Lasers with Cr-doped II-VI gain media have recently evolved as new sources for ultrashort few-cycle pulses with wavelengths around 2 to 3 µm. Further nonlinear pulse compression and dispersion management with advanced multi-layer optics allow us to compress the output of our lasers down to true single-cycle pulse durations. To reach extremely low-noise laser performance, we directly pump our systems with low-noise light sources and actively stabilize the output waveforms. Further down-conversion to the mid-infrared spectral range results in multi-octave-spanning mid-infrared continua that maintain the single-cycle pulse durations of the driving pulses. 

As a pulse approaches durations of just a single oscillation cycle, traditional methods of characterization and control reach their limits: when the interaction with matter depends on the intricate details of the time-dependent field, we need a metrology capable of accessing this information. To this end, we develop new approaches to resolving the electric field of light, emphasizing sensitivity to weak fields for field-resolved spectroscopy and broadband detection for the observation of sub-cycle dynamics.

Having access to the full temporal evolution of the electric field allows a much finer-grained control in light-matter interactions. The first step towards this is to have a truly reproducible waveform, which we achieve through fundamentally stable laser sources with record levels of waveform stability. Once the field is reproducible, we can introduce additional levels of control, changing parameters such as the CEP, or by dividing the light into multiple channels and combining them individually. With feedback and control in place, we can form a multitude of user-selectable electric field waveforms, creating a platform for cutting edge experiments with unprecedented levels of control over the evolution of light-matter interaction.

With direct access to the electric field of light, we have access to a detailed history of how it interacted with materials like atoms, molecules, or solids, inscribed into it by the motion of charges. We know from Maxwell’s equations that a changing polarization influences the electric field, and by examining the resulting wave equations, and knowing exactly what the field was before and after the interaction, we have a detailed view of the underlying charge motion responsible. Likewise, knowing that resonant interactions provide a slowly-decaying polarization response, we can look for the corresponding electric field at moments in time where weak signals from dilute constituents of a mixture don’t have to compete with signals from the solvent or the laser pulse itself, greatly enhancing the sensitivity of spectroscopic measurements.