  The aim of the present paper is twofold. The first goal is to show that high
resolution angle-resolved photoelectron spectra from cuprates indicate the
presence of string-like excitations of the quasihole excitation in a quantum
antiferromagnet. In order to compare with the experimental intensity plots, we
calculate the spectral function of the t-J and the t-t'-t"-J models within the
self-consistent Born approximation for widely accepted values of the parameters
of these models. The main features of the high resolution photoelectron spectra
are in general agreement with the results based on the above models and can be
understood by considering not only the lowest energy quasiparticle peak but,
also, the higher energy string-like excitations of the hole. The second goal of
the present paper is to make the case that a proper analysis of both the
numerical results obtained from these models and of the experimental results,
suggests a theoretical picture for the internal structure of the
hole-quasiparticle and a string-exchange pairing mechanism due to strong
antiferromagnetic correlations among the background spins. We find that, using
a simple model in which the Hilbert space is restricted to states of only
unbroken strings attached to the holes and in which the holes are connected
with unbroken strings, we can provide a good quantitative description of the
most accurate numerical results. We find that the holes experience an effective
interaction due to a string-exchange mechanism which is characterized by a
rather large string tension and this can provide pairing energy scales much
larger that those suggested by spin-fluctuation mediated pairing models. In
addition, it is argued that such string-exchange interaction tends to bind
holes in a bound state with the $d_{x^2-y^2}$ symmetry.
