Browsing by Author "Rostami, Habib"

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  • Probing Electronic States in Monolayer Semiconductors through Static and Transient Third-Harmonic Spectroscopies
    (2022-01-20) Wang, Yadong; Iyikanat, Fadil; Rostami, Habib; Bai, Xueyin; Hu, Xuerong; Das, Susobhan; Dai, Yunyun; Du, Luojun; Zhang, Yi; Li, Shisheng; Lipsanen, Harri; García de Abajo, F. Javier; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, various relevant electronic states in monolayer MoS2, such as multiple excitonic Rydberg states and free-particle energy bands are probed with a high relative contrast of up to >= 200 via broadband (from approximate to 1.79 to 3.10 eV) static third-harmonic spectroscopy (THS), which is further supported by theoretical calculations. Moreover, transient THS is introduced to demonstrate that third-harmonic generation can be all-optically modulated with a modulation depth exceeding approximate to 94% at approximate to 2.18 eV, providing direct evidence of dominant carrier relaxation processes associated with carrier-exciton and carrier-phonon interactions. The results indicate that static and transient THS are not only promising techniques for the characterization of monolayer semiconductors and their heterostructures, but also a potential platform for disruptive photonic and optoelectronic applications, including all-optical modulation and imaging.
  • Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers
    (2017-12-01) Säynätjoki, Antti; Karvonen, Lasse; Rostami, Habib; Autere, Anton; Mehravar, Soroush; Lombardo, Antonio; Norwood, Robert A.; Hasan, Tawfique; Peyghambarian, Nasser; Lipsanen, Harri; Kieu, Khanh; Ferrari, Andrea C.; Polini, Marco; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.