Roy M. Waxler

Optical and physical parameters of Plexiglas 55 and Lexan

The following parameters have been obtained for Plexiglas 55 and Lexan: refractive index n at 486.1 nm, 589.3 nm, and 656.3 nm, the thermooptic constant dn/dT at 632.8 nm, the linear thermal expansion coefficient; the photoelastic constants q(11), q(12), p(11), and p(12); and the elastic moduli c(11), c(12), s(11), and s(12). The experimental value for the density derivative of refractive index rho(dn/drho)T deviates by only a small amount from the value calculated from the Lorentz-Lorenz equation. This is the expected result for molecular solids. The density variation with temperature is the dominant contribution to dn/dT.

Mechanisms for self-focusing in optical glasses

The relative contributions of the Kerr, electrostrictive, and thermal effects to the self-focusing thresholds of borosilicate crown glass, fused silica, and dense flint glass have been estimated from an analysis of damage-threshold data for linearly polarized and circularly polarized radiation. The measurements were made with a Nd:glass laser operating in the TEM 00 mode with a temporal pulsewidth of 25 ns. The Kerr effect appears to be the largest effect. The thermal effect is also significant. The electrostrictive effect is smallest. Reasonable values of the absorption coefficient are calculated from the thermal contribution. The results are in qualitative agreement with the work of others.

Relation between refractive index and density of glasses resulting from annealing compared with corresponding relation resulting from compression.

The change in refractive index and associated change in density of glasses on annealing has been determined by Tool, Tilton, and Saunders. The corresponding changes for the same glasses, produced by hydrostatic compression are presented here and compared with those of Tool et al. It is found that, for a given increase in density on annealing, the increase in index is greater than for the same measured increase in density on compression. The results are interpreted in terms of equations developed by Lorentz-Lorenz, Pockels, and Mueller to show, first, that in all cases, whether from annealing or compression, there is a decrease in polarizability and an increase in density (these results are in agreement with those of previous investigators) and, second, that the decrease in polarizability for a given increase in density is greater on compression than on annealing.

Dispersion of the piezobirefringence of GaAs due to strain‐dependent lattice effects

The piezobirefringence of GaAs has been measured over the wavelength range 3.5–10.6 μm. A small yet significant dispersion is found which is attributed to the strain dependence of the transverse optic phonon. The main contribution to the dispersion appears to be due to the strain‐induced anisotropy of the transverse effective charge. The data are in reasonably good agreement with the theory of Humphreys and Maradudin. The strain‐induced relative anisotropies of the transverse effective‐charge and the high‐frequency photoelastic constants k∞11−k∞12 and k∞44 have been calculated on the basis of a two‐parameter fit to the photoelastic dispersion.

Photoelastic constants of germanium

The photoelastic constants of Ge have been measured at 3.39 and at 10.6 μm. Our stress‐birefringence data join smoothly to earlier stress‐birefringence data at other wavelengths. The acousto‐optic figure of merit M2, computed from our data, agrees well with M2 determined for commercial acousto‐optic devices. However, our data disagree with some earlier measurements of M2, the elasto‐optic constants pij, and the change of refractive index with hydrostatic pressure dn/dP.

Optical Materials Characterization, Final Technical Report February 1, 1978-September 30, 1978

Data obtained as part of the Optical Materials Characterization Program are summarized in this report. Room temperature values of refractive index as a function of wavelength are presented for the following materials: commercially grown KCl, reactive atmosphere processed (RAP) KCl, KCl nominally doped with 1.5% KI, hot forged CaF2, fusion cast CaF2, CaF2 doped with Er (0.001% to 3% Er), SrF2, chemical vapor deposited (CVD) ZnSe (2 specimens), and ZnS (CVD, 2 specimens). Data for the thermo-optic constant (dn/dT) and the linear thermal expansion coefficient are given for the following materials over the temperature range -180 degrees C to 200 degrees C: Al2O3, BaF2, CaF2, CdF2, KBr, KCl, LiF, MgF2, NaCl, NaF, SrF2, ZnS (CVD), and ZnSe (CVD). The piezo-optic constants of the following materials are presented: As2S3 glass, CaF2, BaF2, Ge, KCl, fused SiO2, SrF2, a chalcogenide glass (Ge 33%, As 12%, Se 55%) and ZnSe (CVD).

Temperature dependence of Szigeti effective charge of alkali halides

Abstract The second Szigeti relation was used to obtain the temperature dependence of the Szigeti effective charge, es. The results are discussed in the framework of the deformation dipole model. Recent experimental data are used to show that the volume derivatives of es of most ionic solids are positive, thus providing evidence that the deformation dipole model is qualitatively valid.

Photoelastic constants of potassium chloride at 10.6 μm

The piezooptic constants of pure KCl and KCl doped with KI have been measured in the visible and at 10.6 microm by interferometric and polarimetric techniques. The dispersion of the elastooptic constants, computed from the piezooptic constants, differs from the dispersion calculated from a theory based on a two-oscillator model of the refractive index.

Measuring Photoelastic and Elastic Constants of Transparent Materials by Application of Static Stress

The shift of Twyman-Green and Fizeau fringes as a function of applied uniaxial and hydrostatic stress have been measured on transparent solids. These data permit us to calculate all the photo-elastic and elastic constants of a material. At the wavelength 10.6 μm, where fringe shifts are small, we have measured photo-elastic constants using a modified Twyman-Green interferometer, which is capable of detecting fringe shifts ~0.01 λ by electronic means. Data on polycrystalline ZnSe grown by chemical vapor deposition are presented.

Relative importance of electrostriction and the Kerr effect to self‐focusing in optical glasses

The damage threshold for three optical glasses was found to be higher for circularly polarized radiation than for linear polarization, using 26‐nsec pulses from a Nd:glass laser. The damage was assumed to result from self‐focusing. The fractional contribution of electrostriction to the total nonlinear index n2 is estimated to be 0.8 ± 0.2 for borosilicate crown glass, 1.15 ± 0.35 for fused silica, and 0.4 ± 0.1 for dense flint glass, assuming the Kerr effect to be the only other self‐focusing mechanism. The data are consistent with present concepts of glass structure. The high damage threshold in fused silica is attributed to its relatively small Kerr effect.