  An ensemble of neutral excitations is constructed experimentally in the
Laughlin liquid at the electron filling factor 1/3. The excitations are found
to induce a nonlinear optical response, manifested as a quadratic dependence of
the reflection signal on the excitation power. The reported experimental
results indicate that the observed effect is due to the contribution of the
coherent anti-Stokes-Stokes scattering of light from the excited Laughlin
liquid.
