Ramanspektren von ultramikroskopischen Streuzentren in LiF- und NaCl-Einkristallen

Stokes-Ramanspectra of unltramicroscopic scattering centres in LiF- and NaCl single crystals excited by the focussed light of a He-Ne-gaslaser of 21.4 mW at 632.8 nm are reported here for the first time. The spectra exhibit essentially three parts: 1. a continuum and the limiting frequency of transversal optical phonons at small frequency shifts as a first order Raman effect; 2. second order Raman effect not yet measured for LiF; 3. a strong continuum at larger wavenumbers that may be attributed to three phonon processes. This latter phenomenon becomes plausible when the high field strangth of 5×10⁵ volt/m in the closest constriction of the exciting light beam and the substantial lattice deformations in the scattering centres are considered. The spectra of LiF are by far more intensive than those of NaCl.