Thermalisation of a two-dimensional photonic gas in a 'white-wall' photon box

Bose-Einstein condensation, the macroscopic accumulation of bosonic particles in the energetic ground state below a critical temperature, has been demonstrated in several physical systems. The perhaps best known example of a bosonic gas, blackbody radiation, however exhibits no Bose-Einstein condensation at low temperatures. Instead of collectively occupying the lowest energy mode, the photons disappear in the cavity walls when the temperature is lowered - corresponding to a vanishing chemical potential. Here we report on evidence for a thermalised two-dimensional photon gas with freely adjustable chemical potential. Our experiment is based on a dye filled optical microresonator, acting as a 'white-wall' box for photons. Thermalisation is achieved in a photon number-conserving way by photon scattering off the dye-molecules, and the cavity mirrors both provide an effective photon mass and a confining potential - key prerequisites for the Bose-Einstein condensation of photons. As a striking example for the unusual system properties, we demonstrate a yet unobserved light concentration effect into the centre of the confining potential, an effect with prospects for increasing the efficiency of diffuse solar light collection.Comment: 15 pages, 3 figure

Jacqueline M. C. Thomas, Le parler ngbaka de Bokanga

Bouquiaux Luc. Jacqueline M. C. Thomas, Le parler ngbaka de Bokanga. In: L'Homme, 1965, tome 5 n°2. pp. 148-150

Frequency-Effects in Capacitively Coupled Radiofrequency Glow-Discharges - a Comparison between Experiments and a 2-Dimensional Fluid Model

The results of a two-dimensional fluid model for argon rf discharges in a closed cylindrical vacuum chamber are compared with experimental data from an amorphous silicon deposition reactor. Good agreement is obtained for the relation between the dc autobias voltage and the dissipated power in the frequency range 50-100 MHz at pressures between 12 and 90 Pa. A scaling law is presented for the relation between the power, the dc bias voltage, the rf excitation frequency, and the background pressure. The model yields a linear relation between the applied rf voltage and the dc bias voltage. This relation depends only on the geometry of the discharge chamber and shows an offset

On the transmission function of an ion-energy and mass spectrometer

The operation of a mass spectrometer system with an electrostatic energy analyser, designed for measurements of mass-resolved ion-energy distributions, is discussed. We show how the electric fields in the different electrostatic lenses present in the system can be optimized. These lenses direct the ions entering the system into the energy filter and the quadrupole mass filter. These lenses can exhibit chromatic aberration. The conditions without chromatic aberration have been found by simulating the ion trajectories in the part of the system up to the energy filter. Also, an experimental method is presented to find these settings. We show that the energy-dependent transmission of ions through the system is mainly determined by its acceptance angle. Ion-energy spectra from an argon plasma have been measured and corrected for the transmission of the ions through the system. Published by Elsevier Science B.V

A self-consistent fluid model for radio-frequency discharges in SiH4-H-2 compared to experiments

A one-dimensional fluid model for radio-frequency glow discharges is presented which describes silane/hydrogen discharges that are used for the deposition of amorphous silicon (a-Si:H). The model is used to investigate the relation between the external settings (such as pressure, gas inlet, applied power, and frequency) and the resulting composition of the gas and the deposition rate. In the model, discharge quantities such as the electric field, densities, and fluxes of the panicles are calculated self-consistently. Look-up tables of the rates of the electron impact collisions as a function of the average electron energy are obtained by solving the Boltzmann equation in a two term approximation for a sequence of values of the reduced electric field. These tables are updated as the composition of the background neutral gas evolves under the In fluence of chemical reactions and pumping, Pumping configuration and gas inlet are taken into account by adding source terms in the density balance equations, The effect of pumping is represented by an average residence time. The gas inlet is represented by uniformly distributed particle sources. Also the radial transport of neutrals from the discharge volume into the discharge-free volume is important. As the fluid model is one dimensional, this radial transport is taken into account by an additional source term in the density balance equations. Plasma-wall interaction of the radicals (i.e., the growth of a-Si:H) is included through the use of sticking coefficients, A sensitivity study has been used to find a minimum see of different particles and reactions needed to describe the discharge adequately and to reduce the computational effort. This study has also been used to identify the most important plasma-chemical processes and resulted in a minimum set of 24 species, 15 electron-neutral reactions, and 22 chemical reactions. Tn order to verify the model, including the chemistry used, the results are compared with data from experiments. The partial pressures of silane, hydrogen, disilane, and the growth rate of amorphous silicon are compared for various combinations of the operating pressure (10-50 Pa), the power (2.5-10 W), and the frequency (13.56-65 MHz). The model shows good agreement with the experimental data in the dust free alpha regime. Discharges in the gamma\u27 regime, where dust has a significant influence, could not be used to validate the model. (C) 1997 American Institute of Physics

Frequency-Effects in Capacitively Coupled Radiofrequency Glow-Discharges - a Comparison between a 2-D Fluid Model and Experiments

The results of a 2-D fluid model for argon radiofrequency (RF) discharges in a closed cylindrical vacuum chamber are compared with experimental data from an amorphous silicon deposition reactor operated in argon. Good agreement is obtained for the relation between the DC autobias voltage and the dissipated power in the frequency range 40-100 MHz at pressures between 10 and 60 Pa. Scaling laws are presented for the dissipated power and for the ion fluxes toward the electrodes. These quantities are expressed in the DC bias voltage, the RF excitation frequency and the background pressure, Also the uniformity of the ion fluxes is studied. The model yields a linear relation between the applied RF voltage and the DC bias voltage. This relation depends only on the geometry of the discharge chamber and shows an offset