Ternary logic in the optical controlled-SWAP gate based on Laguerre-Gaussian modes of light.

The need set by a computational industry to increase processing power, while simultaneously reducing the energy consumption of data centers, became a challenge for modern computational systems. In this work, we propose an optical communication solution, that could serve as a building block for future computing systems, due to its versatility. The solution arises from Landauer's principle and utilizes reversible logic, manifested as an optical logical gate with structured light, here represented as Laguerre-Gaussian modes. We introduced a phase-shift-based encoding technique and incorporated multi-valued logic in the form of a ternary numeral system to determine the similarity between two images through the free space communication protocol.

Vortex-antivortex pair control in quadrupole Gaussian beams.

A multi-vortex system nested in a Gaussian beam forms complex paths when it propagates in a free space. We consider a configuration of vortex quadrupole and present a systematic way to control the creation and annihilation of vortex pairs using only one parameter. It is shown that three classes of quadrupole vortex beams can be identified by the number of vortex pairs created or annihilated. The beam symmetry, asymptotic behavior, and stability are analyzed. The main theoretical results are verified experimentally.

Optical vortex tracking algorithm based on the Laguerre-Gaussian transform.

Optical vortices are stable phase singularities, revealing a zero-point in the intensity distribution. The localization of this singular point is of significant importance for any application that relies on vortices and their behavior. However, there is still a need for an adaptable, fast, and precise method of singular point localization. Here we show, that the Laguerre-Gaussian transform method can meet those criteria. We compared the performance of this method with two other tracking methods (phase retrieval and weighted centroid) in various conditions. We found out that not only Laguerre-Gaussian transform offers high accuracy, but also does not lose its advantages in the low-contrast regime. The versatility of this algorithm is examined in the optical vortex aberrometry, where we sense two artificially introduced aberrations.

Vortex beam as a positioning tool.

Remote positioning by precise measurements of lateral displacements of laser beams at large distances is inevitably disturbed by the influence of atmospheric turbulences. Here we propose the use of optical vortices, which exhibit lower transversal variations at an experimentally validated range of 100 meters. We show the higher precision of the localization of vortex points as compared with standard centroid-based assessment of Gaussian beams. Numerical simulations and experimental measurements show further improvements by averaging of the positions of up to four secondary vortices forming a stable constellation when higher values of the topological charges are used.

Quantifying the quality of optical vortices by evaluating their intensity distributions.

Optical vortices are widely used in optics and photonics, impacting the measurements and conclusions derived from their use. Thus, it is crucial to evaluate optical vortices efficiently. This work aims to establish metrics for evaluating optical vortex quality to support the implementation procedure and, hence, provide a tool supporting research purposes and technological developments. We propose to assess vortex quality using the following intensity parameters: eccentricity, cross-sectional peak-to-valley, cross-sectional peak difference, and the doughnut ratio. This methodology provides a low-cost, robust, and quantitative approach to evaluating optical vortices for each specific optical technology.

Broadband chromatic dispersion measurements in higher-order modes selectively excited in optical fibers using a spatial light modulator.

We propose an improvement of the interferometric method used up to now to measure the chromatic dispersion in single mode optical fibers, which enables dispersion measurements in higher-order modes over a wide spectral range. To selectively excite a specific mode, a spatial light modulator was used in the reflective configuration to generate an appropriate phase distribution across an input supercontinuum beam. We demonstrate the feasibility of the proposed approach using chromatic dispersion measurements of the six lowest order spatial modes supported by an optical fiber in the spectral range from 450 to 1600 nm. Moreover, we present the results of numerical simulations that confirm sufficient selectivity of higher-order mode excitation.

Optical vortex torque measured with optically trapped microbarbells.

Optical vortex beams carry orbital angular momentum and thus exert torque on illuminated objects. A dielectric microtool-a microbarbell-is used in two-laser optical tweezers to measure the torque of a focused optical vortex. The tool was either freely rotating due to the applied torque or set into oscillations by the counteracting force. Four different trapping configurations provided different ways of sensing the torque and gave consistent results. The value of torque was determined by confronting the experimental results with numerical and analytical models.

Profound Nanoscale Structural and Biomechanical Changes in DNA Helix upon Treatment with Anthracycline Drugs.

In our study, we describe the outcomes of the intercalation of different anthracycline antibiotics in double-stranded DNA at the nanoscale and single molecule level. Atomic force microscopy analysis revealed that intercalation results in significant elongation and thinning of dsDNA molecules. Additionally, using optical tweezers, we have shown that intercalation decreases the stiffness of DNA molecules, that results in greater susceptibility of dsDNA to break. Using DNA molecules with different GC/AT ratios, we checked whether anthracycline antibiotics show preference for GC-rich or AT-rich DNA fragments. We found that elongation, decrease in height and decrease in stiffness of dsDNA molecules was highest in GC-rich dsDNA, suggesting the preference of anthracycline antibiotics for GC pairs and GC-rich regions of DNA. This is important because such regions of genomes are enriched in DNA regulatory elements. By using three different anthracycline antibiotics, namely doxorubicin (DOX), epirubicin (EPI) and daunorubicin (DAU), we could compare their detrimental effects on DNA. Despite their analogical structure, anthracyclines differ in their effects on DNA molecules and GC-rich region preference. DOX had the strongest overall effect on the DNA topology, causing the largest elongation and decrease in height. On the other hand, EPI has the lowest preference for GC-rich dsDNA. Moreover, we demonstrated that the nanoscale perturbations in dsDNA topology are reflected by changes in the microscale properties of the cell, as even short exposition to doxorubicin resulted in an increase in nuclei stiffness, which can be due to aberration of the chromatin organization, upon intercalation of doxorubicin molecules.

Analytical model of the optical vortex microscope.

This paper presents an analytical model of the optical vortex scanning microscope. In this microscope the Gaussian beam with an embedded optical vortex is focused into the sample plane. Additionally, the optical vortex can be moved inside the beam, which allows fine scanning of the sample. We provide an analytical solution of the whole path of the beam in the system (within paraxial approximation)-from the vortex lens to the observation plane situated on the CCD camera. The calculations are performed step by step from one optical element to the next. We show that at each step, the expression for light complex amplitude has the same form with only four coefficients modified. We also derive a simple expression for the vortex trajectory of small vortex displacements.

Moving average process underlying the holographic-optical-tweezers experiments.

We study the statistical properties of recordings that contain time-dependent positions of a bead trapped in optical tweezers. Analysis of such a time series indicates that the commonly accepted model, i.e., the autoregressive process of first-order, is not sufficient to fit the data. We show the presence of a first-order moving average part in the dynamical model of the system. We explain the origin of this part as an influence of the high-frequency CCD camera on the measurements. We show that this influence evidently depends on the applied exposure time. The proposed autoregressive moving average model appears to reflect perfectly all statistical features of the high-frequency recording data.

Cluster formation in ferrofluids induced by holographic optical tweezers.

Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed.

New scanning technique for the optical vortex microscope.

In the optical vortex microscopy the focused Gaussian beam with optical vortex scans a sample. An optical vortex can be introduced into a laser beam with the use of a special optical element--a vortex lens. When moving the vortex lens, the optical vortex changes its position inside the spot formed by a focused laser beam. This effect can be used as a new precise scanning technique. In this paper, we study the optical vortex behavior at the sample plane. We also estimate if the new scanning technique results in observable effects that could be used for a phase object detection.

Micro-step localization using double charge optical vortex interferometer.

We investigate the diffraction effects of focused Gaussian beams yielding a double optical vortex by a nano-step structure fabricated in a transparent media. When approaching such a step the double vortex splits into single ones which move in a characteristic way. By observing this movement we can determine the position of the step with high resolution. Our theoretical predictions were verified experimentally.

Deep microstructure topography characterization with optical vortex interferometer.

We report on a new method of inspecting deep microstructures manufactured in transparent media. Although their lateral dimension (tens of microns) do not exceed the diffraction limit for optical microscopy resolution, their deepness makes the nondestructive measurements practically impossible with presently available methods. We show that the optical vortex interferometer with a vortex generator can be used to differentiate between the samples of good and poor quality. The measurement system is simple and the interpretation of the results is straightforward.

Micro-Dumbbells-A Versatile Tool for Optical Tweezers.

Manipulation of micro- and nano-sized objects with optical tweezers is a well-established, albeit still evolving technique. While many objects can be trapped directly with focused laser beam(s), for some applications indirect manipulation with tweezers-operated tools is preferred. We introduce a simple, versatile micro-tool operated with holographic optical tweezers. The 40 µm long dumbbell-shaped tool, fabricated with two-photon laser 3D photolithography has two beads for efficient optical trapping and a probing spike on one end. We demonstrate fluids viscosity measurements and vibration detection as examples of possible applications.

Alterations of biomechanics in cancer and normal cells induced by doxorubicin.

Mechanical properties of biological structures play an important role in regulating cellular activities and are critical for understanding metabolic processes in cancerous cells and the effects of drugs. For some cancers, such as acute myeloid leukaemia, chemotherapy is one of preferential methods. However, due to the lack of selectivity to cancer cells, cytostatic agents cause toxicity to normal tissues. Here, we study the effect of doxorubicin (DOX) on the mechanical properties of DNA molecules, leukemic blast cells and erythrocytes, using optical tweezers. In addition, we controlled the subcellular distribution of the drug by confocal microscopy. Our results indicated that doxorubicin affects mechanical properties of cellular structures. In all cases the drug reduced mechanical strength of examined objects. For the leukemic cells the drug subcellular distribution was predominantly nuclear with some particulate cytoplasmic fluorescence. In erythrocytes, doxorubicin showed fluorescence mainly in cytoplasm and plasma membrane. The lowering of blast cells stiffness may be due to the interaction of doxorubicin with nuclear structures, especially with nucleic acids, as our studies with DNA confirmed. In addition, it is known that DOX inhibits the polymerization of actin and thus cytoskeletal modification may also be important in reducing of cell mechanical strength. In the case of erythrocytes - the non-nucleated cells, a significant effect on the decrease of cell stiffness, besides the cytoskeleton, may have the interaction of the drug with the cell membrane. Experiments with model phospholipid membranes confirmed that observed increase in cell elasticity originates, among other things, from the drug incorporation in the lipid membrane itself. The lowering of mechanical strength of leukemic cells may have an significant impact on the effectiveness of chemotherapy. However, the fact that doxorubicin interacts not only with proliferating cancer cells, but also with the health ones may explains the high toxicity of the drug at the therapeutic concentrations. Our observations also suggest that chemotherapy with doxorubicin may decrease the risk of vascular complications in acute leukemia, due to increasing the cell elasticity.