A multichannel spectrometer for correlated EPR-optical absorption analysis of photochromic processes in crystals

A fast optical fiber multichannel spectrometer that has been developed for simultaneous measurements of EPR and optical absorption of defects in crystals is described. The setup is designed for establishing correlations between both phenomena by observing their changes under varying pump light energies. In this way optical bands are assigned to the defects causing them. After this calibration step, the pump-light-induced variations of the band intensities alone serve to unravel the responsible charge transfer processes. The speed of the spectrometer 14 ms for one spectrum in the range 400 nm to 1100 nm - is the basis for such experiments. A special scheme for evaluation of the spectra allows a fast overview of the phenomena occuring on the atomic level. Examples based on two types of photochromic BaTiO3 crystals are given. The extension of this type of spectroscopy to other fields, where correlation between EPR and optical phenomena is essential, is discussed.