We report the generation of extremely broadband and inherently phase-locked mid-infrared pulses covering the 5 to 11 µm region. The concept is based on two stages of optical parametric amplification starting from a 270-fs Yb:KGW laser source. A continuum seeded, second harmonic pumped pre-amplifier in β-BaB 2 O 4 (BBO) produces tailored broadband near-infrared pulses that are subsequently mixed with the fundamental pump pulses in LiGaS 2 (LGS) for mid-infrared generation and amplification. The pulse bandwidth and chirp is managed entirely by selected optical filters and bulk material. We find an overall quantum efficiency of 1% and a mid-infrared spectrum smoothly covering 5-11 µm with a pulse energy of 220 nJ at 50 kHz repetition rate. Electro-optic sampling with 12-fs long white-light pulses directly from self-compression in a YAG crystal reveals near-single-cycle mid-infrared pulses (32 fs) with passively stable carrier-envelope phase. Such pulses will be ideal for producing attosecond electron pulses or for advancing molecular fingerprint spectroscopy.

A dielectric material’s response to light is microscopically defined by field-cycle-driven motion of electron densities in the restoring forces of the atomic environment. Here we apply single-cycle mid-infrared pulses to drive the nonlinear motion of valence electrons in a heteronuclear crystal with asymmetric structure and report how the macroscopic optical response can be tracked back to the real-space electron dynamics in the symmetry-breaking potential along the chemical bonds. Whether our single-cycle field drives electrons from the less electronegative to the more electronegative element or vice versa controls the appearance of a smooth nonlinear output spectrum or one with even and odd harmonic orders. Crystal angle scans reveal the absolute orientation of the asymmetric bonds. Directional motion of valence charges controlled by a single cycle of light can therefore be used for spectroscopically exploring the binding potential, to understand and design novel materials for nonlinear optics, or to eventually process information at the frequency of light.

Near-single-cycle mid-infrared pulses with a spectrum covering 5.4-11 μm are efficiently frequency-doubled in different GaSe crystals. The second-harmonic spectrum spans 3-4.3 μm at a power conversion efficiency of >20%. We measure an effective nonlinear coefficient of d eff ≈ 35 pm∕V. We also report on self-phase modulation and spectral broadening of the mid-infrared pulses in various bulk materials and find an increase of 45% of spectral width for 5 mm of Ge. These results demonstrate that nonlinear optical conversions can efficiently be driven by few-cycle mid-infrared radiation.