Laser Dyes in Aerogels

Dyes used for tunable lasers are selected for their broad energy levels and efficient radiative transitions that span a wide spectrum from the near UV to the near IR. An important factor that decreases the quantum yield of this transition is intersystem crossing where some of the molecules raised to the first excited singlet state experience a change of spin due to perturbations and cross to the corresponding triplet state. The accumulation of dye molecules in the triplet state is an important problem for dye laser operation. In this dissertation, a new method of reducing the population of the triplet state was explored. Dye solutions were introduced into glass aerogels that have very small pores of nanometer size and extremely enhanced surface areas. The influence of the enhanced solid surface on the triplet population was investigated. The relaxation time of the triplet state was measured using frequency domain spectroscopy. Results indicate that the triplet lifetime decreases for dyes in aerogels; hence the surface interaction facilitates the relaxation. In a separate experiment, relative quantum efficiency measurements were made as a function of temperature. A significant increase in room temperature quantum efficiency was observed for solutions in aerogels. This result can be interpreted as a decrease in the triplet losses and the experiment independently verifies that the surface interaction helps to quench the triplet state population.