Two-dimensional semiconductors have recently emerged as promising materials for novel optoelectronic devices. In particular, they exhibit favorable nonlinear optical properties. Potential applications include broadband and ultrafast light sources, optical signal processing, and generation of nonclassical light states. The prototypical nonlinear process second harmonic generation (SHG) is a powerful tool to gain insight into nanoscale materials because of its dependence on crystal symmetry. Material resonances also play an important role in the nonlinear response. Notably, excitonic resonances critically determine the magnitude and spectral dependence of the nonlinear susceptibility. We perform ultrabroadband SHG spectroscopy of atomically thin semiconductors by using few-cycle femtosecond infrared laser pulses. The spectrum of the second harmonic depends on the investigated material, MoS2 or WS2, and also on the spectral and temporal shape of the fundamental laser pulses used for excitation. Here, we present a method to remove the influence of the laser by normalization with the flat SHG response of thin hexagonal boron nitride crystals. Moreover, we exploit the distinct angle dependence of the second harmonic signal to suppress two-photon photoluminescence from the semiconductor monolayers. Our experimental technique provides the calibrated frequency-dependent nonlinear susceptibility χ(2)(ω) of atomically thin materials. It allows for the identification of the prominent A and B exciton resonances, as well as excited exciton states.
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August 2019
Research Article|
August 01 2019
Supercontinuum second harmonic generation spectroscopy of atomically thin semiconductors
Torsten Stiehm
;
Torsten Stiehm
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
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Robert Schneider;
Robert Schneider
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
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Johannes Kern;
Johannes Kern
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
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Iris Niehues
;
Iris Niehues
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
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Steffen Michaelis de Vasconcellos
;
Steffen Michaelis de Vasconcellos
a)
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
a)Authors to whom correspondence should be addressed: michaelis@uni-muenster.de and Rudolf.Bratschitsch@uni-muenster.de
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Rudolf Bratschitsch
Rudolf Bratschitsch
a)
Institute of Physics and Center for Nanotechnology, University of Münster
, 48149 Münster, Germany
a)Authors to whom correspondence should be addressed: michaelis@uni-muenster.de and Rudolf.Bratschitsch@uni-muenster.de
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a)Authors to whom correspondence should be addressed: michaelis@uni-muenster.de and Rudolf.Bratschitsch@uni-muenster.de
Rev. Sci. Instrum. 90, 083102 (2019)
Article history
Received:
April 18 2019
Accepted:
July 11 2019
Connected Content
A companion article has been published:
Hexagonal boron nitride crystals help normalize second harmonic generation spectroscopy
Citation
Torsten Stiehm, Robert Schneider, Johannes Kern, Iris Niehues, Steffen Michaelis de Vasconcellos, Rudolf Bratschitsch; Supercontinuum second harmonic generation spectroscopy of atomically thin semiconductors. Rev. Sci. Instrum. 1 August 2019; 90 (8): 083102. https://doi.org/10.1063/1.5100593
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