The absorption coefficient of pure water was found to be 0.00017 cm−1 at 488 nm and 0.00029 cm−1 at 541.5 nm using adiabatic laser calorimetric techniques. These values are in good agreement with the generally accepted long-path transmission spectra of Clarke and James.

The infrared absorption coefficients of NaCl, KCl, NaF, CaF2 and BaF2 have been determined by calorimetric techniques at the laser wavelengths 1.06, 2.7, and 3.8 μm. The absorption level of the best crystals can be 10−5 cm−1 or lower at l.06 μm, but no crystal with a coefficient lower than 10−4 cm−1 at 2.7 and 3.8 μm has been found. Possible reasons for these results are discussed.

Potassium bromide single crystals have been prepared with 10.6-μm bulk absorption coefficients smaller than the intrinsic value for potassium chloride. Of several halogen-producing vapors studied, that of carbon tetrachloride is most effective in decreasing infrared absorption. Water-grinding, followed by polishing with HBr solutions, produces non-absorbing and etch-pit-free surfaces on planes remote from (100). Hydroxyl lines are absent from infrared absorption spectra of all crystals. Vacuum-ultraviolet absorption at 215 nm shows presence of between 0.01 and 4.0 OH− ions per million anions. Incomplete removal of metaborate (BO−2) by iodine monobromide or by hexabromobenzene is evident in infrared absorption spectra.

Laser calorimetric or thermal rise techniques are useful for the determination of very low absorption coefficients in solids. A number of improvements in this technique are described of which the most important is a means of separating surface and bulk absorption. These techniques have been applied to study alkali halides in the ir but are applicable where laser sources of sufficient power are available.

The production of smooth scratch-free surfaces on the alkali halides KCl and NaCl by means of solvent action is described. It is shown by etching studies that very few dislocations are introduced by this process. Surfaces of the type described are of particular value in the study of the optical absorption of very low loss materials.

The infrared absorption in KCl single crystals near 10.6 μm has been studied using calorimetric techniques with fixed-frequency and tunable CO2 laser sources. By use of crystals grown in a reactive CCl4 atmosphere, with surfaces carefully prepared by chemical polishing, it is possible to obtain absorption coefficients of 0.0002 cm−1 or less in samples several centimeters thick. This residual absorption is composed of a surface and a bulk part. It is possible to show that the bulk absorption approaches the estimated intrinsic limit of 0.00008 cm−1. An absorption band near 9.8 μm is present in all samples examined and appears to be largely associated with the surface.

This paper presents a study of electrical breakdown effects on LiF cleavage surfaces situated in compressed nitrogen gas. The object of interest is the (100) dendrite. As first reported by Gilman and stauff, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> this dendrite forms extensive surface patterns on the cleavage face of LiF crystals situated in dielectric liquids when subjected to dc positive (dominant pattern) and negative breakdown voltage. Its classification as a dislocation feature was not accepted by workers at NRL2 who found it to be grooved and channeled. However, since dislocation spike structures, known as screw pairs, were found about some dielectric breakdown paths, 3 the question of primacy was not resolved. According to the basic observations and ideas of von Hippel, 4 substantiated by the work of Cooper and Elliott5 and of Davisson, 6 and treated theoretically by Offenbacher and Callen, 7 the dielectric breakdown path is produced by the disruptive action of oriented electron avalanches which results initially in the formation of dislocation-free, plasma-containing, grooves and channels. The orientation is due to the Brillouin zone structure of the normal modes of lattice vibration. Gilman and stauff1 have proposed that dielectric breakdown is preceded by a discontinuous nucleation of dislocation loops.

The recently introduced acetic acid etchant is shown to be a useful tool for investigating the impurity content of individual dislocations and grain walls in NaF crystals, since the degree of their contamination can be judged by visual inspection. In pure NaF crystals individual dislocations do not contain sufficient impurity to be sensed by the etchant, but grain walls can show large variations in their impurity content which may be regulated by the character of their dislocations. To a remarkable extent the contamination in each wall is constant, not changing sensibly with change of wall direction, but showing abrupt changes upon passing through intersections. Impure NaF crystals show impurity-saturated etching at all dislocations. This suggests that the core binding states of edge and screw dislocations are equivalent. The negative etching action of this etchant is shown to be due to the presence of polyvalent metallic impurities such as calcium.

This communication introduces acetic acid as an etchant that can sense distributed impurities in sodium fluoride crystals. It can be used to directly observe impurity reactions in these crystals.

The patterns of ice filaments are found to display the structure of the internal bias fields in colemanite. These patterns are formed by external electrical fields. The two fields, external and internal, though related, do not necessarily have the same origin, since the internal field may be due to volume charges and the external field to surface charges. Some properties of the bias field in relation to crystal perfection are discussed.

A variety of fracture phenomena associated with electrical effects are considered. These include fractures produced in solids by arc and spark discharges, fracture associated with dielectric breakdown and with electrolysis, the fracture of piezoelectric ceramics with pulsed voltage, and the disruption of whiskers in intense electrical fields.

The fracture induced in dielectric materials by corona and spark discharges in gases above atmospheric pressure will be described elsewhere. 1 The following morphology was observed: 1. No fracture was observed in materials that have a low coefficient of thermal expansion such as fused quartz and vycor. Also, no fracture was observed in cleavage slices of colemanite — a material that lacks transverse cleavage planes. 2. Craze-cracking and flaking was observed in soda glass and in the crystals fluorite, sodium brornate, and sodium nitrate. 3. Cleavage crack interpénétration was observed in crystals that manifest cubic cleavage.