Dual comb operation of λ ∼ 8.2 μm quantum cascade laser frequency comb with 1 W optical power

In this work, we report the characterization of a quantum cascade laser frequency comb with an optical power of 1.05 W at λ∼8.2 μm. A 4.5 mm long device has a high reflectivity coating on the back facet as well as a top cladding designed to lower the group velocity dispersion and is operated at 258 K. Very strong (more than 60 dB) narrow beatnotes are shown, and frequency comb operation is obtained on a bandwidth of 85 cm⁻¹ in a very large range of light-versus current characteristics. A bandwidth of 82 cm⁻¹ has a power per mode of more than 1 mW and an average power per mode of 4.1 mW. Finally, a multi-heterodyne spectrum with 215 lines covering an optical bandwidth of more than 70 cm⁻¹ measured with lasers showing similar performances is presented with very good line separation.