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Probing matter with light in the mid-infrared provides unique insight into molecular composition, structure, and function with high sensitivity. However, laser spectroscopy in this spectral region lacks the broadband or tunable light sources and efficient detectors available in the visible or near-infrared. We overcome these challenges with an approach that unites a compact source of phase-stable, single-cycle, mid-infrared pulses with room temperature electric field–resolved detection at video rates. The ultrashort pulses correspond to laser frequency combs that span 3 to 27 μm (370 to 3333 cm−1), and are measured with dynamic range of >106 and spectral resolution as high as 0.003 cm−1. We highlight the brightness and coherence of our apparatus with gas-, liquid-, and solid-phase spectroscopy that extends over spectral bandwidths comparable to thermal or infrared synchrotron sources. This unique combination enables powerful avenues for rapid detection of biological, chemical, and physical properties of matter with molecular specificity.

We present the state of the art of a compact high-energy midinfrared laser system for TW-level 8-cycle pulses at 7 µm. This system consists of an Er:Tm:Ho:fiber MOPA which serves as the seeder for a ZGP-based OPCPA chain in addition to a Ho:YLF amplifier which is Tm:fiber pumped. Featuring all-optical synchronization, the system delivers 260-mJ pump energy at 2052 nm, 16-ps duration at 100 Hz with a stability of 0.8 % rms over 20 min. We show that chirp inversion in the OPCPA chain leads to excellent energy extraction and aids in compression of the 7-µm pulses to 8 optical cycles (188 fs) in bulk BaF 2 with 93.5 % efficiency. Using 21.7 mJ of the available pump energy, we generate 0.75-mJ-energy pulses at 7 µm due to increased efficiency with a chirp-inversion scheme. The pulse quality of the system's output is shown by generating high harmonics in ZnSe which span up to harmonic order 13 with excellent contrast. The combination of the passive carrier-envelope phase stable midinfrared seed pulses and the high-energy 2052 nm picosecond pulses makes this compact system a key enabling tool for the next generation of studies on extreme photonics, strong field physics and table-top coherent X-ray science.

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We report on the nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the theory provides insight into the carrier scattering dynamics and allows us to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between nonlinear optical response and microscopic dynamics provides a powerful methodology to study quantum phase transitions in correlated materials. Further implications are light wave control over intricate quantum phases, light–matter hybrids, and application for optical quantum computing.

BaGa2GeSе6 (BGGSe) is a newly developed nonlinear material which is attractive for ultrabroad frequency mixing and ultrashort pulse generation due to its comparably low dispersion and high damage threshold. A numerical study shows the material's capacity for octave spanning mid-infrared pulse generation up to 18 µm. In a first experiment, we show that a long crystal length of 2.6 mm yields a pulse energy of 21 pJ at 100 MHz and with a spectral bandwidth covering 5.8 to 8.5 µm. The electric field of the carrier-envelope-phase stable pulse is directly measured with electro optical sampling and reveals a pulse duration of 91 fs which corresponds to sub-4 optical cycles, thus confirming some of the prospects of the material for ultrashort pulse generation and mid-IR spectroscopy.

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We report on the new non-linear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase, and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a novel strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the new theory provides insight into the carrier scattering dynamics and allows to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between non-linear optical response and microscopic dynamics provides a powerful new methodology to study quantum phase transitions in correlated materials. Further implications are light-wave control over intricate quantum phases, light-matter hybrids, and application for optical quantum computing.