  We have compiled a pseudo-snapshot data set of two-colour observations from
the Hubble Space Telescope archive for a sample of 53 rich LMC clusters with
ages 10^6-10^10 yr. We present surface brightness profiles for the entire
sample, and derive structural parameters for each cluster, including core
radii, and luminosity and mass estimates. Because we expect the results
presented here to form the basis for several further projects, we describe in
detail the data reduction and surface brightness profile construction
processes, and compare our results with those of previous ground-based studies.
The surface brightness profiles show a large amount of detail, including
irregularities in the profiles of young clusters (such as bumps, dips, and
sharp shoulders), and evidence for both double clusters and post core-collapse
(PCC) clusters. In particular we find power-law profiles in the inner regions
of several candidate PCC clusters, with slopes of approximately -0.7, but
showing considerable variation. We estimate that 20 +/- 7 % of the old cluster
population of the LMC has entered PCC evolution, a similar fraction to that for
the Galactic globular cluster system. In addition, we examine the profile of
R136 in detail and show that it is probably not a PCC cluster. We also observe
a trend in core radius with age that has been discovered and discussed in
several previous publications by different authors. Our diagram has better
resolution however, and appears to show a bifurcation at several hundred Myr.
We argue that this observed relationship reflects true physical evolution in
LMC clusters, with some experiencing small scale core expansion due to mass
loss, and others large scale expansion due to some unidentified characteristic
or physical process.
