Scaling of dye lasers with improved laser dyes

Dye lasers are widely used in spectroscopic research because they provide tunable, coherent radiation. They employ highly fluorescent organic compounds, possessing some specific spectroscopic properties, dissolved in organic solvents. These liquid media are cooled by circulation. The liquid media, the dye solutions, have no scaling limitation. However, large dye lasers that generate high-energy and high average-power outputs do not exist because of the lack of a scalable pump source. Presently, pulsed and CW lasers and short-pulse small flashlamp are mainly used for pumping laser dyes. Only these pump sources are able to overcome the excessive triplet-state losses (TSLs) present in presently available laser dyes. These TSLs result, in part, from fairly large triplet absorption coefficients, εT(λF), of transient triplet-state dye molecules generated during excitation. Using new laser dyes that possess smaller triplet absorption coefficients should not only improve laser-action efficiencies, but should also allow pumping with large, long-pulse flashlamps and possibly with laser diode arrays and incoherent light sources. These pump sources are scalable and therefore would further increase overall outputs. This paper details TSL, vibronic spin–orbit interactions in heterocyclics, and other spectroscopic parameters affecting laser-action properties. Pump sources for dye lasers, especially flashlamps, are also reviewed. Criteria that can be used to identify candidate laser dyes for efficient long-pulse operation are provided. These are the so-called quasi-aromatics (QAs), five- and six-membered heterocyclics, and are identified as possessing small εT(λF) values. The pyrromethene–BF2 complexes are representatives of such QAs. There should be many candidates that exhibit efficient laser action in different spectral regions, under long-pulse, large flashlamp pumping.