  Fundamental optical properties of thin films of (Ga,Mn)As diluted
ferromagnetic semiconductor with a low (1%) and high (6%) Mn content and of a
reference GaAs film, grown by low-temperature molecular-beam epitaxy, have been
investigated by photoreflectance (PR) spectroscopy. In addition, the films were
subjected to complementary characterization by means of superconducting quantum
interference device (SQUID) magnetometry, Raman spectroscopy, and high
resolution X-ray diffractometry. Thorough full-line-shape analysis of the PR
spectra, which enabled determination of the E0 electronic transition in
(Ga,Mn)As, revealed significant differences between the energy band structures
in vicinity of the {\Gamma} point of the Brillouin zone for the two (Ga,Mn)As
films. In view of the obtained experimental results the evolution of the
valence band structure in (Ga,Mn)As with increasing Mn content is discussed,
pointing to a merging the Mn-related impurity band with the host GaAs valence
band for high Mn content.
