External cavity cascade diode lasers tunable from 3.05 to 3.25 μm

The external cavity tunable mid-infrared emitters based on Littrow configuration and utilizing three stages type-I quantum well cascade diode laser gain elements were designed and fabricated. The free-standing coated 7.5-mu m-wide ridge waveguide lasers generated more than 30 mW of continuous wave power near 3.25 mu m at 20 degrees C when mounted epi-side-up on copper blocks. The external cavity lasers (ECLs) utilized 2-mm-long gain chips with straight ridge design and anti-/neutral-reflection coated facets. The ECLs demonstrated narrow spectrum tunable operation with several milliwatts of output power in spectral region from 3.05 to 3.25 mu m corresponding to similar to 25 meV of tuning range. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)