The elastic moduli of fused quartz have been determined by ultrasonic measurements under high hydrostatic compressive stress and showed a nonlinear decrease to a minimum value at 2.1–2.5 GPa, and thereafter an increase with increasing pressure. Changes in the Debye temperature and the Grüneisen constant are determined using the present results. Assuming a contribution of the fourth-order elastic constants to the nonlinear dependence, C1111, C1112, C1122, and C1123 have been tentatively evaluated to be 11.0±1.0, 10.8±3.6, 22.7±11.1, and 8.6±2.0 TPa, respectively. However, the possibilities of a complicated potential curve or a higher-order phase transition are also discussed.

High-power electromagnetic waves propagating in a negative-permeability space were investigated theoretically and experimentally, and they generated overdense plasmas successfully. Theoretical analysis predicted that high-density plasmas with negative permittivity can form via saddle-node bifurcations within an adequate electric field. To confirm theoretical predictions, using metamaterials with negative permeability achieved by magnetic resonances, we injected microwaves with several hundreds of watt into a waveguide filled with a low-pressure discharge gas. Langmuir probe measurement revealed that a generated plasma is well beyond the cutoff density for the wave frequency of 2.45 GHz, and indicated transition between positive-permittivity (low-electron-density) and negative-permittivity (overdense) states.

The modes of wave propagation in media with a negative dielectric constant are not simple, unlike those for electromagnetic waves in media with a positive dielectric constant (where modes propagate inside the media with positive phase velocity since the refractive index is usually positive). Instead, they depend on the permeability sign, either positive or negative, and exhibit completely different features. In this report, we investigated a wave confined on the surface of a negative-dielectric-constant and a positive-permeability plasma medium for which the refractive index is imaginary. The propagation mode is similar to surface plasmon polaritons on the metal containing free electrons, but its frequency band is different due to the significant spatial gradient of the dielectric constant and a different pressure term. We also studied a wave with a negative dielectric constant and negative permeability, where the refractive index is negative. This wave can propagate inside the media, but its phase velocity is negative. It also shares similar qualities with waves in plasmonic devices with negative permeability in the photon range.

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