  The nature of the underdoped pseudogap regime of the high-temperature
superconductors has been a matter of long-term debate. On quite general
grounds, one expects that due to their low superfluid densities and short
correlation lengths, superconducting fluctuations will be significant for
transport and thermodynamic properties in this part of the phase diagram.
Although there is ample experimental evidence for such correlations, there has
been disagreement about how high in temperature they may persist, their role in
the phenomenology of the pseudogap, and their significance for understanding
high-temperature superconductivity. In this work we use THz time-domain
spectroscopy (TTDS) to probe the temporal fluctuations of superconductivity
above the critical temperature (T$_c$) in La$_{2-x}$Sr$_x$CuO$_4$ thin films
over a doping range that spans almost the entire superconducting dome (x = 0.09
to 0.25). Signatures of the fluctuations persist in the conductivity in a
comparatively narrow temperature range, at most 16 K above Tc. Our measurements
show that superconducting correlations do not make an appreciable contribution
to the charge transport anomalies of the pseudogap in LSCO at temperatures well
above T$_c$.

Superconductivity