The behavior of a thin-film GeTe crystal induced by intense femtosecond laser pulses ( λ = 0.8 1pt μm) has been studied using a pulsed electron diffractometer. The sample is an annealed 20-nm GeTe film on a copper grid with a carbon coating. It has been found that laser ablation results in the formation of an ultrathin GeTe crystal (assumingly, GeTe monolayer) with a high radiation resistance. Possible reasons for the detected nanosize effect are discussed.

The possibility of amorphization of a thin germanium telluride crystal irradiated by high-power 800-nm femtosecond laser pulses has been investigated. The sample was a 20-nm-thick film of crystalline semiconductor GeTe. An electron diffractometer with a source of short photoelectron pulses was used to study the structural changes. The electron diffraction patterns were analyzed, and the α- and β- phases have been identified in GeTe. It is established that sample ablation occurs in the strong field of femtosecond laser pulses, which is accompanied by a decrease in the crystalline phase thickness to 5–6 nm without any significant amorphization of the sample. A specific feature of the observed process—the absence of light-induced transition of a thin GeTe film from the crystalline to the amorphous state under femtosecond laser irradiation—is noted. Possible causes of the revealed effect are discussed.

Using a compact diffractometer that was equipped with a pulsed electron source synchronized with a femtosecond laser, a series of investigations of laser-stimulated processes in thin-film samples has been performed. It has been revealed that graphene on a copper grid exposed to the action of powerful laser radiation experiences an irreversible structural modification, which is accompanied by the breaking of carbon bonds and formation of new products. Reversible processes of the optical excitation of the crystal lattice in antimony and bismuth thin films have been investigated by ultrafast electron diffraction and the spectrum of coherent optical phonons has been observed.

The feasibility of using direct broad band optical monitoring control in the fabrication of the ultra-steep dichroic filters based on resonant structures is investigated. Using computational manufacturing and deposition experiments, the role of the errors self-compensation effect is clarified by comparing the results of direct broad band optical monitoring and time monitoring. The errors correlation strength of ultra-steep dichroic filter is analyzed and it shows that the correlation calculated by the current model is not strong. The relationship between errors correlation and errors self-compensation effect for the ultra-steep dichroic filter is discussed.

When systematic errors (external radiation, faults in drawing the background curve, too rough model or too strict constraints on the set of determined parameters, etc.) in gas electron diffraction are significant and comparable to random ones, it is necessary to modify the generally accepted statistical formulas used to estimate the errors of the fitted parameters. We present a modified computational procedure accounting for systematic errors in the input data and examples of parameter evaluation for molecules with internal rotation. In all these examples, the confidence intervals for the parameters become narrower.

The model of Regularized Quantum Mechanical Force Field (RQMFF) was applied to the joint treatment of ab initio and experimental vibrational data of the four primary nucleobases using a new algorithm based on the scaling procedure in Cartesian coordinates. The matrix of scaling factors in Cartesian coordinates for the considered molecules includes diagonal elements for all atoms of the molecule and off-diagonal elements for bonded atoms and for some non-bonded atoms (1–3 and some 1–4 interactions). The choice of the model is based on the results of the second-order perturbation analysis of the Fock matrix for uncoupled interactions using the Natural Bond Orbital (NBO) analysis. The scaling factors obtained within this model as a result of solving the inverse problem (regularized Cartesian scale factors) of adenine, cytosine, guanine, and thymine molecules were used to correct the Hessians of the canonical base pairs: adenine–thymine and cytosine–guanine. The proposed procedure is based on the block structure of the scaling matrix for molecular entities with non-covalent interactions, as in the case of DNA base pairs. It allows avoiding introducing internal coordinates (or coordinates of symmetry, local symmetry, etc.) when scaling the force field of a compound of a complex structure with non-covalent H-bonds.

The coherent lattice dynamics in thin crystalline Sb and Bi films has been investigated using ultrafast electron diffraction. The samples were exposed to Ti:sapphire femtosecond laser radiation and probed by ultrashort electron pulses. The registered generation of coherent optical phonons in the crystals corresponded to the A1g and Eg modes and their combinations in Sb, as well as to the manifestation of the A1g mode and its first and second overtones in Bi. Detection of optical phonons with frequencies of up to 9 THz indicated that a temporal resolution at a level of ~100 fs was obtained. An ultrafast electron diffractometer for studying nonlinear laser-induced processes in molecular and cluster beams has been developed based on a femtosecond electron source.

It is shown that the previously proposed geometric approach adequately describes the effect of error correlation based on the results of computational manufacturing experiments with the selected type of optical monitoring. The question of a sufficient number of simulation runs is investigated, and it is shown that a reliable estimate of the correlation coefficient describing the strength of the error correlation effect is obtained with a realistic number of computational manufacturing experiments. To investigate the presence of the error self-compensation effect, the error self-compensation coefficient is introduced. Using sets of correlated error vectors obtained in computational manufacturing experiments, the probability density function of the distributions of this coefficient is calculated. To assess the strength of the error self-compensation effect, the estimate is proposed based on a comparison of the influence of correlated and uncorrelated thickness errors.

The equilibrium structure of the 3,3,6-trimethyl-1,5-diazabicyclo[3.1.0]hexane (TMDABH) molecule was studied for the first time by means of gas-phase electron diffraction (GED) supplemented with quantum chemical calculations. TMDABH exists as a mixture of two conformers of Cs point group symmetry, namely, a chair and a boat. The fractions of these two forms are 74 and 26% respectively, if the reference approximation was obtained at the MP2/aug-cc-PVTZ level, and 81 and 19%, if the reference approximation was generated at the DFT-B3LYP/cc-pVTZ level. The agreement between the theoretical and experimental molecular intensities is characterized by Rf disagreement factors of 5.06 and 6.93%, respectively. Based on the more accurate MP2/aug-cc-PVTZ quantum chemical approximation, the energy difference between the global minimum, which corresponds to the chair conformer of TMDABH, and the local minimum of the boat on the potential energy surface (PES) was found to be 1.39 kcal/mol. Moreover, NMR, IR, and Raman spectroscopic studies were carried out. According to the joint analysis of the data obtained, the most important equilibrium parameters of the chair and boat TMDABH conformers were determined to be as follows (bond lengths in Å, angles in degrees, for boat form in square brackets, Cs symmetry): N1N5 = 1.554(2) [1.520(2)], C2C3 = 1.525(2) [1.539(2)], N1C2C3 = 105.7(14) [108.8(14)], θ = C2-C3-C4/C2-N1-N5-C4 = 37.4(6) [−16.6(6)], φ = N1-C6-N5/C2-N1-N5-C4 = 72.9(3) [73.9(3)]. Comparison of especially NN bond lengths reveals a strong dependence on the bicyclic system conformation.

The paper presents a comparative analysis of three fundamentally different algorithms for solving inverse problems of monitoring the layer thicknesses of optical coatings based on the data of monochromatic measurements of the reflection/transmission coefficients during deposition process. The previously developed geometric approach to the study of the thickness error correlation of deposited coatings is extended to the case of monochromatic measurements. A new parameter called the self-compensation factor was introduced to estimate the effect of error self-compensation. Its role in assessing the prospects for using various algorithms for coating deposition monitoring is shown.

For optical monitoring of layer thickness in the deposition of multilayer optical coatings, a stable method is proposed that completely eliminates the cumulative effect of errors in the thicknesses of deposited layers. The considered monitoring method relies on a nonlocal algorithm for analyzing data measured in the course of coating deposition monitoring. Computer simulation of coating deposition is used to demonstrate the effectiveness of the proposed type of monitoring as compared with other optical monitoring methods.

The paper presents a theoretical study of the correlation of errors in the thickness of layers of multilayer optical coatings produced using monochromatic monitoring of the deposition process. Estimates of the degree of error correlation in layer thicknesses are obtained for various algorithms for determining termination instants for layer depositions. It is shown that the parameter introduced to assess the degree of correlation gives an adequate idea of the error correlation in the case of monochromatic monitoring.

Advances in the development of pulsed lasers provided a further breakthrough in the study of the structural dynamics of nuclei and electrons. As a result of this progress, the use of powerful femtosecond laser pulses, both for exciting a sample and for generating ultrashort (down to femto- and even subfemtosecond) photoelectron bunches synchronized with optical pulses for sensing matter, made it possible to observe the coherent dynamics of nuclei and electrons in samples at the required spatiotemporal scales. The possibility of direct observations of reaction processes is a major breakthrough in chemical physics. The many-particle potential is so complex that the degree of the interaction nonadiabaticity cannot be determined with an accuracy sufficient for predicting reaction paths. How can this information and a new look at the reaction dynamics be used in the future? This question arises in connection with the development of a new conceptual foundation of natural sciences incorporating the convergence of experimental and theoretical tools in studies of systems of any complexity with atomic resolution. In this approach, an ‘atomic–molecular’ movie is obtained by using mutually complementary information extracted from simultaneous studies of ultrafast electron (or X-ray) diffraction, spectroscopy, and the quantum dynamic theory of matter.

On-line optical monitoring of multilayer coating production requires solving inverse identification problems of determining the thicknesses of coating layers. Regardless of the algorithm used to solve inverse problems, the errors in the thicknesses of the deposited layers are correlated by the monitoring procedure. Studying the correlation of thickness errors is important for the production of the most complex optical coatings. We develop a general geometric approach to study this correlation. It is based on a statistical analysis of large numbers of error vectors obtained during computational experiments on optical coating production. The application of the proposed approach is demonstrated using computational manufacturing experiments on the production of a 50-layer filter with four different monitoring strategies. A special coefficient is introduced to evaluate the strength of the error correlation effect. The results obtained confirm that the introduced parameter can be used as a measure of the strength of the correlation effect in practical applications.

A new computational approach is developed to evaluate the strength of the error self-compensation effect in the case of broadband optical monitoring of the multilayer coating deposition process. A new form of estimating the strength of the error self-compensation effect is suggested. Computational experiments simulating the deposition process are used to study the presence of the self-compensation effect and it is shown that the assessment of two parameters characterizing the degree of error correlation and the strength of the self-compensation effect is sufficient from a practical point of view.

The main mathematical results on the data processing in vibrational spectroscopy are presented. The approaches and algorithms proposed for molecular force field calculations have been constructed on a base of regularizing methods for solving nonlinear ill-posed problems and have been implemented in the software package SPECTRUM. These algorithms were used for constructing the regularized ab initio force fields of important biological molecules including the melatonin and Vitamin B6 derivatives.