Kossel lines in extremely asymmetric diffraction schemes

It is demonstrated theoretically that the intensity distribution within the Kossel lines in an extremely asymmetric X-ray diffraction scheme has an anomalous shape of a sharp peak exceeding the background intensity by several hundred times. The possibility of experimental observation of this phenomenon is discussed.     

Kossel lines as a new type of X-ray source

The radiation intensity distribution within the Kossel line corresponding to the extremely asymmetric pattern of X-ray diffraction has an anomalous form of a clearly manifested peak exceeding the background intensity by more than two orders of magnitude. A detailed theoretical analysis of this effect is carried out and versions of experimental observation of anomalous Kossel lines are proposed. The possibility of the employment of the effect for obtaining a new source of X rays with a narrow angular collimation is discussed.     

Direct observation of optical precursors in a region of anomalous dispersion

We create optical precursors by propagating a step-modulated optical pulse through a linear resonant dielectric absorber. The field emerging from the dielectric consists of a several-nanosecond-long spike with near 100% transmission, which decays to a constant value expected from Beer's law. This high-transmission spike might be useful for imaging applications requiring penetrating optical radiation. We compare our observations to two different theories, revealing that the spike consists of both the Sommerfeld and Brillouin precursors.     

Observation of Kossel and Kikuchi lines in thermal neutron incoherent scattering

In this Letter we report the observation of K lines (representing collectively, Kossel and Kikuchi lines) produced by monochromatic thermal neutrons interacting with a KDP (potassium dihydrogen phosphate) single crystal. Since K lines contain phase information, these observations establish the experimental basis for direct crystallographic phasing of atomic structures containing incoherent scatterers, such as hydrogen, via thermal neutron "inside source" holography.     

Kossel lines in angular distribution of X-rays excited by protons in pyrolytic graphite quasi-crystal

Kossel line profiles were experimentally studied upon 1.5-MeV proton excitation of characteristic K _α radiation of argon atoms implanted into an UPV-1T graphite quasi-crystal. It was found that Kossel line profiles depend on argon ion implantation conditions, i.e., the lines generated in crystals implanted at temperatures of 150 and 200°C exhibit different widths and contrasts. In addition to the main Kossel cone line, a second cone line was detected caused by an additional texture component in the UPV-1T pyrolytic graphite quasi-crystal.     

Single-molecule observation of anomalous electrohydrodynamic orientation of microtubules

We use fluorescence microscopy to measure the orientation and shape of microtubules-which serve as a model system for semiflexible rods-that are electrophoretically driven. Surprisingly, a bimodal orientation distribution is observed, with microtubules in either parallel or perpendicular orientations to the electric field. The occupancy of these states varies nonmonotonically with the microtubule length L and the electric field E. We also observe a surprising bending deformation of microtubules. Interestingly, all data collapse onto a universal scaling curve when the average alignment is plotted as a function of B proportional, variantEL3, which reflects the ratio between the driving force and a restoring elastic force. Our results have important implications for the interpretation of electrical birefringence experiments and, more generally, for a better understanding of the electrokinetics of rods.     

Direct observation of Josephson capacitance

The effective capacitance has been measured in the split Cooper-pair box (CPB) over its phase-gate bias plane. Our low-frequency reactive measurement scheme allows us to probe purely the capacitive susceptibility due to the CPB band structure. The data are quantitatively explained using parameters determined independently by spectroscopic means. In addition, we show in practice that the method offers an efficient way to do nondemolition readout of the CPB quantum state.     

Experimental observation on anomalous emission in Mg vapor

When the 3s3p ¹P level of an Mg atom is resonantly excited by a laser, an anomalous emission with a wavelength of 5184 Å can be observed, which corresponds to the transition for 3s4s ³S to 3s3p ³P₂. According to the temporal behavior of this emission and its intensity dependence on atom density, it is believed that the experiment seems to show the transition from a spontaneous process to a cooperative process. The population inversion between 3s4s ³S and 3s3p ³P₂ is created by inelastic collisions of the lower excited 3s3p ¹P atoms.     

Experimental observation of anomalous high harmonics at low intensities

A variety of complex phenomena occurs when an ultra-short laser pulse interacts with atoms in the 10¹³ W/cm² range: non-sequential ionisation, electron recollision, and Freeman resonances. We show that high-harmonic spectra obtained experimentally in this parameter range also display anomalous features, which are difficult to understand in the framework of the three-step, semiclassical model. The results of a systematic study of these high harmonics generated in argon, xenon, and krypton are presented. From the experimental curves, complex high-order harmonic generation phenomena are discussed. PACS 42.65.Ky; 32.80.Rm     

Spectroscopic observation of lead autoionized lines

The method of measure of local thermodynamic properties of autoionizing levels is exposed. Reabsorption of light is considered and the results of preliminary calculations for the corresponding correction are given.     

Direct observation of macroscopic charge quantization

The circuit formed by a nanoscale tunnel junction in series with a capacitance and a voltage source is the building block of most multi-junction circuits of single electronics. The state of this single electron box is entirely determined by the numbern of extra electrons on the intermediate island electrode between the junction and the capacitance. We have fabricated such a system and measured the charge on the junction capacitance, which is directly related to the average value ofn, as a function of the bias voltage using a Fulton-Dolan electrometer. At low temperature, the junction charge followed thee-periodic sawtooth function expected from the theory of macroscopic charge quantization. Strikingly,e-periodic variations were also observed when the box was superconducting. The thermal rounding of the sawtooth function is well explained by a simple model, except at the lowest temperatures.     

Direct observation of the Aharonov-Casher phase

Ring structures fabricated from HgTe/HgCdTe quantum wells have been used to study Aharonov-Bohm type conductance oscillations as a function of Rashba spin-orbit splitting strength. We observe nonmonotonic phase changes indicating that an additional phase factor modifies the electron wave function. We associate these observations with the Aharonov-Casher effect. This is confirmed by comparison with numerical calculations of the magnetoconductance for a multichannel ring structure within the Landauer-Büttiker formalism.     

Direct observation of the transversal Doppler-shift

An experiment is reported in which the second order Doppler-shift has been determined by the observation of theHα-line emitted by linearly moving hydrogen atoms of velocities 2.53×10⁸ cm/s?9.28×10⁸ cm/s. In contrast to previous experiments the direct transversal observation has been used for the first time. The coefficient of the second order term in the relativistic approximation is found to be 0.52±0.03 which compares good with the theoretical value of 1/2.     

Direct observation of double diffraction patterns

The double diffraction light intensity of two identical gratings placed parallel in the Fresnel region is sensitive to the lateral displacement ΔX, and is also affected by the air gap R between the gratings. In this note, the dependence of the double diffraction light intensity on ΔX and R for each order beam has been obtained directly by observing the intensity pattern on a screen.     

Direct observation of polariton velocity in CuCl

Dynamic behaviour of the polariton-polariton resonant scattering process in CuCl was observed in a forward scattering configuration using a picosecond tunable source. The propagation times of the polariton in the crystal was estimated at various energies near the transverse exciton. They are well fitted with the theoretical group velocity calculated from the dispersion curve of the polariton.