Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 84: Gerhard Ertl Young Investigator Award Competition

O 84.2: Talk

Thursday, March 20, 2025, 11:00–11:30, H24

Nano-optical imaging of grating-coupled waveguide modes in 3R-MoS₂ — •Fabian Mooshammer¹, Xinyi Xu², Chiara Trovatello², P. James Schuck², and D. N. Basov³ — ¹Regensburg Center for Ultrafast Nanoscopy (RUN), University of Regensburg, Regensburg, Germany — ²Department of Mechanical Engineering, Columbia University, New York, USA — ³Department of Physics, Columbia University, New York, USA

Waveguide modes in thin slabs of van der Waals crystals serve as reliable probes of the anisotropic dielectric response of the material and also hold great potential for the implementation of on-chip optical elements. Here, we show that near-field imaging can resolve the propagation patterns of waveguide modes, which encode the birefringence of transition metal dichalcogenides. We use a laser patterning procedure to write grating structures into 3R-MoS₂ crystals with grooves as sharp as 250 nm. Spatial maps of the scattered electric field in the vicinity of the gratings reveal a directional, polarization-splitting outcoupling of waveguide modes, which is in line with finite element simulations. Experiments over a range of near-infrared photon energies provide key parameters for waveguide second-harmonic generation. The latter is finally demonstrated by grating-coupling femtosecond pulses into the slabs. In the future, nano-optical imaging may be used to directly capture the frequency conversion process during the propagation of the modes. Our work demonstrates the feasibility of compact frequency converters and examines the tunings knobs that enable optimized coupling into layered waveguides.

Keywords: 3R-MoS2; waveguide; near-field microscopy; grating; SNOM