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Femtosecond laser sources and optical frequency combs in the molecular fingerprint region of the electromagnetic spectrum are crucial for a plethora of applications in natural and life sciences. Here we introduce Cr 2-based lasers as a convenient means for producing super-octave mid-IR electromagnetic transients via optical rectification (or intra-pulse difference frequency generation, IDFG). We demonstrate that a relatively long, 2.5 μm, central wavelength of a few-cycle Cr 2 :ZnS driving source (20 fs pulse duration, 6 W average power, 78 MHz repetition rate) enabled the use of highly nonlinear ZnGeP 2 crystal for IDFG with exceptionally high conversion efficiency (>3%) and output power of 0.15 W, with the spectral span of 5.8-12.5 μm. Even broader spectrum was achieved in GaSe crystal: 4.3-16.6 μm for type I and 5.8-17.6 μm for type II phase matching. The results highlight the potential of this architecture for ultrafast spectroscopy and generation of broadband frequency combs in the longwave infrared.