In this contribution, we discuss the features of design and polarimetric inspection of terahertz achromatic waveplates. The design of the crystalline quartz half-wave plate was performed taking into account the ellipticity and the introduced phase difference between the orthogonal components of the output radiation polarization vector. The designed waveplate are relatively thin, work equally efficiently in the frequency range from 0.4 to 1.4 THz, and, most importantly, are cheap to manufacture. The modification of the experimental terahertz time-domain spectroscopy polarimetric setup involving direct waveform detection is proposed. The proposed polarimetry THz time-domain spectrometer with electro-optic detection shows parasitical signals absence and easier measurement procedure.
In this paper a nanostructure for DNA detection was proposed. The aim of the work is a theoretical analysis of the
construction. The optimal dimensions of the nanostructure were determined. The characteristics of the model were
obtained. It was revealed that the resonant wavelength changes by more than 100 nm, which can be detected even
without using any instruments.
In this paper, we present the results of the propagational dynamics of vortex beams array in the scope of their possible applications for non-contact robust and precision optical surface profilometry with nanoscale resolution. The result of coaxial superposition of the reference array with the object array of oppositely charged vortex beams represents a dynamically changing intensity distribution. The nature of this changes, namely, rotational effects of "two-petal” beams, allows to determine directly the phase delay between the beams which is introduced by the test object. We have analyzed the process of creating an array of singular beams and the features of experimental setup for detecting of reflecting and transmitting objects.
In this article, we analyze the possibilities of non-contact confinement of micron-sized absorbing particles using optical traps based on a spatially structured beam. The proposed method utilizes multi-beam interference with controllable parameters including tilt angles, waists and a number of superposed beams. The effectiveness of trapping and its selectivity to variable masses and shapes of particles is determined by axial symmetry of spatial intensity distribution at the trapping area. In addition to implementing non-contact trapping, optical visualization was performed with axial digital holographic microscopy in-situ. This method contributes to the accurate localization of studied specimens inside the cuvette.
In this contribution, we investigate the features of the two-beam interference of a set of wave trains, in which one of the beams contains an orbital angular momentum caused by the presence of inline topologically charged vortices in each spectral component. The infrared pump beam that generates terahertz radiation is first doubled in Mach-Zehnder interferometer with a specific time delay value to form the wave train with quasidiscrete temporal spectrum. Then, the two delayed terahertz pulses are split into two arms. One of the arms contains a delay line and geometric phase shaping elements for broadband uniformly topologically charged beam formation. The resulting structures are combined with a beamsplitter and detected with a terahertz holographic system upon their propagation. We analyze the features of the resulting spatio-frequency structures and discuss the possibility to implement the information encoding without spectral decomposition.
We investigate an approach to short and medium-range wireless communications based on the use of terahertz beams possessing an orbital angular momentum (OAM) that allows for noise-resistant broadband carrier. A the- oretical model of the proposed beams generation is developed and numerical predictions are given for propagation and visualization of complex-structured THz beams, including ones carrying a unit topological charge on a large number of spectral components of broadband terahertz radiation. The assessment method which in our case is terahertz pulse time-domain holography allows for analyzing spatio-temporal and spatio-spectral evolution of arbitrary shaped THz wave trains during their propagation in free space and interaction with obstacles.
Practical application of optical vortex in a method of three-dimensional profilometry with nanoscale resolution was considered. It was shown that phase analysis of coherent light beam carrying axial optical vortex allow to retrieve information about sample surface relief. High spatial resolution caused by vortex helical phase sensitivity to disturbances in wave front after reflection or spreading through studying sample, which can be optically transparent or have a reflecting surface. This method applicable for non-destructive testing of live cells and biological tissues in real-time regime with exceeding optical diffraction limit. Computer processing of vortex interferograms allow to achieve a vertical resolution down to 1.75 nm. Specially designed optical scheme reduces an environment influence, in particular, vibration, misalignment of test sample and its local anisotropy and provides the possibility of investigating surfaces of large linear dimensions. The prospective tasks of automated systems creation for monitoring of surface quality were proposed, in particular those that will could be developed with methods based on singular optics and phase singularities.
We have experimentally analyzed the behavior of Gaussian beam with elliptical cross-section passed through the uniaxial crystal in direction near perpendicular to the crystal’s optical axis. The projection of total angular momentum flux on the axis consists of projection of two components: the spin (SAM) and orbital (OAM) angular momentum. We have revealed that in anisotropic media the SAM describes the polarization state of the beam cross-section and OAM reflects the shape and topological charge of the singularity at ordinary and extraordinary beams. The sum of projections SAM and OAM remains constant. The oscillations of spin-orbital angular momentum projection were described experimentally during the crystal was rotated around z axis with small beam inclination. The low changes in the extraordinary beam cross section and their correlation with polarization state allow us to analyze the form of angular momentum conversion and possibility for generation of polarizing singularities. The feasibility of optical vortex generation in the system of uniaxial crystal with tilted Gaussian beam was theoretically and experimentally investigated.
In this paper we report on the progress in building the superresolution microscope using optical vortices. The outline of the general idea is presented. Some of the specific problems are discussed in more details. Specifically, the scanning
method by vortex lens movement is discussed.
We have experimentally analyzed the topological reactions occurred in the elliptic vortex-beam transmitting
orthogonally to the optical axis of the SiO2 crystal. We have revealed that the oscillations of the polarization state when
propagating the beam are accompanied by reconstruction of the polarization singularities at the beam cross-section that, in
turn, entails the reconstruction of the wavefront in each circularly polarized beam component. Both synchronic oscillations of
the spin angular momentum and the sign of the vortex topological charge are expressing in a field structure as birth and
annihilation of topological dipoles. Also periodical conversion of the vortex ellipticity along the crystal length z and huge
splash of spin angular momentum were analysed. The run of the dislocation reactions in the beam component results in
converting the sign of the topological charge in the centered optical vortex, the distance of the vortex conversion being about
0.05 of the wavelength.
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