We report on a thin-disk multipass amplifier for ultrashort laser pulses delivering an average output power of 1105 W. The amplifier was seeded by a Trumpf TruMicro5050 laser with a power of 80 W at a wavelength of 1030 nm, pulse duration of 6.5 ps, and repetition rate of 800 kHz. The energy of the amplified pulses is 1.38 mJ with a duration of 7.3 ps. The amplifier exhibits an optical efficiency of 44% and a slope efficiency of 46%. The beam quality was measured to be better than M²=1.25.

We report on an Yb:YAG thin-disk multipass laser amplifier delivering sub-8 ps pulses at a wavelength of 1030 nm with 1420 W of average output power and 4.7 mJ of pulse energy. The amplifier is seeded by a regenerative amplifier delivering 6.5 ps pulses with 300 kHz of repetition rate and an average power of 115 W. The optical efficiency of the multipass amplifier was measured to be 48% and the beam quality factor was better than M² = 1.4. Furthermore we report on the external second harmonic generation from 1030 nm to 515 nm using an LBO crystal leading to an output power of 820 W with 2.7 mJ of energy per pulse. This corresponds to a conversion efficiency of 70%. Additionally, 234 W of average power were obtained at the third harmonic with a wavelength of 343 nm.

A linear to radial and/or azimuthal polarization converter (LRAC) has been inserted into the beam delivery of a micromachining station equipped with a picosecond laser system. Percussion drilling and helical drilling in steel have been performed using radially as well as azimuthally polarized infrared radiation at 1030 nm. The presented machining results are discussed on the basis of numerical simulations of the polarization-dependent beam propagation inside the fabricated capillaries.

A resonant diffraction grating comprising a mirror, a dielectric layer and a high index corrugation at the layer-air interface is shown to exhibit off-Littrow the record diffraction efficiency of 99% in the -1st reflected order at 1064 nm wavelength thanks to the excitation of a leaky mode of the layer. Such high figure is obtained by a grating 5 to 10 times shallower than in current attempts to realize high efficiency all-dielectric gratings.

The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S–2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the α particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering1, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle2–5, in line with recent determinations of the proton charge radius6–9, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties.