Spatially resolved NQR.

Pure nuclear quadrupole resonance (NQR) was combined with a rotating-frame imaging technique (rho NQRI). The method is suitable for powdery or crystalline materials containing quadrupole nuclei. The spatial information is encoded in the amplitudes of the free-induction decays (FIDs) by gradients of the radio frequency amplitude of the excitation pulse. The pulse length is incremented in a series of experiments so that a pseudo-FID can be formed from the intensities of a selected NQR line. A deconvolution procedure is used for the analysis of the pseudo-FIDs. The result is a sample profile along the gradient direction. The technique is particularly suitable for the detection of the spatial distribution of physical parameters producing NQR line shifts. Examples are stress or temperature. Two-dimensional images can be produced by rotating the sample step by step. For each orientation a profile across the sample is evaluated. A backprojection reconstruction formalism then permits the rendering of two-dimensional NQR images.     

Spatially resolved solid-state MAS-NMR-spectroscopy

A comprehensive account of spatially resolved solid-state MAS NMR of ¹³C is given. A device generating field gradients rotating synchronously with the magic angle spinner is described. Spatial resolution and sensitivity are compared for phase and frequency encoding of spatial information. The suppression of spinning sidebands is demonstrated for both cases. Prior knowledge about the involved materials can be used for the reduction of data from spatially resolved spectra to map chemical structure. Indirect detection via ¹³C NMR gives access to the information about mobility from proton-wideline spectra. Two-dimensional solid-state spectroscopy with spatial resolution is demonstrated for a rotor-synchronized MAS experiment which resolves molecular order as a function of space. By comparison of different experiments the factors affecting the spatial resolution are investigated.     

Spatially resolved multidimensional cross-correlation relaxometry

Novel protocols are presented for acquiring one- and two-dimensional relaxation time spectra from selected subvolumes of a macroscopically heterogeneous sample. Although the protocols are generally applicable, special emphasis is given to their implementation on low-cost, low-field bench-top relaxometers lacking pulse shaping or pulsed gradient facilities.     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.     

Spatially resolved measurement of rock core porosity

Density weighted, centric scan, Conical SPRITE MRI techniques are applied in the current work for local porosity measurements in fluid saturated porous media. The methodology is tested on a series of sandstone core samples. These samples vary in both porosity and degree of local heterogeneity due to bedding plane structure. The MRI porosity measurement is in good agreement with traditional gravimetric measurements of porosity. Spatially resolved porosity measurements reveal significant porosity variation in some samples. This novel MRI technique should have applications to the characterization of local porosity in a wide variety of porous media.     

Spatially resolved manipulation of single electrons in quantum dots using a scanned probe

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage-independent contribution.     

Spatially resolved photoresponse measurements on pentacene thin-film transistors

A confocal setup with a spatial resolution in the submicron regime is employed for investigating the response of pentacene transistors to local illumination. The transistors show enhanced and inhomogeneous photoresponse in the proximity of the hole-injecting contact. These inhomogeneities represent contact areas of varying injection efficiency. Thus, this technique allows imaging of contact efficiencies with submicron resolution over large areas up to hundreds of microns. Drift–diffusion simulations including a photogeneration/recombination process have been performed to model the photoresponse. The simulations illustrate that the potential drop along the channel is dramatically reduced in the illuminated area due to photoconductance (i.e. photoinjection of excitons and subsequent dissociation). Also, the injection barrier for holes is reduced if the illumination is close to the hole-injecting electrode. The rapid decay of the photoresponse with increasing distance to the positively biased electrode is caused by the limited electron mean free path in our devices.     

Spatially resolved Fourier holographic light scattering angular spectroscopy

We show for what is the first time to our knowledge that digital Fourier holography can be used to record spatially resolved angular light scattering spectra from microscopically structured samples. This is achieved in one or a few digital image captures over large millimeter-scale fields of view. Such spectra are a sensitive measure of microscopic morphology, with wide applications in biological and medical imaging. We demonstrate good agreement between results of experiment and Mie theory for the angular scattering spectra of microspheres in water extracted from local regions within reconstructed 2 x 1 millimeter image sets.     

Spatially resolved dynamic eigenmode spectrum of Co rings

The spatially resolved eigenmode spectrum of micrometer-sized Co ring elements has been determined by means of combined vector network analyzer ferromagnetic resonance and time resolved magneto-optic Kerr effect measurements. Up to 5 resonant eigenmodes were observed in the frequency range from 45 MHz to 20 GHz as a function of an external magnetic bias field. A well-defined mode structure was found for the two equilibrium states (vortex and onion) which correspond to distinctive spatial modes. The effect of dynamic inter-ring coupling on the modes in the remanent states was evinced. The experimental results are found to be in good agreement with those of micromagnetic simulations. Our results demonstrate that, in analogy to the well-defined static equilibrium magnetic states of ring elements, the eigenmode spectra of this high symmetry geometry consist of a well-defined and simple mode structure.     

Spatially resolved emission in stripe geometry GaAlAs DH lasers

Double-peak spatially resolved side emission spectra are observed in GaAlAs DH lasers with proton bombarded stripe contact. Results are explained in terms of internal stress as a result of proton bombardment of the p⁺ region and absorption shift.     

Spatially resolved multidimensional NMR spectroscopy within a single scan

We have recently demonstrated that the spatial encoding of internal nuclear magnetic resonance (NMR) spin interactions can be exploited to collect multidimensional NMR spectra within a single scan. Such experiments rely on an inhomogeneous spatial excitation of the spins throughout the sample, and lead to indirect-domain peaks via a constructive interference among the spatially resolved spin-packets that are thus created. The shape of the resulting indirect-domain echo peaks approaches a Sinc function when the chemical's distribution is uniform, but will depart from this function otherwise. It is hereby shown that a Fourier analysis of either the diagonal- or the cross-peaks resolved in these single-scan two-dimensional (2D) NMR experiments can in fact provide a weighted spatial distribution of the analyte originating such peak, thus opening up the possibility of completing spatially resolved multidimensional NMR measurements within a fraction of a second. Principles of this new mode of analysis are discussed, and examples where the potential of spatially resolved ultrafast 2D NMR spectroscopy is brought to bear are presented. Potential extensions of this approach to higher dimensions are also briefly addressed.     

Spatially resolved observation of dipole-dipole interaction between Rydberg atoms

We have observed resonant energy transfer between cold Rydberg atoms in spatially separated cylinders. Resonant dipole-dipole coupling excites the 49s atoms in one cylinder to the 49p state while the 41d atoms in the second cylinder are transferred down to the 42p state. We have measured the production of the 49p state as a function of separation of the cylinders (0-80 microm) and the interaction time (0-25 micros). In addition, we measured the width of the electric field resonances. A full many-body quantum calculation reproduces the main features of the experiments.     

Spatially resolved observation of current filament dynamics in semiconductors

Two-dimensional imaging of the nucleation and the dynamics of current filaments generated in homogeneous p-doped germanium at 4.2 K during impurity impact ionization induced avalanche breakdown has been performed. The images were obtained by scanning the specimen surface with an electron beam and by recording the beam-induced current change in the voltage-biased samples. This new method is expected to identify in particular the filament configurations showing chaotic temporal resistance behavior.     

Spatially resolved spectral interferometry for determination of subsurface structure

We describe an instrument capable of obtaining two-dimensional images of subsurface structure in real time with no moving parts. The technique is based on spectral interferometry and uses an imaging spectrograph to obtain spatially resolved spectra. A test sample consisting of microscope coverslips and a Ronchi grating was measured, illustrating the system's depth resolution of 38 mum and transverse resolution of at least 12.7 mum . The technique is readily adaptable to endoscopic delivery as well as three-dimensional real-time image acquisition.     

基于数字粒子图像测速的水雾粒径测量算法及实验

针对利用传统数字粒子图像测速（DPIV）法测量水雾粒径时粒子影像拉长对测试结果的影响,提出了基于DPIV建立的改进图像法（IIM）。设计了水雾粒径测量试验系统,对细水雾进行实时测试,并对比了采用本文算法与直接等效法测试水雾粒径子半径的差异。结果表明：采用本文的IIM得到的测试结果更为准确。通过最小二乘法对粒径分布进行拟合,发现对数正态分布函数和威布尔函数都可以较好地描述粒径分布。     

Picosecond laser-induced damage morphology: Spatially resolved microscopic plasma sites

The morphology just above threshold of damage sites caused by picosecond 1.06 μm laser pulses is shown to consist of a collection of micron-sized, spatially distinct vestiges of individual plasmas. From the observed site density, the density of electrons which may initiate breakdown can be inferred. The morphology is consistent with an avalanche ionization model, but not with absorbing inclusion damage.     

Spatially resolved dynamics of localized spin-wave modes in ferromagnetic wires

We have observed localized spin-wave modes in individual thin-film ferromagnetic wires using time-resolved Kerr microscopy as a micron-scale spectroscopic probe. The localization is due to the internal field profile present when an external field is applied in the plane of the film and perpendicular to the long axis of the wire. Spatially resolved spectra demonstrate the existence of distinct modes at the edges of a rectangular wire. Spectral images clearly show the crossover of the two edge modes into a single mode in low applied fields, in agreement with the results of micromagnetic simulations.