External cavity spectrum beam combining based on quantum cascade laser array

Abstract

Spectral beam combining (SBC) is a regular approach of utilizing semiconductor laser arrays, as it can greatly improve output power and maintain the beam quality. External cavity spectral beam combining based on the six elements quantum cascade laser (QCL) array, with a 10μm ridge width and a pitch of 60μm, was realized. The divergence of the light from output coupler is 0.6mrad and 3.8mrad, for fast axis (perpendicular to the array) and slow axis (parallel to the array), respectively. Under a condition of 10kHz repetition frequency and 1μ s pulse width, the array’s peak power is 2.9W without SBC system. The peak power of 0.9W and 1.34W is achieved when utilizing a output coupler based on Ge without anti-reflection (AR) coating or with AR coating, respectively. Corresponding the beam combining efficiency is 31.0% and 46.2%, respectively. We recorded the cross-locking phenomenon when tuning array by rotating the external cavity output coupler angle, as a relatively close element spacing results in mutual locking of adjacent elements. The system could tuning over 99cm-1 (1904cm-1--2003cm-1).