  Critical fluctuations have been studied in the microwave conductivity of
Bi_2Sr_2CaCu_2O_(8+\delta), Bi_2Sr_2Ca_2Cu_3O_(10+delta), and
YBa_2Cu_3O_(7-delta) thin films above T_c. It is found that a consistent
analysis of the real and imaginary parts of the fluctuation conductivity can be
achieved only if an appropriate wavevector or energy cutoff in the fluctuation
spectrum is taken into account. In all of the three underdoped superconducting
films one observes strong fluctuations extending far above T_c. The coherence
length inferred from the imaginary part of the conductivity exhibits the static
critical exponent nu = 1 very close to T_c, and a crossover to the region with
nu = 2/3 at higher temperatures. In parallel, our analysis reveals the absence
of the normal conductivity near T_c, i.e. fully opened pseudogap. Following the
crossover to the region with nu = 2/3, the normal conductivity is gradually
recovered, i.e. the closing of the pseudogap is monitored.
