You are invited to attend a lecture

Nano-spectroscopy in coupled atomic-photonic chip-scale systems 

By

Liron Stern

PhD student of

Professor Uriel Levy

Applied Physics Department, Hebrew University of Jerusalem

The interaction of light with atomic vapors such as rubidium is being used extensively both in research and industry in a myriad of disciplines and applications. Notable examples include the precision of atomic clocks, the incredible reduction of speed of light, the ability to control light with another source of light, and the ability to measure minute magnetic fields with magnetometers. In traditional light-vapor experiments, vapor is enclosed in glass blown cells, and irradiated by a light source in free space. Recently, we are witnessing an ongoing effort towards the miniaturization of vapor cells and the accompanied optical systems in order to enable enhanced and efficient light-matter interactions, where a prominent effort is to facilitate the interaction of guided light with vapors.

In this talk, I will present our platform of atomic cladding plasmonic and photonic wave-guides. Specifically, I will describe two different types of nano-scale light vapor spectroscopic configurations. The first consists of a solid core silicon-nitride waveguide, interacting evanescently with rubidium vapor, offering an interaction volume orders of magnitude smaller than traditional cells. I shall present linear and non-linear spectroscopy using this platform, and the different broadening mechanisms unique to this device. Furthermore, it will be shown that due to the nano-scale confinement of light, the rubidium absorption saturates at an extremely low optical power rendering this device highly appealing for non-linear applications such as all-optical switching. Experimental results utilizing resonant structures such as atomic cladding micro ring resonators will also be presented. The second platform, is the plasmonic-atomic hybrid integrated system consisting of rubidium vapor integrated on a thin layer (~50nm) of gold supporting nanoscale confined plasmon modes. Introducing plasmonics into the world of atomic physics allows confining electromagnetic radiation to the deep nanoscale and dramatic enhancement of light-matter interactions. Using this apparatus we demonstrated the resonant coupling of plasmonic and atomic systems, and tailored this coupling to drastically modify the transmission in form of Fano resonances. Furthermore, it became possible to study fundamental effects such as controlling the selection rules of atomic transitions. I shall conclude with discussing the difference prospects of such devices for applications such as frequency referencing and all optical few photon switching.

Thursday, July 7, 2016, at 15:00

Room 011, Kitot Building

You are invited to attend a lecture

by

Dor Gabay

Ph.D. candidate of

Professor Amir Boag and Dr. Amir Natan of Electrical Engineering, Physical Electronics Department

The solution of the Poisson equation describing the electrostatic potential plays an important role in first principles methods such as Density Functional Theory (DFT), time dependent DFT (TDDFT), Hartree-Fock (HF), GW, and others. In recent years this is becoming even more important as many DFT methods utilize hybrid functionals that involve the inclusion of Fock exchange or screened exchange. The Poisson equation for the electrostatic potential, , is given by , where  is the electronic density. An alternative approach to solving the Poisson Equation is to write it in its equivalent integral form, i.e. , where  is the volumetric domain of integration and  is the electrostatic Green’s function. The volumetric integral can be efficiently evaluated using the Multi-Dimensional Fast Fourier Transform (FFT) which leads to  scaling for  grid points. The FFT-based method was therefore implemented in PARSEC, a real-space first principles Density Functional Theory (DFT) package.

In developing a Poisson solver using FFT, we analyzed both existing and novel Green’s function kernels. The proposed kernels took both analytical and numerical form. The purely analytical kernels were computationally efficient, but tended to produce insufficiently accurate results. Various optimization methods were used to fine-tune the singular region of the analytically derived kernels. The numerical kernels, although more computationally expensive, could be adjusted in accuracy by considering finer integration schemes or higher orders of approximations, making them more accurate than the non-corrected analytically derived kernels.

Finally, we demonstrate how the errors associated with the solution of the electrostatic potential propagate into errors in the eigenvalues of the Density Functional Theory (DFT) calculations.

Monday, July 4th, 2016, at 17:00

Room 011, Kitot Building