  The effects of microwave radiation on the transport properties of atomically
thin $La_{2-x}Sr_xCuO_4$ films were studied in the 0.1-13 GHz frequency range.
Resistance changes induced by microwaves were investigated at different
temperatures near the superconducting transition. The nonlinear response
decreases by several orders of magnitude within a few GHz of a cutoff frequency
$\nu_{cut} \approx$ 2 GHz. Numerical simulations that assume an ac response to
follow the dc V-I characteristics of the films reproduce well the low frequency
behavior, but fail above $\nu_{cut}$. The results indicate that two-dimensional
superconductivity is resilient against high-frequency microwave radiation,
because vortex-antivortex dissociation is dramatically suppressed in
two-dimensional superconducting condensates oscillating at high frequencies.
