  We investigated the effects of annealing on LaMnO$_3$ epitaxial thin films
grown by pulsed laser deposition and propose an efficient method of
characterizing their stoichiometry. Structural, magnetic, and optical
properties coherently indicate non-stoichiometric ferromagnetic and
semiconducting phases for as-grown LaMnO$_3$ films. By annealing in an
oxygen-reducing atmosphere, we recovered the antiferromagnetic and insulating
phases of bulk-like stoichiometric LaMnO$_3$. We show that non-destructive
optical spectroscopy at room temperature is one of the most convenient tools
for identifying the phases of LaMnO$_3$ films. Our results serve as a
prerequisite in studying LaMnO$_3$ based heterostructures grown by pulsed laser
deposition.
