COHERENT FAN EMISSIONS

A transient grating is induced at t = 0 in an optically thin caesium v apour sample using two simultaneous intense short laser pulses which a re resonant with the fundamental 6S(1/2)-6P(1/2) transition and charac terized by the wavevectors (k) over right arrow(1) and (k) over right arrow(2). These pulses are followed by a third resonant excitation pul se at t = tau with wavevector (k) over right arrow(3). Prompt and dela yed super-radiant emissions follow with a spatial pattern governed by higher-order diffraction effects. We study the polarization and modula tion properties of these coherent fan emissions.