  We investigate the fusion barriers for reactions involving Ca isotopes
$\mathrm{^{40}Ca}+\mathrm{^{40}Ca}$, $\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$, and
$\mathrm{^{48}Ca}+\mathrm{^{48}Ca}$ using the microscopic time-dependent
Hartree-Fock theory coupled with a density constraint. In this formalism the
fusion barriers are directly obtained from TDHF dynamics. We also study the
excitation of the pre-equilibrium GDR for the
$\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$ system and the associated $\gamma$-ray
emission spectrum. Fusion cross-sections are calculated using the incoming-wave
boundary condition approach. We examine the dependence of fusion barriers on
collision energy as well as on the different parametrizations of the Skyrme
interaction.
