Abstract

If ${\text{O}}_{2`}^{-}$ centers in KCl are excited in their fundamental absorption band (at about 250 nm), they yield a fluorescnece spectrum which at low temperatures is dominated by a progression of very narrow zero-phonon lines (Δν_1/2≈1cm⁻¹) with a large Stokes shift (roughly 23000 cm⁻¹ or 2.9 eV). At very high excitation intensities (≳ 20 GW/cm²) with single pulses of the fourth harmonic of a modelocked Nd-YAG laser (λ = 266 nm, pulse duration 30 ps, pulse energy ~ 100 μJ) and at low temepratures (T < 30 K) one observes a simultaneous coherent emission at the wavelength of two of the zero-phonon lines (0-10 and 0-11 transition at 594.77 and 629.14 nm, respectively) /1/, which can be identified as two-color superfluorescence fron a three-level system /2,3/.

© 1984 Optical Society of America