External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at ∼7.6 μm**Supported by the National Basic Research Program of China under Grant No 2013CB632801, the National Key Research and Development Program of China under Grant No 2016YFB0402303, the National Natural Science Foundation of China under Grant Nos 61435014, 61627822, 61574136, 61306058 and 61404131, the Key Projects of Chinese Academy

Abstract

An external cavity quantum cascade laser (QCL) array with a wide tuning range and high output power is presented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capability of 30.6 cm−1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications.