The information exchange dynamics between different spatial scales of a turbulent
field is experimentally investigated, with particular reference to the energy cascade
process. This is done by use of the collective light scattering (CLS) diagnostic, a
new optical setting tuned for the observation of atomic number density fluctuations
at macroscopic scales. A two-channel scattering device is described that provides
simultaneously the fluctuations at two different spatial scales. The turbulent system is
an axisymmetric air jet. With this system, time correlations between signal amplitudes
for two different scales show a characteristic time width. This time does not depend on
the observed scales: it is close to the turbulence production time. Nevertheless, signal
amplitude autocorrelation shows a shorter characteristic time. The autocorrelation
time scaling law behaves almost like the eddy turnover time from Kolmogorov theory.