Extended Continuous Tuning of a Single-Frequency Diode-Pumped Vertical-External-Cavity Surface-Emitting Laser at 2.3 $\mu$ m

We report on single-frequency operation and wide mode-hop-free tuning range of a diode laser-pumped vertical-external-cavity surface-emitting semiconductor laser producing up to 3 mW around 2.3 mum. An optically stable external cavity of only 1.4 mm is formed using a concave dielectric mirror of 2-mm radius. The maximum continuous tuning is about 500 GHz wide, obtained by a synchronized ramp of external cavity length and of the gain medium temperature. We used this tunable source to record a direct absorption spectrum of methane, which is found to match well a simulated spectrum from the HITRAN (high-resolution transmission molecular absorption database http://www.cfa.harvard.edu/hitran) database.