  Free-running Fabry-Perot lasers normally operate in a single-mode regime
until the pumping current is increased beyond the single-mode instability
threshold, above which they evolve into a multimode state. As a result of this
instability, the single-mode operation of these lasers is typically constrained
to few percents of their output power range, this being an undesired limitation
in spectroscopy applications. In order to expand the span of single-mode
operation, we use an optical injection seed generated by an external-cavity
single-mode laser source to force the Fabry-Perot quantum cascade laser into a
single-mode state in the high current range, where it would otherwise operate
in a multimode regime. Utilizing this approach we achieve single-mode emission
at room temperature with a tuning range of $36 \, \mathrm{cm}^-1$ and stable
continuous-wave output power exceeding 1 W. Far-field measurements show that a
single transverse mode is emitted up to the highest optical power indicating
that the beam properties of the seeded Fabry-Perot laser remain unchanged as
compared to free-running operation.
