Table of contents

The ability to resolve the complete electric field of laser pulses from terahertz to mid-infrared spectral ranges has enriched time-domain spectroscopy for decades. Field-resolved measurements in this range have been performed routinely in ambient air by various techniques like electro-optic sampling, photoconductive switching, field-induced second harmonic generation, and time stretch photonics. On the contrary, resolving the electric field of light at the near-infrared spectral range has been limited to attosecond streaking and other techniques that require operation in vacuum. Recent advances are circumventing these shortcomings and extending the direct, ambient air field detection of light to petahertz frequencies. In the first part of this letter, recent field-resolved techniques are reviewed. In the second part, different approaches for temporal scanning are discussed, as the temporal resolution of the time-domain methods is prone to temporal jitter. The review concludes by discussing technological obstacles and emerging applications of such advancements.

We present a well-tailored sequence of two Gaussian-pulsed drives that achieves perfect population transfer in stimulated Raman adiabatic passage. We give a theoretical analysis of the optimal truncation and relative placement of the Stokes and pump pulses. Further, we obtain the power and the duration of the protocol for a given pulse width. Importantly, the duration of the protocol required to attain a desired value of fidelity depends only logarithmically on the infidelity. Subject to optimal truncation of the drives and with reference to the point of fastest transfer, we obtain a new adiabaticity criteria, which is remarkably simple and effective.

Photons are the elementary quantum excitations of the electromagnetic field. Quantization is usually constructed on the basis of an expansion in eigenmodes, in the form of plane waves. Since they form a basis, other electromagnetic configurations can be constructed by linear combinations. In this presentation we discuss a formulation constructed in the general formalism of bosonic Fock space, in which the quantum excitation can be constructed directly on localized pulses of arbitrary shape. Although the two formulations are essentially equivalent, the direct formulation in terms of pulses has some conceptual and practical advantages, which we illustrate with some examples. The first one is the passage of a single photon pulse through a beam splitter. The analysis of this formulation in terms of pulses in Fock space shows that there is no need to introduce 'vacuum fluctuations entering through the unused port', as is often done in the literature. Another example is the Hong–Ou–Mandel effect. It is described as a time dependent process in the Schrödinger representation in Fock space. The analysis shows explicitly how the two essential ingredients of the Hong–Ou–Mandel effect are the same shape of the pulses and the bosonic nature of photons. This formulation shows that all the phenomena involving linear quantum optical devices can be described and calculated on the basis of the time dependent solution of the corresponding classical Maxwell's equations for pulses, from which the quantum dynamics in Fock space can be immediately constructed.

A multichannel single center (MCSC) method for the theoretical description of the electron continuum spectrum in molecules is reported. The method includes coupling between different continuum channels via electron correlations and describes, thereby, photoelectron continuum in the Tamm–Dancoff (configuration interaction singles) approximation. Basic equations of the non-iterative one-channel single center (SC) method and their extension to the MCSC method are presented, and an efficient scheme for their numerical solution is outlined. The method is tested on known illustrative examples of the Ar 3s-, HCl 4σ- and N₂ 1σ-photoionization processes, where inter-channel coupling plays a very important role. Unlike our previous SC studies, the present MCSC method can be reliably applied to photoionization of outer and valence molecular orbitals, where inter-channel correlations in the continuum might be relevant.

Aims: tungsten has been chosen for use as a plasma facing component in the divertor for the ITER experiment, and is currently being used on existing tokamaks such as JET. W⁺ plays an integral role in assessing the impurity influx from plasma facing component of tokamaks and subsequent redeposition. Together with previously calculated a neutral tungsten electron-impact dataset this study allows us to determine neighbouring spectral lines in the same wavelength window of the spectrometer, and detect if there is strong blending of overlapping lines between these two ion stages as well as providing ionisation per photon ratios for both species. The new data is to be used for tungsten erosion/redeposition diagnostics. Methods: a significantly modified version of the GRASP0 atomic structure code in conjunction with DARC (Dirac Atomic R-matrix Code) are used to calculate the Einstein A coefficients and collisional rates used to generate a synthetic W II spectrum. The W II spectrum is compared against tungsten spectral emission experiments. Results: this study is used to model the spectrum of W ii, providing the predictive capability of identifying spectral lines from recent experiments. These results provide an integral part of impurity influx and redeposition determination, as the ionisation rates may be used to calculate S/XB ratios.

The ionization dynamics of aligned N₂ molecules are studied in strong elliptical laser fields experimentally and theoretically. The alignment-dependent photoelectron momentum distribution of N₂ is measured for highlighting the molecular structure contribution by comparing to that of Ar measured synchronously. Our results show that the ionization of N₂ depends strongly on the alignment of molecules, relative to the main axis of the polarization ellipse of the laser. In particular, the most-probable electron-emission angle which is often used in attosecond measurement changes remarkably when changing the relative angle between the molecular axis and the major axis of laser fields. The alignment-dependent rotation angles have been well reproduced by our theoretical calculations. We show that the interplay between molecular structure and the laser fields plays an important role in the rotation angles based on the strong-field approximation analysis and this interaction also influences remarkably on the photoelectron angle distribution of aligned N₂.

We report the experimental generalized oscillator strengths (GOSs) for transitions from the ground state $\tilde{X}{}^{1}A_{1}^{\prime }$ to the Rydberg states $\tilde{B}{}^{1}E^{\prime \prime }$, ${\tilde{C}}^{\prime }{}^{1}A_{1}^{\prime }$, $\tilde{D}{}^{1}E^{\prime }+{\tilde{D}}^{{\prime\prime}}{}^{1}A_{2}^{\prime \prime }$, $\tilde{E}{}^{1}E^{\prime }({v}_{2}^{\prime }=0-7)+(\tilde{F}{}^{1}E^{\prime }+\tilde{G}{}^{1}A_{2}^{\prime \prime })({v}_{2}^{\prime }=0-4)$ and an 'undefined' state $\tilde{U}({v}_{2}^{\prime }=0-4)$ in ammonia. The experiment was performed using an angle-resolved electron energy loss spectrometer operated at an incident energy of 1500 eV and an energy resolution of about 80 meV. The experimental observation confirms the recent theoretically predicted appreciable vibrational effects on the GOS for the transition $\tilde{B}{}^{1}E^{\prime \prime }{\leftarrow}\tilde{X}{}^{1}A_{1}^{\prime }$ (2021 J. Phys. B: At. Mol. Opt. Phys. 54 135202). The measured GOS data are fitted with the Lassettre formula to determine the corresponding optical oscillator strengths for dipole-allowed transitions. Furthermore, the fitted curves enable the integrations of GOSs over the momentum transfer squares to obtain the Born excitation cross sections. The integral cross sections are scaled to an accurate scale by using the BE-scaling method. The data in this work can supplement the molecular database and deepen our understanding of the scattering mechanism.

In this paper we investigate the self-reference interferometry of optical vortices using a Michelson interferometer. It is found that the detection of topological charge (TC) for optical vortices is constrained by some physical conditions. We present these conditions through theoretical analyses, numerical simulation and experimental results. The maximal detectable TCs are different for different parameters, which is helpful for the measurement of TC in practical applications. Within the range allowed by the constrained conditions, we also study the detection of TC using the interference pattern of a two-way optical vortex, by changing the inclined angle of one mirror of the Michelson interferometer.

A new theoretical scheme for two-dimensional (2D) electromagnetically induced grating (EIG) is proposed in a three-level Ξ-type atomic system. The system is driven by a weak probe field and two position-dependent coupling fields—a 2D standing-wave field and a vortex field. Due to lopsided spatial modulation of the vortex Laguerre–Gaussian field, the weak probe light could be diffracted into different domains and asymmetric 2D EIG is formed. The result shows that the diffraction patterns and efficiency could be effectively modulated by the azimuthal parameter of the vortex field. Also, the system parameters such as the probe field detuning, the intensity of the vortex field, and the interaction length could be used to regulate the diffraction properties of the 2D EIG effectively. The scheme of asymmetric 2D EIG may have some potential application in all-optical information processing and the design of quantum devices.

In this comment, it is shown that the vibrational energies of the X¹Σ⁺ state of the RbH molecule via improved generalized Pöschl–Teller potential reported by Eyube et al (2021 J. Phys. B: At. Mol. Opt. Phys.54 155102) are calculated incorrectly. Accurate calculations are given in the present study.