The effects of optical feedback on a terahertz (THz) quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) are investigated via self-mixing. A nominally single-mode 2.8 THz QC-VECSEL operating in continuous-wave is subjected to various optical feedback conditions while monitoring variations in its terminal voltage associated with self-mixing. Due to its large emitting aperture, and flat highly-reflective output coupler, the VECSEL architecture is found to be strongly susceptible to optical feedback. Regions of instability are observed, as is evidence of multiple roundtrip re-injection within the feedback cavity.
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Kim et al. (2024) studied this question.
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