Long-range diatomic s + p potentials of heavy rare gases

We examine the long-range part of the rare-gas diatomic potentials that connect to the R{(n-1)p5ns}+R{(n-1)p5np} atomic states in the separated atom limit (n=3, 4, 5, and 6 for Ne, Ar, Kr, and Xe, respectively). We obtain our potentials by diagonalization of a Hamiltonian matrix containing the atomic energies and the electric dipole-dipole interaction, with experimentally determined parameters (atomic energies, lifetimes, transition wavelengths, and branching ratios) as input. Our numerical studies focus on Ne and Kr in this paper, but apply in principle to all other rare gases lacking hyperfine structure. These diatomic potentials are essential for applications in which homonuclear rare-gas pairs interact at large internuclear separations, greater than about 20 Bohr radii. Among such applications are the study of cold atomic collisions and photoassociative spectroscopy

A bright ultracold atoms-based electron source

An important application of pulsed electron sources is Ultrafast Electron Diffraction [1]. In this technique, used e.g. in chemistry, biology and condensed matter physics, one can observe processes that take place at the microscopic level with sub-ps resolution. To reach the holy grail of UED, single-shot diffraction images of biologically relevant molecules, electron bunches of 1pC charge, 100fs length and 10nm coherence length are required. Conventional pulsed electron sources cannot fulfil these requirements, but according to the simulations reported in [2] and [3] a new type of source can.The new source combines the use of magneto-optical atom trapping with fast high voltage technology. We start by cooling and trapping rubidium atoms, followed by ionisation just above threshold, leading to an ultracold plasma. Another possibility is to excite the atoms into a high Rydberg level, from which they spontaneously evolve into an ultracold plasma. Applying a fast high voltage pulse, electron bunches can be extracted. In an initial study [2] it has been shown that this type of source can provide a very high brightness. Depending on the initial particle distribution, the reduced brightness can be in the order of 1x109 A/(rad2m2V), which is orders of magnitude higher than established technology such as an electron photogun can provide.Here we report the first experiments toward realisation of the source. Here, a simple accelerator structure consists of four bars surrounding a MOT, on which an 800V pulsed voltage with a rise time of 1ƒÝs is applied. An MCP together with a phosphor screen and a CCD camera are used as detection system. The bunch size obtained from the phosphor screen is fitted with a Gaussian distribution, from which the electron temperature is extracted. For small extracted charges, the electron temperature is found to have an upper limit of 500K, the measurement being limited by stray magnetic fields due to the low electron energy (10eV). We have also extracted a pulsed ion beam by reversing the sign of the accelerating voltage. Since ions are heavier, they obtain higher energy and are less influenced by the magnetic fields. The temperature in this case is found to b

State-selective imaging of cold atoms

Atomic coherence phenomena are usually investigated using single beam techniques without spatial resolution. Here we demonstrate state-selective imaging of cold 85Rb atoms in a three-level ladder system, where the atomic refractive index is sensitive to the quantum coherence state of the atoms. We use a phase-sensitive diffraction contrast imaging (DCI) technique which depends on the complex refractive index of the atom cloud. A semiclassical model allows us to analytically calculate the detuning-dependent refractive index of the system. The predicted Autler-Townes splitting and our experimental measurements are in excellent agreement. DCI provided a quantitative image of the distribution of the excited-state fraction, and compared with on-resonance absorption and blue cascade fluorescence techniques, was found to be experimentally simple and robust

Performance predictions of a focused ion beam based on laser cooling

Focused ion beams are indispensable tools in the semiconductor industry because of their ability to image and modify structures at the nanometer length scale. Here we report on performance predictions of a new type of focused ion beam based on photo-ionization of a laser cooled and compressed atomic beam. Particle tracing simulations are performed to investigate the effects of disorder-induced heating after ionization in a large electric field. They lead to a constraint on this electric field strength which is used as input for an analytical model which predicts the minimum attainable spot size as a function of amongst others the flux density of the atomic beam, the temperature of this beam and the total current. At low currents (

Laser-cooled ion source

Focused Ion Beams (FIB) are widely used in the semiconductor industry for milling, sputtering and imaging applications. In particular it is used for quality control of wafers, by using a combination of a FIB and an electron microscope to make cross-sectional inspections of wafers. In addition, FIB's are used for mask repair through gas-assisted etching

Diffraction of a released bose-einstein condensate by a pulsed standing light wave

We study the diffraction of a released sodium Bose-Einstein condensate by a pulsed standing light wave. The width of the momentum distribution of the diffracted atoms exhibits strong oscillations as a function of the pulse duration, corresponding to periodic focusing and collimation of the condensate inside the standing light wave. Applications of this thick grating regime of diffraction to atom interferometry are discussed

Beam pulsing device for use in charged-particle microscopy

A charged-particle microscope comprising: - A charged-particle source, for producing a beam of charged particles that propagates along a particle-optical axis; - A sample holder, for holding and positioning a sample; - A charged-particle lens system, for directing said beam onto a sample held on the sample holder; - A detector, for detecting radiation emanating from the sample as a result of its interaction with the beam; - A beam pulsing device, for causing the beam to repeatedly switch on and off so as to produce a pulsed beam, wherein the beam pulsing device comprises a unitary resonant cavity disposed about said particle-optical axis and having an entrance aperture and an exit aperture for the beam, which resonant cavity is embodied to simultaneously produce a first oscillatory deflection of the beam at a first frequency in a first direction and a second oscillatory deflection of the beam at a second, different frequency in a second, different direction. The resonant cavity may have an elongated (e.g. rectangular or elliptical) cross-section, with a long axis parallel to said first direction and a short axis parallel to said second direction