Observation of a 1.9-psec polarization beat

We have observed polarization beats by simultaneously exciting both the D1 (589.6-nm) and the D2 (589-nm) lines of sodium in a vapor with a 0.4-psec resonant laser pulse. This impact excitation of both D lines produces two oscillating macroscopic polarizations, which interfere with each other and procedure a beat note at their difference frequency in the intensity of the light emitted from the cell. The beat period of 1.9 psec is the fastest ever observed optically. © 1985, Optical Society of America.