Characteristics of organic dye lasers as tunable frequency sources for nanosecond absorption spectroscopy

The properties of 1, 1\´ diethyl-γ-cyano-2,2\´-di-carbocyanine-tetrafluoroborate (DTCDCT)and 1, 1\´-diethyl-γ-nitro- 4, 4\´-di-carbocyanine-tetrafluoroborate (DTNDCT) lasers have been investigated. High-efficiency (25 percent) spectral narrowing of the normal 150-Å-wide, 2-MW output of DTCDCT (around λ 7600 Å) to <0.01 Å, corresponding to a single longitudinal mode, is achieved with a novel longitudinally pumped (by giant pulse ruby laser) dye laser cavity. Beam divergence is <0.5 mrad, and spectral tunability is obtained by rotating the echelle grating and Fabry-Perot etalon cavity elements. DTNDCT transversely pumped by a mode-locked ruby laser (>150 MW peak power) produces a train of 100 percent modulated mode-locked dye laser pulses whose risetimes (<0.5 ns) and pulse widths (0.6 ns) are detector limited. The production of broad continua for nanosecond absorption spectroscopy is also described, together with measurements on the synchronization of the pumping and dye laser pulses. Finally, the direct spectrographic detection of near-resonant optical-frequency Stark effects in potassium is briefly described. Employing the DTCDCT continuum as absorption source, a red shift of cm^-1of the λ 7699-Å resonance line was detected for a ruby laser perturbing field of power density ∼ 30 MW/cm^-2.