a b s t r a c tWe present a computer program and underlying model to calculate the electric susceptibility of a gas, which is essential to predict its absorptive and dispersive properties. Our program focuses on alkali-metal vapours where we use a matrix representation of the atomic Hamiltonian in the completely uncoupled basis in order to calculate transition frequencies and strengths. The program calculates various spectra for a weak-probe laser beam in an atomic medium with an applied axial magnetic field. This allows many optical devices to be designed, such as Faraday rotators/filters, optical isolators and circular polarisation filters. Fitting routines are also provided with the program which allows the user to perform optical metrology by fitting to experimental data. Program summary Program title: ElecSus Catalogue identifier: AEVD_v1_0Program summary URL:

Small numbers of surface-bound molecules are shown to behave as would be expected for optomechanical oscillators placed inside plasmonic nanocavities that support extreme confinement of optical fields. Pulsed Raman scattering reveals superlinear Stokes emission above a threshold, arising from the stimulated vibrational pumping of molecular bonds under pulsed excitation shorter than the phonon decay time, and agreeing with pulsed optomechanical quantum theory. Reaching the parametric instability (equivalent to a phonon laser or "phaser" regime) is, however, hindered by the motion of gold atoms and molecular reconfiguration at phonon occupations approaching unity. We show how this irreversible bond breaking can ultimately limit the exploitation of molecules as quantum-mechanical oscillators, but accesses optically driven chemistry.

Here we report on measurements of the absolute absorption spectra of dense rubidium vapour on the D1 line in the weak-probe regime for temperatures up to 170• C and number densities up to 3 × 10 14 cm −3 . In such vapours, modifications to the homogeneous linewidth of optical transitions arise due to dipole-dipole interactions between identical atoms, in superpositions of the ground and excited states. Absolute absorption spectra were recorded with deviation of 0.1% between experiment and a theory incorporating resonant dipole-dipole interactions. The manifestation of dipole-dipole interactions is a self-broadening contribution to the homogeneous linewidth, which grows linearly with number density of atoms. Analysis of the absolute absorption spectra allow us to ascertain the value of the self-broadening coefficient for the rubidium D1 line: β/2π = (0.69 ± 0.04) × 10 −7 Hz cm 3 , in excellent agreement with the theoretical prediction.

A light, compact optical isolator using an atomic vapor in the hyperfine Paschen-Back regime is presented. Absolute transmission spectra for experiment and theory through an isotopically pure 87 Rb vapor cell show excellent agreement for fields of 0.6 T. We show π/4 rotation for a linearly polarized beam in the vicinity of the D 2 line and achieve an isolation of 30 dB with a transmission > 95 %.

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We fabricate hetero-component 'dimers' built from a single 40 nm gold and a single 40 nm silver nanoparticle separated by sub-5 nm gaps. Successful assembly mediated by a specialized DNA origami platform is verified by scanning electron microscopy and energy-dispersive X-ray characterization. Dark-field optical scattering on individual dimers is consistent with computational simulations. Direct plasmonic coupling between each nanoparticle is observed in both experiment and theory only for these small gap sizes, as it requires the silver dipolar mode energy to drop below the energy of the gold interband transitions. A new interparticle-spacing-dependent coupling model for heterodimers is thus required. Such Janus-like nanoparticle constructs available from DNA-mediated assembly provide an effective tool for controlling symmetry breaking in collective plasmon modes.

We investigate experimentally and theoretically the Faraday effect in an atomic medium in the hyperfine Paschen-Back regime, where the Zeeman interaction is larger than the hyperfine splitting. We use a small permanent magnet and a micro-fabricated vapour cell, giving magnetic fields of the order of a tesla. We show that for low absorption and small rotation angles, the refractive index is well approximated by the Faraday rotation signal, giving a simple way to measure the atomic refractive index. Fitting to the atomic spectra, we achieve magnetic field sensitivity at the 10 −4 level. Finally we note that the Faraday signal shows zero crossings which can be used as temperature insensitive error signals for laser frequency stabilization at large detuning. The theoretical sensitivity for 87 Rb is found to be ∼ 40 kHz • C −1 .

Here we report on measurements of the absolute absorption and dispersion properties of an isotopically pure 87 Rb vapour for magnetic fields up to and including 0.6 T. We discuss the various regimes that arise when the hyperfine and Zeeman interactions have different magnitudes, and show that we enter the hyperfine Paschen-Back regime for fields greater than 0.33 T on the Rb D 2 line. The experiment uses a compact 1 mm 3 microfabricated vapour cell that makes it easy to maintain a uniform and large magnetic field with a small and inexpensive magnet. We find excellent agreement between the experimental results and numerical calculations of the weak probe susceptibility where the line positions and strengths are calculated by matrix diagonalization.