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 Å (ground state 4S_1/2–4P_1/2) transition. Because linear and nonlinear dispersion delays may be confused with delays arising from self-induced transparency^4,5 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 Å to 11,000 Å 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 material^2,3.