Laszlo Ujj

Distribution of Non-uniform Demagnetization Fields in Paramagnetic Bulk Solids

A general calculation for the distribution of non-uniform demagnetization fields in paramagnetic bulk solids is described and the fields for various sample geometries are calculated. Cones, ellipsoids, paraboloids, and hyperboloids with similar sample aspect ratios are considered. Significant differences in their demagnetization fields are observed. The calculation shows that the demagnetization field magnitudes decrease along the axis of symmetry (along z) where an externally applied magnetic field is aligned, and increase in the vicinity of the lateral surfaces with the largest field values found in the cone and the narrowest field distributions found in the hyperboloid. An application is made to the theoretical modeling of the 1H-NMR spectra of a single crystal of field-induced superconductor λ-(BETS)2 FeCl4 with a rectangular sample geometry, providing a good fit to the measured NMR spectra.

Contribution to the development of low frequency terahertz coherent Raman micro-spectroscopy and microscopy

We report the construction and characterization of a coherent Raman tabletop system utilizing a novel astigmatic optical focusing geometry, a broadband nanosecond optical parametric oscillator and volumetric Bragg filters assisting 3CBCRS measuring system for the first time. In order to illustrate the versatility of the measurements and reveal the molecular information obtainable, two well-characterized chemicals were selected. Polarization sensitive epi-detected 3CBCRS spectra of liquid CCl4 and calcite crystal were recorded and analyzed. An unexpected polarization dependence of the signals of the lowest frequency modes of CCl4 was observed. The 1122 third order susceptibility component was phase flipped. The non-resonant susceptibility normalized 1122 component was found to be larger than the 1111 component for the lowest vibrational modes. This anomalous comportment was attributable to the anisotropy Raman tensor invariant in the third order nonlinear susceptibility tensor.

Polarization Sensitive CARS Investigations of Controlled Molecular Rotations

The emerging field of nanotechnology requires new methodologies to be developed in order to address the needs of fabrication, manipulation, control, and measurement of motions of molecules and devices on the nanoscale. Optical excitation and control of translational, vibrational, and rotational motions can offer a unique way to achieve the desired goals by using a sequence of short laser pulses, e.g., tuned to initiate certain nuclear motions of well studied photo active proteins (e.g. PYP or Rhodopsin) or engineered larger molecular structures. Measuring nuclear motions requires structurally sensitive spectroscopy methods, and therefore spontaneous Raman and coherent Raman spectroscopies can be applied to qualitatively test and quantitatively measure such motions.Polarization Sensitive Resonance Coherent anti‐Stokes Raman Spectroscopy (PSCARS), steady state or time‐resolved, can measure controlled dipole moment reorientation through the anisotropic third order nonlinear optical susceptibility. The measur...