The Ring Dye Laser as a Source for Two-Photon Excited Fluorescence

ABSTRACT The near-Gaussian beam profile, low pulse-to-pulse amplitude fluctuation and amenability to simple signal processing make synchronously-pumped dye lasers, both continuous and cavity-dumped, excellent sources for two-photon spectroscopy. In recent years attention has shifted from the more common standing wave configuration to a traveling wave ring laser of synchronous length. The continuous variant has proven to be a source with a detectivity for two-photon excited fluorescence equal to the cavity-dumped, standing wave laser but without the added optical and electronic complexity of the Bragg cell. However, cavity gain/loss, bandwidth and length changes influence pulse characteristics to a different extent than in standing wave lasers. These effects are discussed relative to both the two-color, two-photon experiment and overall instrumental design considerations.