Organic Dyes in Laser Technology

Abstract

While capable of producing high powers ruby and neodymium lasers suffer from the serious defect of fixed frequencies, apart from the high intrinsic cost of the active materials. The emission spectra of fluorescent dyes are broad, and there is a large number of dyes with fluorescence covering the optical spectrum from 340 to 1170 nm (see Fig. l). While the fluorescence efficiency of these organic compounds is very high, it was not until 1966 that Sorokin and Lankard [l] and Schafer, Schmidt and Volze [2] achieved laser action in dyes pumped by giant pulse lasers. The dye molecular energy levels are shown schematically in Figo 2. Because of very fast radiationless internal conversion within the manifold of excited singlet states, the lasing transitions occur from the bottom vibrational level of the first excited electronic singlet state to the ground state vibrational levels, and the resulting broad band emission is homogeneously broadened. The short fluorescence lifetimes, of a few nanoseconds, severely restrict the storage of energy in the active media, and to this extent, pulsed dye lasers may be regarded as operating quasi-continuously. The design of highly efficient amplifiers for pulsed systems is correspondingly more difficult, requiring very fast optical pumping or multipass arrangements.