Abstract
Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large χ(3). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.
Highlights
Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion
We demonstrate that the observed THG/SHG intensity ratio can be explained by quantum mechanical calculations based on finite-temperature many-body diagrammatic perturbation theory[39] and low-energy continuummodel Hamiltonians that include trigonal warping[35]
MoS2 flakes are produced by micromechanical cleavage (MC) of bulk MoS240 onto Si + 285 nm SiO2. 1L-MoS2 and bilayer (2L-MoS2) flakes are identified by a combination of optical contrast[41, 42] and Raman spectroscopy[43]
Summary
Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large χ(3) We explain this by calculating the nonlinear response functions of 1LMoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. This is nearly rotationally invariant[22,23,24,25,26,27,28,29], but with corrections due to trigonal warping It is because of these corrections[23, 26, 27], fully compatible with the D13h space group[1], but reducing the full rotational symmetry of the low-energy bands to a three-fold rotational symmetry[1], that a finite amplitude of nonlinear harmonic processes can exist at low photon energies in EN-MoS2. Similar to SHG14–18, the THG process is sensitive to the number of layers, their symmetry, relative orientation, as well as a Intensity (a.u.)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
