Structure and Properties of Laser Dyes

Abstract

An essential constituent of any laser is the amplifying medium which, in the context of this book, is a solution of an organic dye. Since the beginning, the development of the dye laser has been closely tied in with the discovery of new and better laser dyes. The phthalocyanine solution employed for the original dye laser (Sorokin and Lankard, 1966) is hardly used today, but the compound rhodamine 6G, found soon afterwards (Sorokin et al., 1967), is probably the most widely employed laser dye at the present time. In the years following the discovery of the dye laser various other compounds were reported for this purpose. Almost all were found by screening commercially available chemicals, but this source of new laser dyes soon became exhausted. It was reported in 1969 that a survey of approximately one thousand commercial dyes showed only four to be useful (Gregg and Thomas, 1969), and three of these belonged to classes of laser dyes that were already well known. Considering the large number of available chemicals, it is perhaps surprising that so few good laser dyes have been found so far. The reason for this is that some very special requirements must be met by such dyes and this excludes the majority of organic compounds. This chapter is intended to give the reader some insight into the relations between molecular structure and the lasing properties of organic dyes, relations which have recently been applied in the planned synthesis of new laser dyes. In addition, the physicochemical properties of the most important laser dyes are discussed here in some detail.