Vibrational strong coupling (VSC) has recently emerged as a completely new tool for influencing chemical reactivity. It harnesses electromagnetic vacuum fluctuations through the creation of hybrid states of light and matter, called polaritonic states, in an optical cavity resonant to a molecular absorption band. Here, we investigate the effect of vibrational strong coupling of water on the enzymatic activity of pepsin, where a water molecule is directly involved in the enzyme's chemical mechanism. We observe an approximately 4.5‐fold decrease of the apparent second‐order rate constant k_cat/K_m when coupling the water stretching vibration, whereas no effect was detected for the strong coupling of the bending vibration. The possibility of modifying enzymatic activity by coupling water demonstrates the potential of VSC as a new tool to study biochemical reactivity.

Spectroscopy in the wavelength range from 2 to 11 μm (900 to 5000 cm⁻¹) implies a multitude of applications in fundamental physics, chemistry, as well as environmental and life sciences. The related vibrational transitions, which all infrared-active small molecules, the most common functional groups, as well as biomolecules like proteins, lipids, nucleic acids, and carbohydrates exhibit, reveal information about molecular structure and composition. However, light sources and detectors in the mid-infrared have been inferior to those in the visible or near-infrared, in terms of power, bandwidth, and sensitivity, severely limiting the performance of infrared experimental techniques. This article demonstrates the generation of femtosecond radiation with up to 5 W at 4.1 μm and 1.3 W at 8.5 μm, corresponding to an order-of-magnitude average power increase for ultrafast light sources operating at wavelengths longer than 5 μm. The presented concept is based on power-scalable near-infrared lasers emitting at a wavelength near 1 μm, which pump optical parametric amplifiers. In addition, both wavelength tunability and supercontinuum generation are reported, resulting in spectral coverage from 1.6 to 10.2 μm with power densities exceeding state-of-the-art synchrotron sources over the entire range. The flexible frequency conversion scheme is highly attractive for both up-conversion and frequency comb spectroscopy, as well as for a variety of time-domain applications.

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Spectral broadening in bulk material is a simple, robust and low-cost method to extend the bandwidth of a laser source. Consequently, it enables ultrashort pulse compression. Experiments with a 38 MHz repetition rate, 50 W average power Kerr-lens mode-locked thin-disk oscillator were performed. The initially 1.2 μJ, 250 fs pulses are compressed to 43 fs by means of self-phase modulation in a single 15 mm thick quartz crystal and subsequent chirped-mirror compression. The losses due to spatial nonlinear effects are only about 40 %. A second broadening stage reduced the Fourier transform limit to 15 fs. It is shown that the intensity noise of the oscillator is preserved independent of the broadening factor. Simulations manifest the peak power scalability of the concept and show that it is applicable to a wide range of input pulse durations and energies.

Waveform-stabilized laser pulses have revolutionized the exploration of the electronic structure and dynamics of matter by serving as the technological basis for frequency-comb and attosecond spectroscopy. Their primary sources, mode-locked titanium-doped sapphire lasers and erbium/ytterbium-doped fibre lasers, deliver pulses with several nanojoules energy, which is insufficient for many important applications. Here we present the waveform-stabilized light source that is scalable to microjoule energy levels at the full (megahertz) repetition rate of the laser oscillator. A diode-pumped Kerr-lens-mode-locked Yb:YAG thin-disk laser combined with extracavity pulse compression yields waveform-stabilized few-cycle pulses (7.7 fs, 2.2 cycles) with a pulse energy of 0.15 μJ and an average power of 6 W. The demonstrated concept is scalable to pulse energies of several microjoules and near-gigawatt peak powers. The generation of attosecond pulses at the full repetition rate of the oscillator comes into reach. The presented system could serve as a primary source for frequency combs in the mid infrared and vacuum UV with unprecedented high power levels.