An alternative strategy to increase mass transfer entails geometry optimization of the extraction systems including design of solid-phase microextraction (SPME) probes. In this work, a computational model was employed to elucidate practical aspects such as efficiency and kinetics of extraction by employing several new geometries. Extraction of a model analyte at static conditions with the configurations, such as thin-film, fiber, coated tip, and nanoparticles, was numerically simulated to obtain an in-depth understanding of the advantages and limitations of each geometry in microextraction and exhaustive modes. The attained results associated with the equilibration time dependency on shape were in good agreement with previously reported experimental observations. They demonstrate that the mass-transfer is highly dependent on the size and shape of the coatings and increases with a decrease in size of the devices particularly rapidly below 10 μm caused by radial diffusion effect. Nevertheless, extractions performed using octadecyl-functionalized magnetic nanoparticles demonstrated that higher enrichment factors are achievable with the use of a fewer number of particles in comparison to factors achieved via exhaustive extraction, where a larger number of particles must be employed, confirming theoretical predictions. The conclusions reached are valid for any extraction method. The results obtained herein are very useful toward the design and optimization of future extraction technologies and approaches.

ABSTRACT Quantum-orbit theory of high-order harmonic generation (HHG) by bicircular laser field is presented. HHG is a strong laser-field-induced process in which the energy absorbed from the laser field is emitted in the form of a high-energy photon. This process can be described using the strong-field approximation and its approximation – the quantum-orbit theory. We develop a classification of quantum orbits for HHG by bicircular field which consists of two coplanar counter-rotating circularly polarized field of frequencies and , where r and s are integers and ω is a fundamental frequency. Analysis of the contributions of particular quantum orbits to high-harmonic intensity enables a better understanding of the HHG process. The cases of the ω– and ω– bicircular fields and of the atoms having the s and the p ground state are analysed in detail. Particular attention is devoted to the influence of the ratio of the intensities and of the bicircular field components. For inert gases having the p ground state the asymmetry in the emission of the left- and right-circularly polarized harmonics can be large. This is explained comparing the partial harmonic intensities for HHG from the ground state having the magnetic quantum number m=+1 and m=−1 and analysing the contributions of particular quantum orbits and the corresponding electron trajectories and velocities. The contribution of the shortest quantum orbit is dominant. It was found that the electron velocity at the ionization time, which still allows the return of the electron to the parent ion, determines the height of the high-energy HHG plateau. For this velocity is large which, in the case of the p ground state, leads to a large helicity asymmetry parameter. On the other hand, for this velocity is small and the intensity of the high-energy plateau harmonics is high.