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84 Nanophotonics Trapping a single atom with a fraction of a photon Arjon van Lange, A.J.vanLange@uu.nl, phone: 030 - 253 28 01 Sponsor: FOM, since May 2011 Supervisor: Dr. Dries van Oosten Laser cooling, band structure calculations, SNOM, optical tweezers Light-matter interactions become increasingly more important. Already, they determine how we perceive the world. In the future photonics is expected to succeed electronics, because photons are simply faster than electrons. The emission and absorption of light is inherently quantum mechanical, because transitions between quantum eigenstates of atoms are involved. The quantum nature of light becomes apparent in an optical cavity. Therefore, the simplest system in which to investigate the quantum nature of light-matter interaction, is an atom interacting with light inside an optical cavity. We trap an atom in the light field of a photonic crystal nanocavity. The mode volume of the cavity is comparable to the polarization volume of the atom. Therefore the proximity of an atom changes the cavity resonance frequency. In case of fixed frequency laser pumping of the cavity, the distance of the atom to the cavity affects the cavity light intensity and thereby the optical force on the atom. The atom will be trapped at ~ 100 nm from the surface for proper choice of frequencies. Remarkably, the light intensity required to trap the atom corresponds to only a fraction of a photon [1]. In the experimental setup (figure 1a) a cold rubidium atom is trapped above the surface of a nanocavity in a photonic crystal waveguide. Calculations on the photonic crystal waveguide cavity resonance frequency, mode profile and quality factor are performed with the MPB (MIT photonic band) package and Meep (MIT Electromagnetic Equation Propagation) package, an FDTD simulation package. The photonic crystal will be produced using e-beam lithography and characterized in a scanning near-field optical microscope. The rubidium atoms are laser-cooled to a temperature below 50 μK. After evaporative cooling in a shallow yet tight optical dipole trap, the cloud of remaining atoms is transported to the sample by moving the focus of the optical dipole trap. When the optical power of the dipole trap is lowered, atoms can spill out of the trap and into the evanescent field of the cavity. As a result, the transmission of the cavity changes. By monitoring the transmission the dynamics of the cavity-atom system can be followed. Figure 1: (a) Illustration of the experimental setup. A rubidium atom is trapped in the evanescent field of the cavity in a photonic crystal bridge waveguide. The optical dipole trap (vertical red beam) is used to transfer atoms to the cavity. (b) Schematic representation of the atom-cavity system. The atom and the cavity are coupled by a vacuum Rabi frequency g(z) which depends on the atom-cavity separation z. The maximum vacuum Rabi frequency g ≈ 2π × 18.5 GHz. The spectral max linewidth of the cavity is γ ≈ 2π × 3.85 GHz and of the atom γ ≈ 2π × 5.89 MHz. c a [1] D. van Oosten and L. Kuipers, Phys. Rev. A 84, 011802(R) (2011).
Nanophotonics Development of intermediate reflectors for high performance tandem solar cells Dr. Oumkelthoum Mint Moustapha, O.MintMoustapha@uu.nl, phone: 030 - 253 88 56 Sponsor: EU FP7 project Helathis, since October 2011 Supervisors: Prof. dr. Ruud E.I. Schropp and dr. Jatin K. Rath VHF PECVD, Conductivity measurements, IV measurements, Raman spectroscopy Light management is a major key for the improvement of thin film solar cells. Tandem solar cell designs, which aim at absorption of a wide part of the solar spectrum, have proven their ability to improve the device efficiency [1]. As shown in Figure 1, a thin film silicon tandem structure consists of an amorphous silicon cell (top cell) connected in series to a microcrystalline silicon cell (bottom cell), respectively converting high and low energy photons to current. In order to minimize the light-induced degradation, the amorphous layer should be kept as thin as possible. Which leads to an inbalance between the currents of the top and bottom cells. In order to increase the current of the thin top cell, for proper current matching of the component cells, an intermediate reflector (IR) layer that increase the amount of the absorbed light by the top cell, can be introduced within the structure (see Figure 1). Such layer should meet the following requirements: it should reflect high photon energy light back into the top cell; transmit the light needed for the bottom cell; conduct the current between the two cells. Different approaches of IR will be investigated within this project [2]. For example: • Doped microcrystalline silicon oxide: a mixed-phase material that can combine the required optical and electrical properties depending on its depositions conditions • 1D photonic layers (distributed Bragg reflectors:DBR) based on Si and ZnO: a stack comprising alternating ZnO and Si layers can be designed to possess the desired properties. Figure 1: Schematic diagram of silicon tandem cell. [1] M.Yoshimi et al, High efficiency thin film silicon hybrid solar cell module on 1m2-class large area substrate, in: Proceedings of the Third World Conference on Photovoltaic Energy Conversion, Osaka, Japan, 2003, pp. 1566-1569. [2] Michael Vetter et al, High efficiency very large thin film silicon photovoltaic modules (HELATHIS), in: The 25th Europ. PVSEC (5th WCPEC) 6.-10. Sept. 2010, Valencia, Spain, pp. 3220 – 3223. 85
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Debye Institute for Nanomaterials S
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Introduction This book gives an ove
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Chemical Biology and Organic Chemis
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Condensed Matter and Interfaces Ani
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Self assembly of nanocrystals into
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ZnO nanowire lasers Dr. (Lam)Bert v
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Inorganic Chemistry and Catalysis I
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