Chiral discrimination in optical trapping and manipulation

When circularly polarized light interacts with chiral molecules or nanoscale particles powerful symmetry principles determine the possibility of achieving chiral discrimination, and the detailed form of electrodynamic mechanisms dictate the types of interaction that can be involved. The optical trapping of molecules and nanoscale particles can be described in terms of a forward-Rayleigh scattering mechanism, with trapping forces being dependent on the positioning within the commonly non-uniform intensity beam profile. In such a scheme, nanoparticles are commonly attracted to local potential energy minima, ordinarily towards the centre of the beam. For achiral particles the pertinent material response property usually entails an electronic polarizability involving transition electric dipole moments. However, in the case of chiral molecules, additional effects arise through the engagement of magnetic counterpart transition dipoles. It emerges that, when circularly polarized light is used for the trapping, a discriminatory response can be identified between left- and right-handed polarizations. Developing a quantum framework to accurately describe this phenomenon, with a tensor formulation to correctly represent the relevant molecular properties, the theory leads to exact analytical expressions for the associated energy landscape contributions. Specific results are identified for liquids and solutions, both for isotropic media and also where partial alignment arises due to a static electric field. The paper concludes with a pragmatic analysis of the scope for achieving enantiomer separation by such methods

Повышение эффективности лазерного управляемого термораскалывания силикатных стекол с использованием метода фотоупругости

A method for monitoring the development of a separating crack in the process of laser-controlled thermal splitting of silicate glasses is proposed. This method is based on the polarization-optical method (photoelasticity method). The method was developed on the basis of numerical modeling and experimental studies of the process using a polarized light source and a video camera with an analyzer. During the cutting process, a source of polarized light creates a stream, which, passing through silicate glass, enters a video camera with an analyzer. Analysis of the parameters of polarized light in the area of material processing allows us to drawa conclusion about the stable development or absence of the formation of a separating microcrack. Based on the information obtained, it is necessary to dynamically make corrections to the technological parameters of the laser thermal splitting process for separating silicate glasses to maintain the value of thermoelastic stresses necessary for the formation of a microcrack, or transmit a command to interrupt the process.Предложен метод контроля развития разделяющей трещины в процессе лазерного управляемого термораскалывания силикатных стекол, в основе которого лежит поляризационно-оптический метод (метод фотоупругости). Метод разработан на базе численного моделирования и экспериментальных исследований процесса с использованием источника поляризованного света и видеокамеры с анализатором. Во время процесса резки источник поляризованного света создает поток, который, проходя через силикатное стекло, попадает в видеокамеру с анализатором. Анализ параметров поляризованного света в области обработки материала позволяет сделать вывод об устойчивом развитии или отсутствии образования разделяющей микротрещины. По полученной информации необходимо динамически вносить коррекцию в технологические параметры процесса лазерного термораскалывания разделения силикатных стекол для поддержания значения термоупругих напряжений, необходимых для формирования микротрещины, либо передавать команду прерывания процесса