Abstract
In this work, we demonstrate an approach to study exciton-polaritons supported by transition metal dichalcogenide monolayers coupled to an unstructured planar waveguide below the light line. In order to excite and probe such waves propagating along the interface with the evanescent fields exponentially decaying away from the guiding layer, we employ a hemispherical ZnSe solid immersion lens (SIL) precisely positioned in the vicinity of the sample. We visualize the dispersion of guided polaritons using back focal (Fourier) plane imaging spectroscopy with the high-NA objective lens focus brought to the center of SIL. This results in the effective numerical aperture of the system exceeding an exceptional value of 2.2 in the visible range. In the experiment, we study guided polaritons supported by a WS2 monolayer transferred on top of a Ta2O5 plane-parallel optical waveguide. We confirm room-temperature strong light-matter coupling regime enhanced by ultra-low intrinsic ohmic and radiative losses of the waveguide. Note that in the experiment, total radiative losses can be broadly tuned by controlling SIL-to-sample distance. This gives a valuable degree of freedom for the study of polariton properties. Our approach lays the ground for future studies of light-matter interaction employing guided modes and surface waves.
Highlights
Rapid development of the field of all-optical devices such as optical switches and transistors boosts the search for highly nonlinear optical systems
We use a high numerical aperture objective lens (Mitutoyo, M Plan Apo HR, 100×, NAobj = 0.9) in combination with ZnSe prism coupled to the sample with a precisely controlled air gap in Otto geometry [10]
The sample was attached to a piezo positioner, which allowed for precise control of the solid immersion lens (SIL)-tosample gap
Summary
Rapid development of the field of all-optical devices such as optical switches and transistors boosts the search for highly nonlinear optical systems. We use a high numerical aperture objective lens (Mitutoyo, M Plan Apo HR, 100×, NAobj = 0.9) in combination with ZnSe (refractive index nZnSe ≈ 2.5 in the visible range) prism coupled to the sample with a precisely controlled air gap in Otto geometry [10].
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