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Coherent control of transverse modes in semiconductor laser frequency combs via radio-frequency injection

Increasing the output power of semiconductor laser frequency combs, while maintaining a single-lobe far-field characteristic is of great interest for mid-infrared sensing applications. Broadening of the ridge waveguide represents the most common approach for power scaling, however, the excitement of higher-order transverse modes often limits general applicability. Here, we demonstrate that the coherent control of the longitudinal laser modes enables control over the transverse modes of a quantum cascade laser. Modulating the laser in a frequency range 60 ± 3 MHz above the free-running laser beatnote and applying modulation powers above 25 dBm provides reliable fundamental transverse mode operation, observable as single-lobe, Gaussian-like characteristic in the recorded far-field. Furthermore, coherent comb operation for both fundamental and higher-order transverse mode states is demonstrated.