GB1348647A - Lasers - Google Patents

Abstract

1348647 Luminescent materials and uses thereof WESTERN ELECTRIC CO Inc 14 May 1971 [15 May 1970] 14949/71 Heading C4S [Also in Division H1] A dye-laser active medium comprises an exciplex, that is an excited complex formed by a reaction between two compounds, one of which is in an excited state. The compounds are chosen so that the peak of the emission spectrum of the exciplex is at least 500 Š away from the peak emission of the unreacted compounds, so that the active medium provides a wide tuning range. The active medium may be a liquid or an amorphous solid, and in use is disposed in a cavity having a tuning reflector such as a rotatable diffraction grating, an acousto-optic grating, or an array of filters. Excitation may be by conventional optical pumping, or by particle excitation, field induced collision or chemical reaction. Exciplex formation.-Three basic ways of making an exciplex are described. In the first, a reaction occurs between an electron acceptordonor pair, either or both of the pair in the unreacted form being suitable for excitation to a lasing state. Examples of acceptors are unsubstituted polycyclic aromatic hydrocarbons having 2-5 rings, such as naphthalene, anthracene, pyrene, biphenyl, chrysene, and 1,1,4,4-tetraphenyl butadiene. The donor is a tertiary amine which may be of the form X-N-Y 2 where Y is an alkyl group and X is phenyl or naphthyl, or of the form Y 2 N-Z-NY 2 where Y is alkyl and Z is aromatic. The second basic method uses excimer formation, which involves a reaction between excited and unexcited molecules of a single material. Pyrene and its monochloro derivatives are the only known materials suitable. The third basic method uses protonation, for example of an indole, or of compounds of the general type As an example, a 5 x 10<SP>-3</SP> molar solution of 4- methyl-umbelliferone in ethanol was acidified by adding 1 part in 10 of 1 molar HCl. Lasing was achieved over a range of 4590-5740 Š when pumped by a pulsed nitrogen laser. Various pumping devices are instanced and may include optical and particle excitation, field induced collisions and chemical reactions.