Active tuning of spontaneous emission by. Mie-resonant dielectric metasurfaces: Supporting. Information

Transcription

1 Active tuning of spontaneous emission b Mie-resonant dielectric metasurfaces: Supporting Information Justus Bohn, Tobias Bucher, Katie. Chong, Andrei Komar, Duk-Yong Choi, Dragomir N. Neshev, Yuri S. Kivshar, Thomas Pertsch, and Isabelle Staude, Institute of Applied Phsics, Abbe Center of Photonics, Friedrich Schiller Universit Jena, Jena, German Nonlinear Phsics Centre, Research School of Phsics and ngineering, The Australian National Universit, Canberra, 2601 ACT, Australia Laser Phsics Centre, Research School of Phsics and ngineering, The Australian National Universit, Canberra, ACT 2601, Australia -mail: isabelle.staude@uni-jena.de Number of pages: 8 Number of figures: 5 S1

2 Details of the white-light spectroscop setup MB Illumination Signal LH AS TL OB ST CD FS LP AS CL LH CL AS LP FS CD Lamp Housing Collector Aperture Stop Linear Polarizer Field Stop Condenser MB ST OB TL CM SP Microscope Bod Sample Table Objective Tube Lens Camera Spectrometer Sample hea ng design CM SP Figure S1: Schematic of the custom white-light spectroscop setup used for the transmission measurements. The inset shows a photograph of the heating assembl. Fig. S1 shows a sketch of the optical setup used for temperature dependent transmittance measurements. The heating mechanism (see inset) for our proof-of-principle eperiments is utilizing a heating resistor (WLWYN, WH10 15R JI) and a PT-100 temperature sensor placed together with the metasurface (MS) LC-cell on a Al 2 O 3 substrate. We connected these to a ILX Lightwave LDT-5980 high power temperature controller. For the PL measurements we used the commerciall available Picoquant MicroTime-200 sstem, implementing a standard confocal fluorescence microscope. Mode profiles for the infiltrated metasurface cell In order to verif the swapping of the spectral positions of the electric (D) and magnetic (MD) dipole resonances after liquid crstal (LC) infiltration with respect to the uninfiltrated case, we numericall calculated the transmittance spectra and mode profiles of the LC in- S2

3 filtrated metasurface. These results are shown in Fig. S2 and Fig. S3 for the nematic and the isotropic case, respectivel. For the nematic case, we modelled the LC as an anisotropic medium with ne = 1.72 and n0 = 1.51,1 where the anisotrop ais of the LC coincides with one of the lattice directions to mimic the in-plane LC alignment. In the nematic case, the mode profile of the resonance at longer wavelength ehibits electric dipolar characteristics (compare e.g. Decker et al.2 ), while that of the shorter wavelength resonance shows the tpical features of a magnetic dipole mode. For the isotropic case, these characteristics are preserved, but the spectral separation between the modes is strongl reduced. (b) (a) nematic Magnetic dipole lectric dipole z H H B z Figure S2: (a) Numericall calculated linear-optical transmittance spectra of the metasurface embedded in nematic. The incident electric field is oriented in -direction, parallel to the anisotrop ais of the LC. (b) The corresponding calculated field distributions at the D and MD resonance wavelengths. S3

4 (b) (a) isotropic Magnetic dipole lectric dipole z H H B z Figure S3: (a) Numericall calculated linear-optical transmittance spectra of the metasurface embedded in isotropic LC. The incident electric field is oriented in -direction. (b) Corresponding calculated field distributions at the D and MD resonance wavelengths. Note that the resonances are getting ver narrow due to long-range in-plane interactions as the resonances are shifted spectrall close to the Wood anomal in numerical simulations. Such behaviour was observed in several previous works studing arras of scatterers.3 5 In our simulations we use a simplified model for the LC, approimating it as a perfectl homogeneous anisotropic medium without an scattering losses. In eperiment, however, the LC will introduce scattering losses due to more comple alignments of the LC molecules near the nanoresonators. These arise due to the nanostructured topograph of the metasurface and are not taken into account in numerical simulations. Thus, long-range interactions will be suppressed, leading to broader resonances6 in our eperiment as compared to the numerical spectra. Another factor contributing to the broadening of the resonances in the eperimental spectra is the finite numerical aperture of the emploed objective lens, which is not taken into account in the numerical simulations. S4

5 Numerical simulations based on the reciprocit principle Numerical studies of emission enhancement mediated b a nanostructure tpicall follow the strateg of placing a point(-dipole) emitter in the vicinit of that nanostructure and monitoring the change in total emitted power. However, this method cannot readil be applied to periodic problems as placing an emitter inside the structures unit cell would model the case of an arra of perfectl coherent emitters. Therefore, to provide a qualitative estimate for the tuning of the emission spectra, we follow a method based on the reciprocit principle as previousl demonstrated for light-emitting dielectric metasurfaces b Vaskin et al.. 7 In this work, directional emission from a sample consisting of a metasurface situated on a fluorescent glass substrate was modelled b introducing artificial losses to a thin laer of glass below the metasurface. B reciprocit, the absorption in this laer can then be treated as a measure of the total emitted power. Note that this method takes neither the quantum efficienc of the emitters nor their discrete nature into account. In our simulations, we introduced a 50 nm thick laer with weak absorption (refractive inde of n= i 0.001) beneath the silicon nanodisks as shown in Fig. S4 (a). The linear transmittance spectra as well as the change in the total absorption due to the artificial laer for the nematic and isotropic case are shown in Fig. S4 (b). The results are calculated for a simplified case of a lattice constant of 535 nm in order to avoid spectral overlap of the Mie-tpe and Wood-tpe resonances in our simulations. Clearl, the change in total absorption, and hence total emission, shows pronounced peaks at the spectral positions of the Mie-tpe resonances. While two distinct emission peaks can be observed in the nematic case, their spectral separation gets strongl reduced in the isotropic case leading to a single broad emission peak. In the isotropic case, the two dipolar Mie-tpe resonances are close to the Hugens-overlap resulting in deviations of the spectral emission line shape compared to the respective linear transmittance spectrum. Note further that the spectral separation of S5

6 electric and magnetic Mie-tpe resonances found in our simulations for the nematic case is significantl larger than the separation observed in the eperimental results (cf. Fig. 3), which can be eplained b the imperfect alignment of the liquid crstals close to the nanodisks. Figure S4: (a) Sketch of the considered simulation geometr; (b) Simulated transmission (dashed lines) and emission (solid lines) spectra of an eemplar silicon nanoclinder metasurface showing two transmittance dips in the nematic case (blue lines) and a single transmittance dip in the isotropic case (red lines). Temperature dependent emission spectra Fig. S5 shows emission spectra and emission contrast, respectivel, for a range of temperatures, clearl demonstrating that the switching shows the strongest dnamics in a narrow temperature interval, as characteristic for a phase transition. S6

7 (a) mission (counts) Wavelength (nm) (b) m / m (25 C) (%) C 63 C 60 C 56 C 53 C 49 C 46 C 42 C 39 C 35 C 32 C 28 C C Wavelength (nm) 67 C 63 C 60 C 56 C 53 C 49 C 46 C 42 C 39 C 35 C 32 C 28 C 25 C Figure S5: (a) Temperature dependent emission spectrum and (b) emission contrast (solid lines) of the silicon nanoclinder metasurface after integration into the LC cell. Note that for the emission tuning measurements we observe a decrease of the LC phase transition temperature b about 10 C as compared to the transition temperature observed in transmission measurements. This can likel be attributed to laser-induced heating of the sample for the estimated ecitation power flu of 10 5 W/cm 2. Importantl, while the resonance positions of the silicon metasurface themselves depend on temperature, the effect is relativel weak, 0.1 nm red-shift per degree. 8 The metasurface heating results in a similar red-shift of a few nanometers for both the electric and magnetic dipolar resonance, while in our eperiments, the resonances are spectrall shifted in opposite directions, bringing them closer together. We can therefore conclude that the dnamics of the sstem is dominated b the change of LC phase, rather than b the heating (optical or other) of the silicon nanoresonators. References (1) Li, J.; Wen, C.-H.; Gauza, S.; Lu, R.; Wu, S.-T. J. Disp. Technol. 2005, 1, S7

8 (2) Decker, M.; Staude, I.; Falkner, M.; Dominguez, J.; Neshev, D. N.; Brener, I.; Pertsch, T.; Kivshar, Y. S. Adv. Opt. Mat. 2015, 3, (3) Auguié, B.; Barnes, W. L. Phs. Rev. Lett. 2008, 101, (4) Kravets, V. G.; Schedin, F.; Grigorenko, A. N. Phs. Rev. Lett. 2008, 101, (5) Babicheva, V..; vlukhin, A. B. Laser Photon. Rev. 2017, 11, (6) Yang, Y.; Kravchenko, I. I.; Briggs, D. P.; Valentine, J. Nat. Commun. 2014, 5, (7) Vaskin, A.; Bohn, J.; Chong, K..; Bucher, T.; Zilk, M.; Choi, D.-Y.; Neshev, D. N.; Kivshar, Y. S.; Pertsch, T.; Staude, I. ACS Photonics 2018, 5, (8) Rahmani, M.; Xu, L.; Miroshnichenko, A..; Komar, A.; Camacho-Morales, R.; Chen, H.; Zárate, Y.; Kruk, S.; Zhang, G.; Neshev, D. N.; Kivshar, Y. S. Adv. Funct. Mater. 2017, 27, S8