring the electronic structure

“…For example, perturbative and non-perturbative high harmonics have been generated from the surface states of solids which shows the suppression of higher harmonics in bulk material due to lack of phase matching [1]. For an in-depth theoretical and experimental treatment of SHG, we refer the reader to the following works [2][3][4][5][6][7]. Practical uses of SSHG are widespread, including SHG spectroscopy for imaging to investigate the bio-molecular interactions at interfaces [8], optical imaging [9,10], characterization of the interface of semiconductors [11], and near-field and far-field optical microscopy of microelectronics structures [12].…”