  New results for electric dipole strength in the chain of even-even Calcium
isotopes with the mass numbers A = 40 - 54 are presented. Starting from the
covariant Lagrangian of Quantum Hadrodynamics, spectra of collective vibrations
(phonons) and phonon-nucleon coupling vertices for $J \leq 6$ and normal parity
were computed in a self-consistent relativistic quasiparticle random phase
approximation (RQRPA). These vibrations coupled to Bogoliubov two-quasiparticle
configurations (2q$\otimes$phonon) form the model space for the calculations of
the dipole response function in the relativistic quasiparticle time blocking
approximation (RQTBA). The results for giant dipole resonance in the latter
approach are compared to those obtained in RQRPA and to available data.
Evolution of the dipole strength with neutron number is investigated for both
high-frequency giant dipole resonance (GDR) and low-lying strength. Development
of a pygmy resonant structure on the low-energy shoulder of GDR is traced and
analyzed in terms of transition densities. A dependence of the pygmy dipole
strength on the isospin asymmetry parameter is extracted.
