Maximizing the efficiency of intrapulse difference frequency generation by pulse shaping and recycling

Intrapulse Difference Frequency Generation (iDFG) is an interesting technique for generating femtosecond pulses in the Mid-Infrared (MIR) range with unique properties such as robust Carrier-Envelope Phase (CEP) stability. However, its efficiency is low compared to other techniques. In this paper, we describe an iDFG system operating within the 4–10 μm range that features an original architecture to enhance efficiency. First, we introduce an interesting technique on the generation process. This approach involves polarization and spectral phase shaping techniques on the driving pulse to maximize the number of photons enrolled in the process. Second, we demonstrate that the polarization shaping allows further enhancement of efficiency by recycling the iDFG signal to pump a subsequent optical parametric amplification (OPA) stage. These two concepts and the associated parameters optimization are described into details, and supported by experimental results. Combined with a high-power Yb-fiber-based pump laser, these techniques allow to achieve record efficiencies, and generate μJ-level, few-cycle, tunable, CEP-stable pulses in the MIR at repetition rates above 100 kHz.