In the 2015 review paper ‘Petawatt Class Lasers Worldwide’ a comprehensive overview of the current status of high-power facilities of ${>}200~\text{TW}$ was presented. This was largely based on facility specifications, with some description of their uses, for instance in fundamental ultra-high-intensity interactions, secondary source generation, and inertial confinement fusion (ICF). With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification (CPA), which made these lasers possible, we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed. We are now in the era of multi-petawatt facilities coming online, with 100 PW lasers being proposed and even under construction. In addition to this there is a pull towards development of industrial and multi-disciplinary applications, which demands much higher repetition rates, delivering high-average powers with higher efficiencies and the use of alternative wavelengths: mid-IR facilities. So apart from a comprehensive update of the current global status, we want to look at what technologies are to be deployed to get to these new regimes, and some of the critical issues facing their development.

We have achieved very efficient high-harmonic generation in a two-color laser field using a long gas jet of He. With the optimization of laser parameters and target conditions, strong harmonics were produced at 2͑2n +1͒th orders in an orthogonally polarized two-color field. The strongest harmonic at the 38th order ͑21.6 nm͒ reached an energy of 0.6 J with a 6 mm gas jet, giving a conversion efficiency as high as 2 ϫ 10 −4 .

To generalize the applicability of the temporal characterization technique called “tunneling ionization with a perturbation for the time-domain observation of an electric field” (TIPTOE), the technique is examined in the multicycle regime over a broad wavelength range, from the UV to the IR range. The technique is rigorously analyzed first by solving the time-dependent Schrödinger equation. Then, experimental verification is demonstrated over an almost 5-octave wavelength range at 266, 1800, 4000 and 8000 nm by utilizing the same nonlinear medium – air. The experimentally obtained dispersion values of the materials used for the dispersion control show very good agreement with the ones calculated using the material dispersion data and the pulse duration results obtained for 1800 and 4000 nm agree well with the frequency-resolved optical gating measurements. The universality of TIPTOE arises from its phase-matching-free nature and its unprecedented broadband operation range.

No abstract

The polarization of high-harmonics from aligned N(2) molecules was measured by observing the visibility of spatial interference between two high-harmonics generated separately. The minimum visibility was observed at an angle of 60 degrees between the polarization of the harmonic generation laser field and the molecular orientation. In this case, the angular shift of harmonic polarization is 15 degrees from the molecular orientation. Our measurement of the visibility variation matches the theoretical prediction based on the harmonic field calculation for aligned N(2) molecules.

Characteristics of high harmonics generated from aligned N 2 molecules were investigated by rotating the molecules with respect to the polarization of harmonic generation pulses. The high harmonics in the plateau and the cutoff regions showed distinctive behaviour, which could be explained from the calculation of transition dipole moments between recolliding electron and multi-orbitals of N 2 molecule consisting of the highest occupied molecular orbital (HOMO) and the lower-lying orbital below HOMO (HOMO-1). It was also observed that the angular dependence of harmonics from aligned molecules with respect to the polarization of harmonic generation pulses was closely related to the geometrical structure of molecular orbitals, and that the harmonic in the transition region from the plateau to the cutoff was influenced comparably by both HOMO and HOMO-1. These results confirmed that high harmonic generation and molecular structure were closely linked.

Throughout an individual’s lifetime, genomic alterations accumulate in somatic cells1–11. However, the mutational landscape induced by retrotransposition of long interspersed nuclear element-1 (L1), a widespread mobile element in the human genome12–14, is poorly understood in normal cells. Here we explored the whole-genome sequences of 899 single-cell clones established from three different cell types collected from 28 individuals. We identified 1,708 somatic L1 retrotransposition events that were enriched in colorectal epithelium and showed a positive relationship with age. Fingerprinting of source elements showed 34 retrotransposition-competent L1s. Multidimensional analysis demonstrated that (1) somatic L1 retrotranspositions occur from early embryogenesis at a substantial rate, (2) epigenetic on/off of a source element is preferentially determined in the early organogenesis stage, (3) retrotransposition-competent L1s with a lower population allele frequency have higher retrotransposition activity and (4) only a small fraction of L1 transcripts in the cytoplasm are finally retrotransposed in somatic cells. Analysis of matched cancers further suggested that somatic L1 retrotransposition rate is substantially increased during colorectal tumourigenesis. In summary, this study illustrates L1 retrotransposition-induced somatic mosaicism in normal cells and provides insights into the genomic and epigenomic regulation of transposable elements over the human lifetime.

We theoretically investigate the process of high-order harmonic generation (HHG) in an intense two-colour femtosecond laser field, of which both fundamental field and its second harmonic are linearly polarized. With the second harmonic field added, new degrees of freedom become available for controlling the process—relative phase between the two components and angle between the two polarization axes. It is shown that these parameters can be adjusted so as to select an electron path contributing to the process, leading to HHG from either a short path or a long path. As a result of this selectivity, regular and strong attosecond pulses can be generated.