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