GB1348648A - Lasers - Google Patents

Abstract

1348648 Luminescent materials and uses thereof WESTERN ELECTRIC CO Inc 14 May 1971 [15 May 1970] 14950/71 Heading C4S [Also in Division H1] A dye laser active medium comprises at least two ingredients, one of which is excitable to produce a first lasing species and the other of which undergoes a chemical reaction when excited to form an exciplex lasing species, i.e. an excited complex, each of the two lasing species exceeding 10 mole per cent of the total excited material. One material may furnish both ingredients, part of the material remaining unreacted on excitation and the rest of the material forming the exciplex. The use of an active medium having two such species present in significant proportions allows a broad tuning range. It is preferred that the peak emissions of the two species are separated by at least 500 Š to increase the tuning range, as in Specification 1,348,647. 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 acoustooptic 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.-The exciplex may be formed by any of the three methods described in Specification 1,348,647, but the reactant concentrations are chosen to prevent the reaction being complete. Thus a single laserable dye may provide both the first excited species and the exciplex species. A fourth method of forming exciplexes is also given, and depends on the dissociation of any aromatic compound having 1-5 aromatic rings and at least one -OH group on a ring, provided it does not have a nitro group or more than two halogen substituents. For the acceptor-donor method, some 20 mole per cent of an excitable ingredient is maintained; for excimer formation a dilute solution of 10<SP>-5</SP>-10<SP>-3</SP> M is used; for the protonation method the acidity is restricted, e.g. to 4-6 pH. For the dissociation method, base concentration is controlled. As an example of concentration control, the 4-methyl-umbelliferone of Specification 1,348,647 was made up as a 5 x 10<SP>-3</SP> M solution in ethanol, and acidified with 1 part in 30 of 0À1 M HCl. When pumped with a nitrogen laser the tuning range was from 3910 to 5670 A. Pumping devices are instanced, and may include optical and particle excitation, field induced collisions and chemical reactions.