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From weak to strong coupling of quantum emitters in metallic nano-slit Bragg cavities Ronen Rapaport

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The nanophotonics and quantum fluids group Acknowledgments Graduate Students: Nitzan Livneh Moshe Harats Itamar Rosenberg Ilai Schwartz Collaborations: Adiel Zimran, Uri Banin – Chemistry, Hebrew Univ. Ayelet Strauss, Shira Yochelis, Yossi Paltiel – Applied Physics Hebrew Univ. Loren Pfeiffer – EE, Princeton University Gang Chen – Bell Labs Support: -EU FP7 Marie Currie -ISF (F.I.R.S.T) -Wolfson Family Charitable Trust -Edmond Safra Foundation

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The nanophotonics and quantum fluids group Outline Extraordinary transmission (EOT) in nanoslit arrays EOT in nanoslit array exposed – Bragg Cavity Model Two level system in a cavity – the weak and strong coupling limits 3 Examples of control and manipulations of light-matter coupling: 1. WCL – linear: the Purcell effect and controlled directional emission of quantum dots 2. WCL – nonlinear: enhancement of optical nonlinearities: Two photon absorption induced fluorescence 3. SCL : Strong exciton-Bragg cavity mode coupling: Bragg polaritons

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The nanophotonics and quantum fluids group Resonant Extraordinary Transmission – output light intensity (at resonant wavelengths) larger than the geometrical ratio of open to opaque areas I out ( )/I in ( )>(open area)/(total area) Extraordinary Transmission (EOT) in subwavelength metal Hole/slit arrays Channeling of energy through the subwavelength openings!

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The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms TM EOT EOT of more than 5 Full numerical EM simulations: give full account ◦ No clear physical picture. E H TM

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The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TM E H Unit cell near field Surface Plasmon Polaritons (SPPs)

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The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TM E H Slit-Cavity resonances

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The nanophotonics and quantum fluids group EOT in nanoslit arrays: Possible mechanisms SPP modes TE EOT in TE with a thin dielectric layer No propagating (or standing) modes in subwavelength slits No SPP in TE polarization Waveguide modes E H TE

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The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Fabry-Perot Cavity: high resonant transmission with very highly reflective mirrors Standing optical modes constructive forward interference High transmission

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The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Inside the slit array: periodic Bragg (Bloch) modes for g > k, there are modes with m ≠ 0 Outside the slit array: For g > k, only the mode with m = 0 is propagating We can have Standing m ≠ 0 Bragg waves in the structure! Constructive interference with m=0 mode EOT I. Schwarz et al., preprint arXiv 1011.3713

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The nanophotonics and quantum fluids group Bragg Cavity Model for EOT Mapping to FP (waveguide) physics: Analytic condition for standing Bragg modes

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The nanophotonics and quantum fluids group Bragg Cavity Model for EOT TE TM Very good agreement with full numerical calculations. I. Schwarz et al., preprint arXiv 1011.3713

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The nanophotonics and quantum fluids group Bragg Cavities “one mirror” cavities easily integrated with various active/passive media small mode volume easily controllable Q-factor

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The nanophotonics and quantum fluids group At resonance, the relative strength of the Two Level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. TLS in a cavity – weak and strong coupling

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The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Weak coupling: g 0 <

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The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Strong coupling: g 0 >>max(κ,γ) The emission of a photon is a reversible process. Vacuum Rabi splitting TLS in a cavity – weak and strong coupling

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The nanophotonics and quantum fluids group At resonance, the relative strength of the Two level System (TLS) - cavity interaction is determined by: the photon decay rate of the cavity κ, the TLS non-resonant decay rate γ, the TLS–photon coupling parameter g 0. Strong coupling for excitons in planar microcavities – exciton- polaritons See J. Kasprzak, et al., Nature, 443 (2006) 409-414. “Dynamical” Exciton – polariton BEC in a microcavity TLS in a cavity – weak and strong coupling

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The nanophotonics and quantum fluids group 1. Weak coupling of Quantum dots to Bragg cavity modes – directional emission Nanocrystal quantum dots - NQDs Nanometric light source: ◦ Essentially a TLS ◦ Tunable emission wavelength ◦ High quantum efficiency Possible applications: ◦ Photodetectors ◦ Solar cells ◦ Lasing medium ◦ Single Photon sources

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The nanophotonics and quantum fluids group N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group samples Reference sample – quantum dots on a glass substrate Quantum dots in a polymer layer on the nano-slit array Quantum dot self-assembled monolayer on the nano-slit array N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Angular emission spectrum - Reference TE No angular dependence – as expected N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Angular emission spectrum – Nanoslit array TE TE emission Strong angular dependence, directional emission (follow EOT disp.) N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Directional emission with divergence of 3.4 o 20 fold emission enhancement to this angle Photon emission rate: The interaction with the structure is in the single quantum-dot (photon?) level Second order correlation measurements g (2) on the way 3.4 o N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Physical explanation – Purcell effect Purcell effect: The emission rate of a dipole in a cavity into a cavity mode is enhanced. Our structure acts as a Bragg cavity with an eigenmode at 0 o → stronger emission to 0 o Near field in 0 o (structure mode) Near field in 15 o

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The nanophotonics and quantum fluids group Physical explanation – Purcell effect The dipole emission rate into a cavity mode is given by 3.4 o Experimental values: Numerical model: Despite a low Q factor, the nanoslit array significantly enhances the emission to 0 o due to a Small modal volume N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Angular emission spectrum – QD monolayer N. Livneh et al., Nano Letters(2011)

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The nanophotonics and quantum fluids group Towards directional emission of a single QD -

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The nanophotonics and quantum fluids group 2. enhancement of optical nonlinearities: Two photon absorption induced fluorescence Experimental configurationExcitation and Nanocrystal Quantum Dots Photoluminescence Two photon upconversion process M. Harats et al., Optics Express (2011)

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The nanophotonics and quantum fluids group Two photon absorption induced fluorescence - the intensity enhancement factor in the nanoslit array Using the resonant enhancement of EM fields in the nanoslit array results with The induced upconversion is: Glass substrate Polymer layer Al da H h M. Harats et al., Optics Express (2011) QD absorption:

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The nanophotonics and quantum fluids group TPA and induced upconverted fluorescence in semiconductor NQDs in TE polarization in metallic nanoslit arrays with a maximal enhancement of ~400 Two photon absorption induced fluorescence M. Harats et al., Optics Express (2011)

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The nanophotonics and quantum fluids group 3. Strong exciton-Bragg cavity mode coupling: Bragg exciton-polaritons in GaAs QW’s The signature of strong coupling: vacuum Rabi splitting (avoided crossing) Second order bragg resonance

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The nanophotonics and quantum fluids group TM Calculated angular absorption spectrum – no excitons no excitons

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The nanophotonics and quantum fluids group Angular absorption spectrum – with excitons Clear vacuum Rabi Splitting (~4meV). Clear avoided crossings TM

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The nanophotonics and quantum fluids group Angular absorption spectrum – TE TE

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The nanophotonics and quantum fluids group Thank you

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Experimental results - wavelength dependence Using Dynamical Diffraction (1), near-field intensities are extracted. An averaged unit cell enhancement is calculated by: (1) M. M. J. Treacy, Phys. Rev. B, 66(19):195105, Nov 2002. What’s happening in the wavelengths noted by the red circles?

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Analysis As we used a pulse with a spectral width ( ), the enhancement per wavelength is taken into account: This is good agreement between the experimental and theoretical results

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