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Single-mode operation of Fabry-Perot quantum cascade (QC) lasers is achieved through the systematic shortening of the cavity length from 764 to 110 μm. The increased mirror loss is mitigated using highly reflective (HR) metallic facet coatings (R >; 95%). Ultrashort cavity QC lasers operate single mode with the best device having a mode-hop free current tuning range of 3.44 cm-1. Using combined heat-sink temperature and current tuning, the largest single-mode tuning range attained was 8.56 cm-1. The heat dissipation of a 110-μm ultrashort cavity QC laser is 0.23 W at 80 K and 0.43 W at 150 K. With a 500-μm cavity and both facets HR coated with reflectivities of ~95% and 75%, room-temperature continuous wave operation is realized with heat dissipation of 1.2-1.7 W.