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A tunable external cavity laser (ECL) near 3.24 m was developed using semiconductor laser gain chips based on GaSb. The type-1 interband laser diodes were grown by molecular beam epitaxy using 17 nm InGaAsSb compressively-strained quantum wells with 30 nm AlInGaAsSb quinary barriers for improved hole confinement. In continuous-wave operation with a diode temperature of 10 C, the ECLs produce up to 1.8 mW of singlemode output power with a tuning range of 60 nm. The devices are tunable through the fundamental 3 vibrational absorption features of methane gas, providing a platform for highly-sensitive detection of trace hydrocarbons.