We present a table-top coherent diffraction imaging (CDI) experiment based on high-order harmonics generated at 18 nm by a high average power femtosecond fiber laser system. The high photon flux, narrow spectral bandwidth and high degree of spatial coherence allow for ultra-high sub-wavelength resolution imaging at a high numerical aperture. Our experiments demonstrate a half-pitch resolution of 13.6 nm, very close to the actual Abbe-limit of 12.4 nm, which is the highest resolution achieved from any table-top XUV or X-ray microscope. In addition, 20.5 nm resolution was achieved with only 3 sec of integration time bringing live diffraction imaging and 3D tomography on the nanoscale one step closer to reality. The current resolution is solely limited by the wavelength and the detector size. Thus, table-top nanoscopes with only a few-nm resolutions are in reach and will find applications in many areas of science and technology.Coherent diffractive imaging (CDI) is an imaging technique that provides amplitude and phase information of a nanoscale sample from diffraction patterns recorded in the far field. Since no optics is needed between the sample and the detector, it is scalable to smallest resolutions provided that a high photon flux short wavelength light source with good coherence is used for illumination. Despite huge technological efforts, the resolution of conventional X-ray microscopes is still limited to 12 nm to 20 nm [1][2][3] by the fabrication precision of the employed zone plates. In contrast, coherent diffractive imaging and related techniques demonstrated 7 nm [4] and 5 nm resolution [5] already which can be improved with the availability of a better source. Since the short wavelength light can, in contrast to electron beams, even shine through µm-thick samples exciting possibilities in damage-free 3-dimensional (3D) imaging with unprecedented resolution open up [6]. Furthermore, ultrashort X-ray pulses enable time-resolved movies of the fastest dynamics on the nanoscale [7] being relevant for future electronic, optical and magnetic devices. Unfortunately, the applicability of these imaging techniques in science and technology is limited due to the size, cost and accessibility of the typically desired light sources namely synchrotrons and free-electron lasers [8].The advantages of coherent nanoscale microscopy can only be fully exploited in all areas of science with a compact, reliable and powerful table-top implementation. Thus, laser-driven light sources based on high harmonic generation (HHG) [9,10] are considered as a promising alternative which can be implemented on a Clearly, real-world applications in nanoscience require shorter integration times and the smallest possible resolutions. Once the measurement times for a single high-resolution 2D image has been reduced to seconds, even 3D tomography or ptychographic imaging of large objects [13,14], which requires imaging of hundreds of individual diffraction patterns, get practically feasible with table-top setups. Significantly shorter...

We theoretically study high-harmonic generation (HHG) from transition metal elements Mn and Mn + , using full-dimensional, all-electron, first-principles simulations. The HHG spectra calculated with the time-dependent complete-active-space self-consistent-field (TD-CASSCF) and occupationrestricted multiple-active-space (TD-ORMAS) methods exhibit a prominent peak at ∼ 50 eV, successfully reproducing resonant enhancement observed in previous experiments [R. A. Ganeev et al., Opt. Express 20, 25239 (2012)]. Artificially freezing 3p orbitals in simulations results in its disappearance, which shows the essential role played by 3p electrons in the resonant harmonics (RH). Further transition-resolved analysis unambiguously identifies constructively interfering 3p-3d (m = 0, ±1) giant resonance transitions as the origin of the RH, as also implied by its position in the spectra. Time-frequency analysis indicates that the recolliding electron combines with the parent ion to form the upper state of the transitions. In addition, this study shows that the TD-CASSCF and TD-ORMAS methods can be applied to open-shell atoms with many unpaired inner electrons.

The response of a bulk dielectric to an intense few-cycle laser pulse is not solely determined by the pulse envelope, but also by ultrafast processes occuring during each optical cycle. Here, a method is presented for measuring the retardation of a probe pulse in a strong-field pumped, bulk dielectric with subcycle resolution in the pump–probe delay. Comparisons to model calculations show that the measurement is sensitive to the timing of the electronic Kerr response. When conduction band states are transiently populated at the crests of the laser field, the measurement is also sensitive to the interband dephasing time.

Lensless coherent diffractive imaging usually requires iterative phase-retrieval for recovering the missing phase information. Holographic techniques, such as Fourier-transform holography (FTH) or holography with extended references (HERALDO), directly provide this phase information and thus allow for a direct non-iterative reconstruction of the sample. In this paper, we analyze the effect of detector noise on the reconstruction for FTH and HERALDO with linear and rectangular references. We find that HERALDO is more sensitive to this type of noise than FTH, especially if rectangular references are employed. This excessive noise, caused by the necessary differentiation step(s) during reconstruction in case of HERALDO, additionally depends on the numerical implementation. When considering both shot-noise and detector noise, we find that FTH provides a better signal-to-noise ratio (SNR) than HERALDO if the available photon flux from the light source is low. In contrast, at high photon flux HERALDO provides better SNR and resolution than FTH. Our findings will help in designing optimum holographic imaging experiments particularly in the photon-flux-limited regime where most ultrafast experiments operate.

Charge migration (CM) is a coherent attosecond process that involves the movement of localized holes across a molecule. To determine the relationship between a molecule’s structure and the CM dynamics it exhibits, we perform systematic studies of para-functionalized bromobenzene molecules (X–C6H4–R) using real-time time-dependent density functional theory. We initiate valence-electron dynamics by emulating rapid strong-field ionization leading to a localized hole on the bromine atom. The resulting CM, which takes on the order of 1 fs, occurs via an X localized → C6H4 delocalized → R localized mechanism. Interestingly, the hole contrast on the acceptor functional group increases with increasing electron-donating strength. This trend is well-described by the Hammett σ value of the group, which is a commonly used metric for quantifying the effect of functionalization on the chemical reactivity of benzene derivatives. These results suggest that simple attochemistry principles and a density-based picture can be used to predict and understand CM.