Spin-dependent effects in atomic processes can be caused by the spin–orbit interaction or/and by the requirement that the wave function of identical electrons is antisymmetric. Such effects are usually neglected in strong-field physics. We show two examples, supported by theoretical results and numerical calculations, in which these effects are important. The first one is based on strong-field ionization of Xe atoms by a bicircular field. The corresponding momentum distribution of spin-polarized electrons emitted in the above-threshold ionization process exhibits wavelength-dependent fast oscillations. For longer wavelengths and small electron emission angle there is a wide photoelectron kinetic energy region in which the spin asymmetry parameter changes continuously from large positive to large negative values. In addition, the emission time of such electrons in high-order above-threshold ionization is determined on the attosecond time scale. The second process considered is high-order above-threshold ionization of excited Li+ ions. We have found that in this case, even in the absence of spin–orbit coupling, the photoelectron momentum distribution strongly depends on the initial spin state. In the singlet state we have characteristic minima, which are caused by the destructive interference of the direct and exchange rescattering amplitudes. Such minima are absent in the triplet state.

ABSTRACT We investigate high-order harmonic generation of non-planar ammonia molecules by a bicircular field, which consists of two coplanar counter-rotating circularly polarised fields of frequencies ω and 2ω. This field possesses dynamical symmetries, which can be used together with the symmetry of the molecular Hamiltonian to obtain the selection rules for harmonic emission. We show analytically and confirm by numerical calculations that circularly polarised harmonics of order n = 3q ± 1, with q integer, as well as linearly polarised harmonics of order n = 3q are emitted. The presence of well-separated both linearly and circularly polarised harmonics in the same spectrum is unique to non-planar molecules.

The exact time-evolution operator of an atom in the presence of a strong laser field is expressed using the phase-space path integral. Presenting this result in the form of a perturbative expansion in the effective interaction of the electron with the rest of the atom enables straightforward derivation of the well-known strong-field approximation and its higher-order corrections. Alternatively, one can use this exact result to obtain a semiclassical approximation by expansion in powers of small fluctuations around the classical trajectories. We present a derivation of such a semiclassical approximation. The obtained result for the momentum-space matrix element of the total time-evolution operator can be useful for studying various processes in strong-field physics. Using the example of above-threshold ionization, it is shown how this approximation can be applied to laser-induced processes. More attention is devoted to the laser-assisted scattering. Using the example of few-cycle laser-pulse-assisted electron-atom potential scattering, we show similarities and differences between the semiclassical and the strong-field approximations. For low energies, the semiclassical scattering cross section is modified and there are trajectories along which the electron is temporarily captured by the atomic potential. Applying stationary-phase method to the integral over the scattering time, we clearly identified relevant semiclassical electron trajectories.

The strong-field-approximation theory of high-order above-threshold ionization of atoms is generalized to include the electron spin. The obtained rescattering amplitude consists of a direct and exchange part. On the examples of excited He atoms as well as ${\mathrm{Li}}^{+}$ and ${\mathrm{Be}}^{++}$ ions, it is shown that the interference of these two amplitudes leads to an observable difference between the photoelectron momentum distributions corresponding to different initial spin states: Pronounced minima appear for singlet states, which are absent for triplet states.

Electron-ion radiative recombination assisted by a bichromatic (two-component) elliptically polarized laser field is analyzed in the frame of the $S\text{-matrix}$ theory. The second Born approximation is applied in the expansion of the $S\text{-matrix}$ element where the first term in the expansion corresponds to the direct recombination of electrons with ionic targets, while the second term corresponds to the recombination preceded by an electron-ion scattering. The latter process is possible in the presence of a laser field. If the electron scatters on an ionic target, it may be subsequently driven back by the laser field and recombine with the same ion. The photon emitted in this process may have a high energy. We have studied the dependence of the energy spectrum on various laser-field and incident electron parameters. The energy spectra obtained show plateaulike structures with abrupt cutoffs. These cutoffs are explained by a classical analysis.

Time evolution of the bound state of a molecular hydrogen cation in an intense, linearly polarized laser field is investigated by solving the full three-dimensional time-dependent Schrödinger equation. Our method is based on the Born-Oppenheimer and dipole approximations, and the wave function is expanded in finite series using B-spline functions and spherical harmonics in prolate spheroidal coordinates. After solving the stationary Schrödinger equation, the initial state is propagated under the influence of the laser field employing the Crank-Nicolson propagator. Using this method we calculate and present high-harmonic photon spectra and above-threshold ionization angle-resolved electron spectra.

Above-threshold ionization (ATI) of atoms by a strong bicircular laser field is investigated using the strong-field approximation and the quantum-orbit theory. The bicircular field consists of two coplanar counterrotating circularly polarized fields with a frequency ratio of 2:1. The velocity map of the angle-resolved ATI spectra, both for direct and rescattered electrons, reflects the shape of a parametric plot of the bicircular field and its symmetries. It is shown that the main characteristics of the ATI spectra can be explained using only a few quantum orbits having short travel times. We also analyze a recently discovered [Phys. Rev. A 93, 052402(R) (2016)] bicircular-field-induced spin asymmetry of the ATI electrons and show that the momentum dependence of the spin-asymmetry parameter is stronger for longer wavelengths.

We present a theory of high-order harmonic generation by arbitrary polyatomic molecules based on the molecular strong-field approximation (MSFA) in the framework of the S-matrix theory. A polyatomic molecule is modeled by an (N + 1)-particle system, which consists of N heavy atomic (ionic) centers and an electron. We derived various versions (with or without the dressing of the initial and/or final molecular state) of the MSFA. The general expression for the T-matrix element takes a simple form for neutral polyatomic molecules. We show the existence of the interference minima in the harmonic spectrum and explain these minima as a multiple-slit type of interference. This is illustrated by numerical examples for the nitrous oxide (N2O) molecule exposed to strong linearly polarized laser field.

The First Mediterranean Seminar on Science Writing, Editing & Publishing (SWEP 2016) was held in Sarajevo, Bosnia & Herzegovina from 2nd to 3rd December 2016. It was organized by Academy of Medical Sciences of Bosnia and Herzegovina, running concurrent sessions as part of its Annual Meeting titled “ “Days of AMNuBiH - Theory and Practice in Science Communication and Scientometrics”. Hotel Bosnia in the city centre was the chosen venue. On the first day, nineteen presentations on various issues of science writing and publication ethics were delivered by speakers from Croatia, Serbia, Macedonia, Albania, Bosnia & Herzegovina and the UK (Asim Kurjak, Milivoj Boranić, Doncho Donev, Osman Sinanović, Miro Jakovljević, Enver Zerem, Dejan Milošević, Silva Dobrić, Srećko Gajović, Izet Mašić, Armen Yuri Gasparyan, Šekib Sokolović, Nermin Salkić, Selma Uzunović, Admir Kurtčehajić, Edin Begić and Floreta Kurti). Each presentation had a take-home message for novice and seasoned authors, encountering numerous problems in non-Anglophone research environment. Lecturers, who were internationally recognized editors of regional journals, generously shared their experience of adhering to the best ethical guidance. Elegant presentations by Srećko Gajović (Editor-in-Chief of the Croatian Medical Journal) and Armen Yuri Gasparyan (past Chief Editor of the European Science Editing) showcased their accomplishments that strengthened ties between authors from all over the world. Gasparyan reflected on educational resources of editorial associations, such as the International Committee of Medical Journal Editors (ICMJE) and the Committee on Publication Ethics (COPE), and called not just to declare the adherence to, but also to enforce their ethical guidance in daily practice. Editors of Medical Archives, Croatian Medica Journal, Vojnosanitetski Pregled, Psychiatria Danubina, Acta Informatica Medica, Materia Socio-Medica, The Donald School Journal of Ultrasound in Obstretics and Gynecology, Acta Medica Saliniana and Medicinski Glasnik presented their editorial strategies aimed at attracting best authors and resolving problems with authorship, conflicts of interest, and plagiarism. Topical education on science writing and editing was considered as an inseparable part of continuing professional development in biomedicine. Armen Yuri Gasparyan (UK) was offered an opportunity to interact with more than 70 participants, attending the SWEP 2016 on the second day. The lecturer talked about author contributions, disclosures of conflicts of interests, plagiarism of ideas and words, research performance and impact indicators, and targeting ethical journals. Topics were presented in a way to help non-Anglophone authors, reviewers and editors avoid common ethical problems. Dr Gasparyan stressed the importance of regularly arranging such meetings across Balkan and Mediterranean countries to eradicate plagiarism and other forms research misconduct. The organizers of the SWEP 2016 awarded selected keynote speakers with certificates of lifetime achievement in journal editing, and decided to run the Seminar annually with support of Balkan and Mediterranean editors and publishers. The SWEP 2016 marked a turning point in the process of regional developments since all attending editors opted for nurturing enthusiasm of the organizers and launching the Mediterranean Association of Science Editors and Publishers (MASEP). The Seminar was a great success with its impressive scientific and social activities. It attracted more than 100 students, researchers, editors, and publishers from Bosnia & Herzegovina and neighbouring countries. Proceedings, in the form of short reports, were published in Acta Informatica Medica and archived in PubMed Central. New friendships were forged between regional experts in editing and young specialists during those unforgettable two days of intensive discussions and informal interactions (a-y).

Изет Машич1, 2,*, Един Бегич3, 4, Дончо M. Донев5, Сречко Гайович6, Армен Ю. Гаспарян7, Миро Яковлевич8, Деян Б. Милошевич9, 10, Осман Синанович2, 11, Шекиб Соколович12, Сельма Узунович13, Энвер Зерем14, 15 1Медицинский факультет, Университет Сараево, Сараево, Босния и Герцеговина 2Академия медицинских наук Боснии и Герцеговины, Сараево, Босния и Герцеговина; https://orcid.org/0000-00029080-5456 3Медицинский факультет, Школа науки и технологий Сараево, Сараево, Босния и Герцеговина 4Центр охраны здоровья, Маглай, Босния и Герцеговина; http://orcid. org/0000-0001-6842-262X 5Институт социальной медицины, медицинский факультет, Университет им. св. Кирилла и Мефодия в Скопье, Скопье, Республика Македония; https://orcid.org/0000-0002-5237-443X 6Хорватский институт исследований мозга, Школа медицины при Загребском университете, Загреб, Хорватия; http://orcid.org/0000-0001-86685239 7 Отделение ревматологии и отдел исследований и развития, Дадли группа Благотворительного фонда Системы общественного здравоохранения (Образовательный фонд Университета Бирмингема, Великобритания), Расселовский Ходл Госпиталь, Дадли, Уэст-Мидлендс, Великобритания; https://orcid.org/0000-0001-8749-6018 a.gasparyan@gmail.com 8Отделение психиатрии, Центральная университетская клиника Загреба, Загреб, Хорватия 9Факультет естественных наук, Университет Сараево, Сараево, Босния и Герцеговина 10Aкадемия наук и художеств Боснии и Герцеговины, Сараево, Босния и Герцеговина; http://orcid.org/0000-00015060-3318 11Отделение неврологии, Университетский клиническй центр Тузлы, медицинский факультет, Университет Тузлы, Тузла, Босния и Герцеговина; http://orcid.org/0000-0001-8957-7284 12Институт болезней сердца, Университетский клинический центр Сараево, Сараево, Босния и Герцеговина; http://orcid.org/0000-00016321-4186 13Отделение лабораторной диагностики, Институт общественного здоровья и продовольственной безопасности, Зеница, Босния и Герцеговина; http:// www.orcid.org/0000-00031852-1572 14Отделение медицинских наук, Академия наук и художеств, Сараево, Босния и Герцеговина 15Отделение гастроэнтерологии и гепатологии, Университетский клинический центр Тузлы, Тузла, Босния и Герцеговина; http://orcid. org/0000-0001-6906-3630

Using the quantum–orbit formalism we consider the influence of the backward-scattering quantum orbits on the low-energy above-threshold ionization spectra. It is shown that the corresponding ionization rate exhibits sharp peaks for electron energies ≲ 0.1 U P ( U P is the electron ponderomotive energy) at the same places where the forward-scattering-induced low-energy structures appear. The corresponding incident rescattering electron velocities are very small. Semiclassical expressions for the positions of these peaks as functions of U P and the ionization potential are derived.

A theory of above-threshold ionization of atoms by a strong laser field is formulated. Two versions of the strong-field approximation (SFA) are considered, the direct SFA and the improved SFA, which do not and do, respectively, take into account rescattering of the freed electron off the parent ion. The atomic bound state is included in two different ways: as an expansion in terms of Slater-type orbitals or as an asymptotic wave function. Even though we are using the single-active-electron approximation, multielectron effects are taken into account in two ways: by a proper choice of the ground state and by an adequate definition of the ionization rate. For the case of the asymptotic bound-state wave functions, using the saddle-point method, a simple expression for the $T$-matrix element is derived for both the direct and the improved SFA. The theory is applied to ionization by a bicircular field, which consists of two coplanar counterrotating circularly polarized components with frequencies that are integer multiples of a fundamental frequency $\ensuremath{\omega}$. Special emphasis is on the $\ensuremath{\omega}\text{\ensuremath{-}}2\ensuremath{\omega}$ case. In this case, the threefold rotational symmetry of the field carries over to the velocity map of the liberated electrons, for both the direct and the improved SFA. The results obtained are analyzed in detail using the quantum-orbit formalism, which gives good physical insight into the above-threshold ionization process. For this purpose, a specific classification of the saddle-point solutions is introduced for both the backward-scattered and the forward-scattered electrons. The high-energy backward-scattering quantum orbits are similar to those discovered for high-order harmonic generation. The short forward-scattering quantum orbits for a bicircular field are similar to those of a linearly polarized field. The conclusion is that these orbits are universal, i.e., they do not depend much on the shape of the laser field.