Anomalous laser energy absorption associated with resonance saturation

Laser energy absorption measurements have been undertaken in an experiment involving the transmission of a pulse of laser radiation through sodium vapour. The wavelength of the laser was tuned to overlap the 589 nm resonance transition of the sodium atoms. Although simple radiation transport appears to account for the attenuation of the laser beam at low values of incident laser irradiance, anomalously large absorption has been observed at high values of incident laser energy. We suggest that this anomalous absorption of laser energy can be regarded as evidence of superlastic electron heating and subsequent ionization.