Watt-level widely tunable single-mode emission by injection-locking of a multimode Fabry-Perot quantum cascade laser

TL;DR

This paper demonstrates a method to achieve watt-level, widely tunable, single-mode emission from a multimode Fabry-Perot quantum cascade laser by using injection-locking, significantly expanding its single-mode operational range for spectroscopy.

Contribution

The authors introduce an injection-locking technique to stabilize single-mode operation in high-power quantum cascade lasers, overcoming the typical multimode instability at high currents.

Findings

Achieved room-temperature single-mode emission with 36 cm^-1 tuning range.

Produced stable continuous-wave output power exceeding 1 W.

Maintained beam quality with a single transverse mode at high power.

Abstract

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.