arXiv subjects

M. E. Reeves

Publications and source records attributed to M. E. Reeves.

4 recordsLinked to original sources

arXiv2012

Near-field ablation threshold of cellular samples at mid-IR wavelengths

We report the near-field ablation of material from cellulose acetate coverslips in water and my- oblast cell samples in growth media, with a spot size as small as 1.5 μm under 3 μm wavelength radiation. The power dependence of the ablation process has been studied and comparisons have been made to models of photomechanical and plasma-induced ablation. The ablation mechanism is mainly dependent on the acoustic relaxation time and optical properties of the materials. We find that for all near-field experiments, the ablation thresholds are very high, pointing to plasma-induced ablation as the dominant mechanism.

physics.bio-ph↗

arXiv2009

Parameter-free extraction of Thin-Film Dielectric Constants from Scanning Near Field Microwave Microscope Measurements

We present a method for extracting high-spatial resolution dielectric constant data at microwave frequencies. A scanning near field microwave microscope probes a sample and acquires data in the form of the frequency and quality factor shifts of a resonant cavity coupled to the sample. The approach reported here is to calculate the electromagnetic fields by the finite element method in both static and time-dependent modes. Cavity perturbation theory connects the measured frequency shifts to changes in the computed energy stored in the electromagnetic field. In this way, the complex permittivity of the sample is found. Of particular interest are thin-film materials, for which a method is reported here to determine the dielectric constant without the need to use any fitting parameters.

cond-mat.mtrl-sci↗

arXiv2000

Simultaneously imaging of dielectric properties and topography in a PbTiO_3 crystal by near-field scanning microwave microscopy

We use a near-field scanning microwave microscope to simultaneously image the dielectric constant, loss tangent, and topography in a PbTiO_3 crystal. By this method, we study the effects of the local dielectric constant and loss tangent in the geometry of periodic domains on the measured resonant frequency, and quality factor. We also carry out theoretical calculations and the results agree well with the experimental data and reveal the anisotropic nature of dielectric constant.

cond-mat.mtrl-sci↗

arXiv1999

Pressure Dependence of the Irreversibility Line in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$:Role of Anisotropy in Flux-Line Formation

One of the important problems of high-temperature superconductivity is to understand and ultimately to control fluxoid motion. We present the results of a new technique for measuring the pressure dependence of the transition to superconductivity in a diamond anvil cell. By measuring the third harmonic of the {\it ac} susceptibility, we determine the onset of irreversible flux motion. This enables us to study the effects of pressure on flux motion. The application of pressure changes interplanar spacing, and hence the interplanar coupling, without significantly disturbing the intraplanar superconductivity. Thus we are able to separate the effects of coupling from other properties that might affect the flux motion. Our results directly show the relationship between lattice spacing, effective- mass anisotropy, and the irreversibility line in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$. Our results also demonstrate that an application of 2.5 GPa pressure causes a dramatic increase in interplanar coupling.

cond-mat.supr-con↗