Flat‐Top Pumped Multi‐Millijoule Mid‐Infrared Parametric Chirped‐Pulse Amplifier at 10 kHz Repetition Rate.

The advancement of mid‐infrared (MIR) parametric amplification technique serves as the main driving force of multiple strong‐field experiments in the frontier of science such as the generation of coherent soft X‐ray and isolated attosecond pulses. However, the low parametric down‐conversion efficiency especially in the MIR wavelength is a major bottleneck that hinders the further exploration of the MIR‐laser‐driven strong‐field physics. Here, a simple and robust method that doubles the efficiency of a MIR optical parametric chirped‐pulse amplifier (OPCPA) is reported, as a demonstration of the concept, through engineering a flat‐top pump profile via high‐efficiency diffractive optical elements. With the proposed flat‐top pump scheme, a MIR OPCPA system at 3 μm and 10 kHz repetition rate with both the record pulse energy of 2.7 mJ and the highest average power at 27 W among the MIR OPCPAs with kHz repetition rate is demonstrated. This work provides a promising approach for achieving high energy high power MIR few‐cycle lasers that can be readily used in emerging strong field experiments. In addition, it is believed that the developed technique in this work can become a general method of parametric efficiency enhancement, which is applicable to other nonlinear conversions and wavelength ranges. [ABSTRACT FROM AUTHOR]