Shock-produced coherent terahertz light

Physicists at MIT and Lawrence Livermore National Laboratory have uncovered a new source of coherent radiation distinct from both traditional and free-electron lasers. Their theoretical work predicts that weak but measurable coherent light in the THz regime is produced when a shock wave passes through virtually any dielectric crystal, including table salt. The light-producing mechanism is a temporally periodic polarization current produced by the concerted motion of row after row of atoms in the target crystal. The physicists were surprised by the light’s coherence, which arises not from the source of the mechanical shock but from the periodicity of the lattice. The next step will be to conduct an experimental test of the prediction at two national labs—Livermore and Los Alamos. According to team member Evan Reed, the first likely application of coherent radiation will be as a diagnostic for understanding shock waves. The radiation should also provide information about atomic-scale properties of the shocked crystal. (E. J. Reed et al., Phys. Rev. Lett. 96 , 013904, 2006 http://dx.doi.org/10.1103/PhysRevLett.96.013904 .)