5-μm vertical external-cavity surface-emitting laser (VECSEL) for spectroscopic applications

Mid-IR tunable VECSELs (Vertical External-Cavity Surface-Emitting Lasers) emitting at 4-7 mu m wavelengths and suitable for spectroscopic sensing applications are described. They are realized with lead-chalcogenide (IV-VI) narrow band gap materials. The active part, a single 0.6-2-mu m thick PbTe or PbSe gain layer, is grown onto an epitaxial Bragg mirror consisting of two or three Pb1-y Eu (y) Te/BaF2 quarter-wavelength layer pairs. All layers are deposited by MBE in a single run employing a BaF2 or Si substrate, no further processing is needed. The cavity is completed with an external curved top mirror, which is again realized with an epitaxial Bragg structure. Pumping is performed optically with a 1.5-mu m laser. Maximum output power for pulsed operation is currently up to > 1 W-p at -173A degrees C and > 10 mW at 10A degrees C. In continuous wave (CW) operation, 18 mW at 100 K are reached. Still higher operating temperatures and/or powers are expected with better heat-removal structures and better designs employing QW (Quantum-Wells). Advantages of mid-IR VECSELs compared to edge-emitting lasers are their very good beam quality (circular beam with < 1A degrees cone diameter), simple structure, and their easy tunability without mode-hopping. Wavelengths ranging from < 3 mu m up to > 15 mu m are accessible with Pb1-y X (y) Z (X=Sr, Eu, Sn, Z=Se, Te) and/or including QW.