Experimenting from a distance in case of diffraction and interference

Diffraction and interference are basic phenomena of waves. They are treated in wave optics extensively, because experimental setups are easy to built, diffraction patterns are visible and because of their importance for further subjects at school and university (diffraction of X-rays, cristallography, Fourier-Transformation, . . . ). Unfortunately, in many cases the experiments are demonstration experiments with a few diffracting objects and not enough possibilities for the students to participate. Therefore we developed a very flexible Remotely Controlled Laboratory (RCL) about diffraction and interference—a real experiment, which can be performed over the internet. The user can choose from among 5 different wavelengths, about 150 diffracting objects and 3 different techniques of qualitative and quantitative measurement. In this contribution we describe the experimental setup, give an overview about experimental results and end with the added value of the experiment

Fourier transform infrared studies of the N₂–O₂ binary system

Solid solutions (N₂)x(O₂)₁₋x have been investigated by infrared absorption measurements mainly in the O₂ and N₂ stretching regions, between 60–10 K, completing former similar studies by Raman scattering. We produced thermodynamically stable samples by a careful thermal treatment, followed by cooling/heating cycles over weeks, during which we took spectra. From fingerprints in infrared spectra we deduce phase transition lines, solubility lines and suggest a refined, improved T–x% phase diagram with respect to inconsistencies between those in literature. Spectra of N₂–O₂ mixtures are pretty complex but referring to known spectra of pure systems N₂ or O₂ we were able to assign and interpret broad (~100 cm⁻¹) phonon side bands to fundamentals and electronic transition (O₂) depending on actual temperature and concentration. Narrow features in spectra (<10 cm⁻¹) were attributed to the vibron DOS of N₂ or O₂, whose bandwidth, band shape and intensity are different and characteristic for each phase. Differences between pure and mixed systems were pointed out. Matrix isolation technique (2 ppm of CO) was used to probe our mixture

Crystal structure of solid Oxygen at high pressure and low temperature

Results of X-ray diffraction experiments on solid oxygen at low temperature and at pressures up to 10 GPa are presented.A careful sample preparation and annealing around 240 K allowed to obtain very good diffraction patterns in the orthorhombic delta-phase. This phase is stable at low temperature, in contrast to some recent data [Y. Akahama et al., Phys. Rev. B64, 054105 (2001)], and transforms with decreasing pressure into a monoclinic phase, which is identified as the low pressure alpha-phase. The discontinuous change of the lattice parameters, and the observed metastability of the alpha-phase increasing pressure suggest that the transition is of the first order.Comment: 4 pages with three figure

From optical spectra to phase diagrams — the binary mixture N2–CO

We investigated the T–c% phase diagram of the binary system N2–CO. From changes in IR spectra of all kinds of mode excitations (phonons, vibrons) we were able to determine the temperature of phase transitions (solid–solid, solid–liquid). The improvements in comparison to structural investigations by x-rays or electrons are the following: sample growing and handling with perfect optical and thermodynamic quality; determination of actual concentration (N2)x(CO)y from optical spectra; reduction of thermal hysteresis by careful cooling–heating cycles of the samples

Site-selected luminescence of atomic europium in the solid rare gases

Site-selective excitation has been used to simplify complex emission recorded in the visible spectral region for atomic europium isolated in the solid rare gases. In addition to y8P resonance fluorescence, excitation of the y8P state produces emission from the z6P state and the metastable a10D state. Very weak emission at 690 nm is tentatively assigned to the J = 9/2 level of the z10P state. Eu atoms isolated in the red and blue sites exhibit very different temperature dependence both spectrally and temporally. For the y8P state emission the red site atoms exhibit small Stokes shifts and yield radiative lifetimes while the emission from the blue site loses intensity and the temporal profiles shorten dramatically between 10 and 16 K indicating very efficient non-radiative relaxation in this site. An analysis of the Stokes shifts exhibited for the y8P state in each site supports the attributions made in a previous publication [O. Byrne and J.G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)]10.1063/1.3564947 that the smaller blue tetravacancy site has a greater repulsive interaction with the guest. With the exception of the y8P state resonance fluorescence, the recorded decay profiles of all the other emissions exhibit multiple components. This behaviour has been attributed to the existence of multiple crystal field levels arising from the splitting of the distinct spin-orbit levels from which emission occurs