INTENSITY FLUCTUATIONS IN A LASER-BEAM DUE TO PROPAGATION THROUGH A PLANE TURBULENT JET

A planar heated air jet was constructed. Its flow properties were char acterized and shown to be both reproducible and in good agreement with the results of turbulence theory. The optical properties of the jet w ere studied with the help of a 632.8 nm HeNe laser beam. Measurements of the random phase modulations imposed on the wavefront of the beam t raversing the jet were made and the results reported in a previous pap er. The intensity fluctuations arising in the beam were also measured and their spectra and variance determined at various distances from th e jet. The spectra behave like power laws with a slope of -1 at low te mporal frequencies and a slope of -8/3 at higher frequencies. This dua l power-law behaviour is attributed to the differential velocities wit hin the planar jet.