Accelerating reference frame for electromagnetic waves in a rapidly growing plasma: Unruh-Davies-Fulling-DeWitt radiation and the nonadiabatic Casimir effect

Shortly after Hawking's prediction of thermal radiation from black holes, it became apparent that observers in accelerating frames should see a Planck distribution of electromagnetic radiation (Unruh radiation). Since an acceleration g=980 cm/${\mathrm{sec}}^{2}$ produces a radiation temperature of only \ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ K, the detection of such thermal radiation is a major challenge. A nonlinear optical medium whose index of refraction is changing rapidly with time accelerates zero-point quantum fluctuations. The sudden ionization of a gas or a semiconductor crystal to generate a plasma on a subpicosecond time scale can produce a reference frame accelerating at \ensuremath{\sim}${10}^{20}$g relative to an inertial frame.