Microjoule Sub-Two-Cycle Mid-Infrared Intrapulse-DFG Driven by 3- $\mu$ m OPCPA

We report a microjoule, 10.3 μm, mid-infrared (MIR) intrapulse difference frequency generation (IPDFG) in GaSe, driven by a 3 μm optical parametric chirped-pulse amplifier. The generated IPDFG pulse spanning from 7 to 15 μm in spectrum is measured with a pulse width of 60 fs, corresponding to 1.8 optical cycles. We experimentally confirmed that the spectral broadening of the driving pulses caused by the self-phase modulation in GaSe plays a crucial role in the process of IPDFG. To the best of our knowledge, this is the first exploration of IPDFG driven at 3 μm wavelength. It provides an approach to generate few-cycle long-wavelength MIR pulses, with the recent rapid development of the 3 μm driving sources.