Automated c-axis analyzers are a critical tool for harvesting large-scale ice crystal orientation data from thin section analysis, but existing examples are not designed for deployment into the field. We demonstrate a possible solution to this need with the Automated Lightweight Portable Analyzer for C-Axes (ALPACA), which implements the established four-sequence measurement algorithm of Wilen (2000) using three motorized axes of motion in a unit with volume about 0.034 cubic meters. In tests of eight easily-visible grains in thin section WDC-06A 420 VTS, ALPACA’s polarizer rotation angles of extinction agreed with previously published data to within 5º on all but one sequence of a single grain, with average sequence errors of 1.6º, 1.3º, 1.4º, and 2.9º. The information produced by these automated measurements enable production of complete grain-by-grain orientation data.

A new instrument for high-resolution optical logging has been built and tested in Antarctica. Its purpose is to obtain records of volcanic products and other scattering features, such as bubbles and impurities, preserved in polar ice sheets, and it achieves this by using long wavelength near-infrared light that is absorbed by the ice before many scattering events occur. Longer wavelengths ensure that the return signal is composed primarily of a single or few backscattering event(s) that limit its spatial spread. The compact optical logger features no components on its body that draw power, which minimizes its size and weight. A prototype of the logger was built and tested at Siple Dome A borehole, and the results were correlated with prior optical logging profiles and records of volcanic products from collected ice core samples.

Abstract A method has been devised and tested for measuring the c-axis orientation of crystal grains in thin sections of glacier ice. The crystal orientation and grain size of ice are of great interest to glaciologists since these parameters contain information on the prior thermal and flow history of the ice. The traditional method of determining c-axis orientation involves a transmission measurement through an ice sample, a process that is time-consuming and therefore impractical for obtaining a continuous record. A reflection- or backscatter-based method could potentially be used inside boreholes, with bubbles as reflectors to avoid such drawbacks. The concept demonstration of this paper is performed on ice slices, enabling a direct comparison of accuracy with traditional methods. Measurements of the crystal orientations (θ, ϕ) in 11 grains showed an average error of ±0.8° in ϕ, with no grain error >1.4°. Measurements of θ showed an average error of ±8.2° on ten grains, with unexplained disagreement on the remaining grain. Although the technique is applied specifically to glacier ice, it should be generally applicable to any transparent birefringent polycrystalline material.

Vertical electrostatic wedge actuators are described that control nanometer-scale gaps between surfaces. Standard parallel-plate electrostatic actuators become difficult to stabilize across extremely small gaps because the nature of the forces and the force laws that describe them often deviate from a Coulomb's law dependence. In this work, a nanometer-scale air gap between a collapsed cantilever structure formed by two facing In0.53Ga0.47As surfaces, with areas of tens of microns, was controlled by a wedge electrostatic actuator. Upon actuation, the gap spacing between the surfaces was tuned over a maximum range of 55 nm with an applied voltage of 60 V.

An actuator was designed and fabricated to actively tune the nanometer-scaled gap between quantum wells in a collapsed cantilever structure. Maximum actuation of 55nm was achieved. Photoluminescence from the quantum wells at the collapsed cantilever was observed at cryogenic temperature, indicating that the wells remained intact after fabrication.

A nanomechanical actuator was fabricated to control the electron states of quantum wells coupled across air gaps. This actuator was composed of a collapsed cantilever containing quantum wells and a set of parallel plate electrostatic actuators. The actuators were designed to alter the coupling distance between the wells by a few nanometers over a 200nm gap. The actuation region is separated from the quantum coupling regions so that Stark effect interference is avoided. Preliminary raw data suggests actuator motion. Such an actuator may be applied to infrared photodetectors with wide tuning ranges.

Mechanical position is used to control the wavelength of light emission of semiconductor heterostructures. The heterostructures are coupled across a gap that varies with position to tune electron states in much the same manner that optical cavities can be coupled across a tunable reflectivity mirror to control photon states. In the experiments, a SixN/InP cantilever containing an InGaAs surface well collapses over another InGaAs quantum well. The spacing between the wells varies along the cantilever, such that the heterostructure band gap is determined by the mechanical bending of the cantilever. Photoluminescence measurements of the coupled 200°A surface wells show a wavelength shift of up to 22 nm. Associated theory shows that mechanical quantum coupling enables interband or intersubband devices with unprecedented spectral tuning ranges for gain or absorption.

Strong correlations have been found in the polarization of light transmitted through a polycrystalline material and the grain sizes and orientations of that material. Experiments and supporting simulations with irregularly shaped single quartz crystals show that linear polarization is lost more rapidly as grain sizes decrease and the angular spread of the crystal orientations increase. A quantitative method using Stokes matrices to predict such changes is described and experimentally verified using an apparatus to vary the orientation of irregular quartz crystals. Grain sizes are varied between 1mm and 4mm, and the angular spreads in the crystal orientation are varied between 9 degrees and 27 degrees . This technique has applications to identify changes in crystal structure of transparent uniaxial polycrystalline materials, especially in the nondestructive characterization of glacial ice.

Mechanical positioning is used to control the wavelength of light emission from semiconductor heterostructures. In our work, a SixN/InP cantilever containing an InGaAs surface well collapses over another InGaAs quantum well. The spacing between the wells varies along the collapsed cantilever, changing the coupling between heterostructures and thus the electron states. In an essence, we are altering the bandgap by the mechanical bending of the cantilever. This is very much similar to the control of photon states by coupling optical cavities with tunable mirrors. Here we report a wavelength shift of up to 22 nm in photoluminescence measurements of two coupled 200 Å surface wells. Associated theory shows that mechanical quantum coupling enables interband or intersubband devices with unprecedented spectral tuning ranges for gain or absorption.

Optical coating degradation under laser irradiation can take several forms. Perhaps the most common that is not due to particulates is thermal breakdown, caused by heating of the coating to a catastrophic failure induced by local melting, delamination, evaporation, or some other change. We demonstrate that micromachined dielectric membranes show strong differences in their hydroxyl signatures as measured by Fourier-transform IR spectroscopy. The changes correspond to regions of high fluence (3200 J/cm2) from a Nd:YAG laser. It is found that the absorption peaks associated with OH decrease after laser treatment, indicating a reduction in the number of film hydroxyl groups.

Two surface quantum wells in a collapsed heterostructure couple across an air gap of variable width. Experiments demonstrate a tuning range of 22 nm with the potential for up to 225 nm.

Laser induced damage can take several forms. Perhaps the most common is thermal breakdown, caused by heating of the coating to a catastrophic failure induced by local melting, delamination, evaporation, or some other change. We demonstrate that micromachined dielectric membranes show strong differences in their hydroxyl signatures as measured by Fourier transform infrared spectroscopy. The changes correspond to regions of high fluence (3200 J/cm2) from a Nd:YAG laser. It is found that the absorption peaks associated with O-H stretching mode decrease after laser treatment, indicating a reduction in the number of film hydroxyl groups.