A low power photoemission source for electrons on liquid helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1 cm^2 of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy

The analysis of quartz c-axis fabrics using a modified optical microscope

A new fully automated microfabric analyzer (MiFA) is described that can be used for the fast collection of high-resolution spatial c-axis orientation data from a set of digital polarized light images. At the onset of an analysis the user is presented with an axial-distribution diagram (AVA - 'Achsenverteilungsanalyse') of a thin section. It is then a simple matter to build-up c-axis pole figures from selected areas of interest. The c-axis inclination and colatitudes at any pixel site is immediately available to create bulk fabric diagrams or to select measurements in individual areas. The system supports both the interactive selection of c-axis measurement sites and grid array selection. A verification process allows the operator to exclude dubious measurements due to impurities, grain boundaries or bubbles. We present a comparison of bulk and individual c-axis MiFA measurements to pole figures measured with an X-ray texture goniometer and to data collected from a scanning electron microscope furnished with electron backscatter diffraction (EBSD) facility. A second sample, an experimentally deformed quartzite, illustrates that crystal orientations can be precisely linked to any location within an individual grain. © 2007 The Authors