arXiv subjects

Kenneth G. Libbrecht

Publications and source records attributed to Kenneth G. Libbrecht.

53 records · Page 3Linked to original sources

arXiv2009

Identification of a Novel "Fishbone" Structure in the Dendritic Growth of Columnar Ice Crystals

Ice crystals growing in highly supersaturated air at temperatures near -5 C exhibit a distinctive, nonplanar dendritic morphology that has not been previously documented or explained. We examine this structure and identify its most prominent features in relation to the ice crystal lattice. Developing a full 3D numerical model that reproduces this robust morphology will be an interesting challenge in understanding diffusion-limited crystal growth in the presence of highly anisotropic surface attachment kinetics.

cond-mat.mtrl-sci↗

arXiv2008

Measurements of Snow Crystal Growth Dynamics in a Free-fall Convection Chamber

We present a series of experiments investigating the growth of ice crystals from water vapor in the presence of a background gas. We measured growth dynamics at temperatures ranging from -2 C to -25 C, at supersaturations between 0.5 and 30 percent, and with background gases of nitrogen, argon, and air at a pressure of one bar. We compared our data with numerical models of diffusion-limited growth based on cellular automata to extract surface growth parameters at different temperatures and supersaturations. These data represent a first step toward obtaining precision ice growth measurements as a function of temperature, supersaturation, background gas pressure and gas constituents. From these investigations we hope to better understand the surface molecular dynamics that determine crystal growth rates and growth morphologies.

cond-mat.mtrl-sci↗

arXiv2008

Crystal Growth in the Presence of Surface Melting and Impurities: An Explanation of Snow Crystal Growth Morphologies

We examine the molecular dynamics of crystal growth in the presence of surface melting and surface impurities, and from this propose a detailed microscopic model for the growth of ice from the vapor phase. Our model naturally accounts for many aspects of the experimental data that are otherwise difficult to explain, and it suggests a variety of measurements that can provide further confirmation. Although additional work is needed to refine these ideas, we believe that the combined influences of surface melting and impurities provide a viable solution to the 60-year-old mystery of why snow crystal morphologies vary so dramatically with temperature.

cond-mat.mtrl-sci↗

arXiv2008

Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure

We describe observations of a novel hysteresis behavior in the growth of ice crystals under near-vacuum conditions. Above a threshold supersaturation, we find that the ice growth rate often exhibits a sudden increase that we attribute to an impurity-driven growth instability. We examine possible mechanisms for this instability, which can be used to produce clean, faceted ice surfaces.

cond-mat.mtrl-sci↗

arXiv2008

A Convection Chamber for Measuring Ice Crystal Growth Dynamics

We present the design of a general-purpose convection chamber that produces a stable environment for studying the growth of ice crystals from water vapor in the presence of a background gas. Crystals grow in free fall inside the chamber, where the temperature and supersaturation are well characterized and surprisingly uniform. As crystals fall and land on a substrate, their dimensions are measured using direct imaging and broad-band interferometry. We also present a parameterized model of the supersaturation inside the chamber that is based on differential hygrometer measurements. Using this chamber, we are able to observe the growth and morphology of ice crystals over a broad range of conditions, as a function of temperature, supersaturation, gas constituents, gas pressure, growth time, and other parameters.

cond-mat.mtrl-sci↗

arXiv2008

A Basic Thermodynamic Derivation of the Maximum Overburden Pressure Generated in Frost Heave

I describe a simple heat-engine derivation of the maximum overburden pressure that can be generated in frost heave. The method stems from the fact that useful work can, in principle, be extracted from the forces generated by an advancing solidification front via the frost heave mechanism. Using an idealized frost heave engine, together with the maximum thermodynamic efficiency of any heat engine, one can derive the maximum overburden pressure. A similar argument can also produce the maximum thermodynamic buoyancy force on a foreign object within a solid surrounded by a premelted layer.

cond-mat.mtrl-sci↗

arXiv2008

Physically Derived Rulesfor Simulating Faceted Crystal Growth using Cellular Automata

We derive a set of algorithms for simulating the diffusion-limited growth of faceted crystals using local cellular automata. This technique has been shown to work well in reproducing realistic crystal morphologies, and the present work provides a more rigorous physical foundation that connects the numerical code to the physics of attachment kinetics and diffusion dynamics. We then apply these algorithms to examine a novel morphological transition in the growth of thin plate-like crystals.

cond-mat.mtrl-sci↗

arXiv2006

Modeling Diffusion-Limited Crystal Growth from Vapor using a Commercial Finite-Element Analysis Code

This application note describes how to model diffusion-limited crystal growth from vapor using QuickField - a commercial finite-element analysis code. The crystal growth problem is cast into the format of a steady-state heat diffusion problem, which is one type of problem QuickField is designed to solve, and we derive the relevant conversion factors and correspondences between variables. We also describe three types of boundary conditions in the crystal growth problem and their corresponding boundary conditions in the heat diffusion problem. As an example, we examine the crystal growth of ice from water vapor in a background gas using a variety of mixed boundary conditions.

cond-mat.mtrl-sci↗

arXiv2006

Precision Measurements of Ice Crystal Growth Rates

I describe techniques for making precise measurements of the growth rates of the principal facets of ice crystals. Particular attention is paid to identifying and reducing systematic errors in the measurements, as these have plagued earlier attempts to determine ice growth rates. I describe the details of an experimental apparatus we are currently using, and I describe some preliminary results for growth of basal facets at T=-15 C.

cond-mat.mtrl-sci↗

arXiv2005

Direct Observation of Broadband Coating Thermal Noise in a Suspended Interferometer

We have directly observed broadband thermal noise in silica/tantala coatings in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with the prediction based on indirect, ring-down measurements of coating mechanical loss, validating that method as a tool for the development of advanced interferometric gravitational-wave detectors.

gr-qc↗

arXiv2004

A Critical Look at Ice Crystal Growth Data

I review published data relating to the growth of ice crystals from water vapor under various conditions, and I critically examine the different measurements to determine what useful information can be extracted from each. I show that most, and possibly all, of the existing growth data have been seriously distorted by systematic errors of one form or another, to varying degrees. Many data sets are dominated by systematic effects, so that the conclusions drawn from them are unreliable. I list and describe these systematic errors in some detail so that they may be avoided in future experiments. I then cautiously draw conclusions from the growth data and compare with theories pertaining to our current understanding of the crystal growth dynamics of ice.

cond-mat.mtrl-sci↗

arXiv2004

Thermoelastic-damping noise from sapphire mirrors in a fundamental-noise-limited interferometer

We report the first high-precision interferometer using large sapphire mirrors, and we present the first direct, broadband measurements of the fundamental thermal noise in these mirrors. Our results agree well with the thermoelastic-damping noise predictions of Braginsky, et al. [Phys. Lett. A 264, 1(1999)] and Cerdonio, et al.[Phys. Rev. D 63, 082003 (2001)], which have been used to predict the astrophysical reach of advanced interferometric gravitational wave detectors.

gr-qc↗

arXiv2004

Enhanced photothermal displacement spectroscopy for thin-film characterization using a Fabry-Perot resonator

We have developed a new technique for photothermal displacement spectroscopy that is potentially orders of magnitude more sensitive than conventional methods. We use a single Fabry-Perot resonator to enhance both the intensity of the pump beam and the sensitivity of the probe beam. The result is an enhancement of the response of the instrument by a factor proportional to the square of the finesse of the cavity over conventional interferometric measurements. In this paper we present a description of the technique, and we discuss how the properties of thin films can be deduced from the photothermal response. As an example of the technique, we report a measurement of the thermal properties of a multilayer dielectric mirror similar to those used in interferometric gravitational wave detectors.

cond-mat.mtrl-sci↗

arXiv2003

Toward Quantum-Limited Position Measurements Using Optically Levitated Microspheres

We describe the use of optically levitated microspheres as test masses in experiments aimed at reaching and potentially exceeding the standard quantum limit for position measurements. Optically levitated microspheres have low mass and are essentially free of suspension thermal noise, making them well suited for reaching the quantum regime. Table-top experiments using microspheres can bridge the gap between quantum-limited position measurements of single atoms and measurements with multi-kg test masses like those being used in interferometric gravitational wave detectors.

quant-ph↗

arXiv2003

On the Formation of Thin Ice Crystal Plates: A New Type of Morphological Instability in Diffusion-Limited Growth

We propose a new type of morphological instability in the diffusion-limited growth of faceted crystals from the vapor phase that can explain the formation of thin ice plates at temperatures near -15 C. The instability appears when the attachment kinetics for facet growth depends strongly on the morphology of the facet surface. In particular, we propose that the condensation coefficient for growth of ice prism facets increases dramatically when the width of the facet approaches atomic dimensions. This model reconciles several conflicting measurements of ice crystal growth, and makes additional predictions for future growth experiments. Other faceted crystalline materials may exhibit similar morphological instabilities that promote the diffusion-limited growth of thin plate-like or needle-like crystal structures.

cond-mat.mtrl-sci↗

arXiv2002

A Search for CO Absorption in the Transmission Spectrum of HD 209458b

We observed one transit of the extrasolar planet HD 209458b with the NIRSPEC spectrograph on the Keck II telescope. Using time series of low-noise observations in the wavelength range 2.0 micron to 2.5 micron, we searched for extra absorption from the 1st overtone rotation-vibration band of CO near 2.3 micron. This was not detected, with a detection limit that fails to test simple models of the planetary atmosphere by a factor of about 3. Great improvements in the detectability of the CO spectrum features could be realized by observing a transit that is centered near stellar meridian passage, and in better weather. Since it appears that similar observations taken under better circumstances might succeed, we describe our analysis procedures in detail.

astro-ph↗

arXiv2001

Electrically Enhanced Free Dendrite Growth in Polar and Non-polar Systems

We describe the electrically enhanced growth of needle crystals from the vapor phase, for which there exists a morphological instability above a threshold applied potential. Our improved theoretical treatment of this phenomenon shows that the instability is present in both polar and non-polar systems, and we provide an extension of solvability theory to include electrical effects. We present extensive experimental data for ice needle growth above the electrical threshold, where at $T=-5$C high-velocity shape-preserving growth is observed. These data indicate that the needle tip assumes an effective radius} $R^{\ast}$ which is nearly independent of both supersaturation and the applied potential. The small scale of $R^{\ast}$ and its response to chemical additives suggest that the needle growth rate is being limited primarily by structural instabilities, possibly related to surface melting. We also demonstrate experimentally that non-polar systems exhibit this same electrically induced morphological instability.

cond-mat.mtrl-sci↗