Self-induced Transparency and Dispersion Delays in Potassium Vapour

Abstract

SELF-INDUCED transparency1 first demonstrated in ruby2 was subsequently reported3 observed in gaseous SF6. We wish to report the observation of this nonlinear transparency effect in the propagation through potassium vapour of coherent pulses of an organic dye laser, tuned to resonance with the λ7699 A (ground state 4S1/2–4P1/2) transition. Because linear and nonlinear dispersion delays may be confused with delays arising from self-induced transparency4,5 we have also investigated dispersion effects at frequencies away from resonance. The dye laser frequency can be readily tuned6 to resonance with transitions between single pairs of energy levels coupled to the laser field by dipole matrix elements, so complexities arising from degenerate transitions5 are avoided. Dye lasers covering the spectral range 3000 A to 11,000 A are now available and nonlinear coherent pulse propagation effects can thus be studied in many absorbing atomic vapours with our experimental arrangement which does not depend on the chance coincidence of a gas or solid-state laser frequency with a suitable electric-dipole transition in the material2,3.