Search results for "Bragg's law"
showing 10 items of 21 documents
Space-borne Bose–Einstein condensation for precision interferometry
2018
Space offers virtually unlimited free-fall in gravity. Bose-Einstein condensation (BEC) enables ineffable low kinetic energies corresponding to pico- or even femtokelvins. The combination of both features makes atom interferometers with unprecedented sensitivity for inertial forces possible and opens a new era for quantum gas experiments. On January 23, 2017, we created Bose-Einstein condensates in space on the sounding rocket mission MAIUS-1 and conducted 110 experiments central to matter-wave interferometry. In particular, we have explored laser cooling and trapping in the presence of large accelerations as experienced during launch, and have studied the evolution, manipulation and interf…
Fast microscopic method for large scale determination of structure, morphology, and quality of thin colloidal crystals.
2006
We present a novel fast microscopic method to analyze the crystal structures of air-dried or suspended colloidal multilayer systems. Once typical lattice spacings of such films are in the range of visible light, characteristic Bragg scattering patterns are observed. If in microscopic observations these are excluded from image construction, a unique color coding for regions of different structures, morphologies, and layer numbers results. Incoherently scattering defect structures, however, may not be excluded from image construction and thus remain visible with high resolution.
Double Bragg Interferometry.
2015
We employ light-induced double Bragg diffraction of delta-kick collimated Bose-Einstein condensates to create three symmetric Mach-Zehnder interferometers. They rely on (i) first-order, (ii) two successive first-order, and (iii) second-order processes which demonstrate the scalability of the corresponding momentum transfer. With respect to devices based on conventional Bragg scattering, these symmetric interferometers double the scale factor and feature a better suppression of noise and systematic uncertainties intrinsic to the diffraction process. Moreover, we utilize these interferometers as tiltmeters for monitoring their inclination with respect to gravity.
<title>Forward diffracted parametric X radiation from a thick Tungsten single crystal at 855 MeV electron energy</title>
2007
Features of forward diffracted Parametric X-Radiation (PXR) were investigated at experiments with the 855 MeV electron beam of the Mainz Microtron MAMI employing a 410 micrometer thick tungsten single crystal. Virtual photons from the electron field are diffracted by the (10-1) plane at a Bragg angle of 3.977 degree. Forward emitted radiation was analyzed at an energy of 40 keV with the (111) lattice planes of a flat silicon single crystal in Bragg geometry. Clear peak structures were observed in an angular scan of the tungsten single crystal. The results were analyzed with a model which describes forward diffracted PXR under real experimental conditions. The experiments show that forward d…
Acoustically tunable photonic band gap structures
2005
We discuss the formation of a tunable one-dimensional photonic band gap structure through the modulation of the resonance frequency of an optical microcavity by a surface acoustic wave (SAW). The microcavity consists of a λ/2 GaAs layer bounded by AlAs/GaAs Bragg mirrors. The SAW periodically modulates the optical thickness of the cavity layer, leading to a light dispersion relation folded within a mini-Brillouin zone (MBZ) defined by |k x |≤ π/λ SAW (k x denotes the photon wave vector component along the SAW propagation direction x-with-caret). In reflection and diffraction experiments, we observe photon modes bounding the gaps in the center and at the boundary of the MBZ as well as a reno…
Thermodynamic and neutron diffraction studies of the nucleation of solid4He on graphite
1982
The nucleation of solid layers of4He on the surface of exfoliated graphite (Grafoil) was investigated by thermodynamic and neutron diffraction measurements. The thermodynamic measurements consisted of recording isopycnals in the vicinity of the melting curve. The isopycnals show a rounding in comparison to the bulk ones, which can be explained by a continuous solidification of4He on the surface of graphite in a layer-by-layer mode in the van der Waals field of the substrate. Moreover, we found a hysteresis behavior of the isopycnals, probably due to defect states in the solidified film. The thickness of the solid film is estimated by means of a simple solidification model. The neutron diffr…
Observation of Oriented Close-Packed Lattice Planes in Polycrystalline Hard-Sphere Solids.
1998
We report time-resolved Bragg scattering experiments on solidifying colloidal suspensions of hard spheres. The polar angle-averaged, integrated intensity of the (111) and (311) reflections show a transient, two-step behavior below melting, which depends in a complex way on the volume fraction and is not present for (200) or (220). Detailed analysis of the full two-dimensional scattering pattern reveals intensity maxima of sixfold symmetry close to the position of the (111) and (311) Debye-Scherrer rings. These can be explained assuming oriented crystals with close-packed planes parallel to the container walls. We show that the observed temporal behavior is due to competing homogeneous and h…
Opaline Hydrogels: Polycrystalline Body-Centered-Cubic Bulk Material with an in Situ Variable Lattice Constant
2007
Opaline hydrogels were produced as a polycrystalline bulk material with a body-centered-cubic (bcc) structure by immobilization of self-ordered charged colloidal particles crystallized under equilibrium conditions in a poly(acrylamide) matrix. The final size of a polycrystalline sample is about 7 cm3; a single crystal is up to several millimeters in length. The crystal size is tunable by varying the amount of photoinitiator and the hydrogel volume change due to swelling. The resulting photonic crystals are of high quality, showing high-order reflections. These hydrogels show a reversible shift of the diffraction Bragg peak wavelength depending on external conditions due to swelling or shrin…
Interface properties of magnetic tunnel junctionLa0.7Sr0.3MnO3/SrTiO3superlattices studied by standing-wave excited photoemission spectroscopy
2010
The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical and core-hole multiplet theoretical modeling. Epitaxial superlattice samples consisting of 48 and 120 bilayers of LSMO and STO, each nominally four unit cells thick, and still exhibiting LSMO ferromagnetism, were studied. By varying the incidence angle around the superlattice Bragg condition, the standing wave was moved vertically through the interfaces. By comparing experiment to x-ray optical c…
Near-field characterization of Bragg mirrors engraved in surface plasmon waveguides
2004
International audience; Surface plasmon waveguides (SPW's) are metal ridges featuring widths in the micrometer range and thicknesses of a few tens of nanometers. A focused ion beam has been used to carve microscatterers into gold SPW's and the near-field distributions around these microstructures are observed by means of photon scanning tunneling microscopy (PSTM). On the basis of near-field images, we show that a finite length periodic arrangement of narrow slits can reflect a surface plasmon mode propagating along a SPW. The reflection efficiency of the micrograting is found to depend upon the number of slits, the period of the grating, and the incident wavelength. The optimum reflection …