Dyes for cw infrared output

Polymethine (carbocyanine) dyes for cw lasers operating in the near IR (700 to 1000 nm) with excitation of red output from a krypton laser are discussed. In contrast to the rigid planar structures of the coumarines, xanthenes, and oxazines covering the visible spectrum, the polymethines exhibit long chainlike molecules with conjugated double bonds along the chain. A simplified model treats the pi-electrons of the conjugated double bonds as a one-dimensional free-electron gas, facilitating analysis of the potential well problem. Variant end-group structures and substitutions and their practical effects are discussed. Indocarbocyanines or oxacarbocyanines are under consideration as dyes for the region longward of 1000 nm. Applications in research on semiconductor materials, isotope separation, laser chemistry, environmental monitoring, and surgery are contemplated.