The use of optical vortices in fiber-optic communication lines is a promising direction, particularly for multiplexer creation. To generate an optical vortex and input/output it into/from the fiber, we utilized a biaxial crystal positioned between two parallel polarizers (a "sandwich" configuration). In our experiment, we employed a single-mode fiber and a He-Ne laser with a wavelength of 633 nm. For optical fiber communication, a similar approach involves using a multimode fiber with a core diameter of 20 μm, which allows the propagation of first and second-order vortices at a wavelength of 1550 nm. Based on the research results, the following conclusions can be drawn: a single singularity propagates better in the fiber than two simultaneously. This indicates that for a single singularity, the input beam apertures are better matched, whereas for two singularities, the input aperture is insufficient.
We have studied the formation of energy optical flows with phase singularities using a biaxial crystal during the propagation of light along its optical axes. We have expanded the theoretical foundations for forming a conoscope image in a biaxial crystal, as developed by Berry, to cover the case of arbitrary orientation of polarization elements. It has been shown that increasing the thickness of the crystal enhances the intensity gradient in the phase singularity, thereby enabling more reliable trapping and manipulation of nanoparticles. Reducing the scale of the phase singularity results in a sharper intensity distribution within the singularity, allowing for the capture of smaller nanoparticles.
We proposed an experimental method for determining the localization of phase field singularities. The method consists in measuring the correlation functions of the field and intensity for local fields by several pixels, calculating the ratio of their correlation radii and pixel-by-pixel binding of these parameters to the entire field. Computer simulations and experimental studies have shown that for practically all developed speckle fields, the ratio of the correlation radii saturates in the far detection zone at a value of about 0.64–0.7.
Peculiarities of the spatial behavior of the amplitude zero resulting from scattering of coherent radiation at random rough surfaces are studied. The optical correlation technique is proposed for diagnostics of phase singularities at a complex speckle field. It is shown that the coordinate distribution of the phase singularities at the field with coaxially imposed reference wave provides visualization of strongly scattering objects.
We demonstrate a simple scheme for generation and control of microbubbles using a focused beam of a continuous infrared laser. The main mechanisms of manipulation of microbubbles are based on thermal and optical phenomena. The bubble moves towards the maximum heat and towards the minimum light intensity. We adjusted the ratio between thermal and optical forces, the values of the energy density of the focused beam, at constant laser power. In this case, the bubbles moved from the periphery of the beam to its center and vice versa. Displacements of bubbles also occurred during the change of azimuth of linear polarization of the incident beam.
The article contains the results of the investigation of light scattering on a half cylinder. As a result of numerical modulation, the formation of a zigzag photon jet was shown. was demonstrated. It was demonstrated that he zigzag shape of the photon jet is stable in a wide range (380- 410 ) of the angle of rotation of the half-cylinder. It was found that the minimum value of the half-width of the photon jet is approximately equal tо the diffraction limit, which opens up prospects for the use of the half cylinder as advanced optical tweezers.
The relationship between statistical structure parameters of rough surface and associated correlation parameters of scattered field is based on the model of random phase object. We propose two technique for measuring surface roughness of mirror, which use measurement of a the contrast of the interference pattern in a field, as well as the devices implementing those techniques. One of them is based on measurement of a phase variance of the boundary object field while another of them is based on measurement of a transverse coherence function of a field. The sensitivity limit of the method in measuring the standard deviation of surface profile from base line is about 2 nm.
An interference method for measuring relative phase shift between orthogonally linearly polarized beams at total internal reflection with accuracy of 0.6 rad was proposed at this paper. We experimentally showed that it is impossible to determine the relative longitudinal displacement between beams with orthogonal linear polarizations at total internal reflection by the phase difference in the interferometer. The method developed by us could be useful in measurement of the reflected beam phase, to control the surface homogeneity, and to measure the refraction index of the prism.
Beam colouring effects traversing a different light-scattering medium based on liquid crystals experimental investigations are presented. It was first time shown that the result of the beam colouring at the medium output depends on the singly forward scattered partial signals phase delays magnitudes. Colouring effects spectral investigation has been carried out using both nematic liquid crystals with carbon nanotubes and the solution of liquid crystal in a polymer matrix which was previously investigated. The non-scattered and the singly forward scattered interfering components amplitude ratio significantly affects the colour intensity in both samples. It has further been established that the spectral content of the illuminating beam strongly influences the colour of the resulting radiation. The colouring effect significant increase has been achieved due to the injection of carbon nanotubes, as well as the sensitivity of the liquid crystal to the control electric field has increased.
We investigated the effectiveness of the penetration of CNDs of various sizes into the articular cartilage of various degrees of degeneration affected by osteoarthritis. We performed quantitative evaluations by the intensity of the fluorescent image of the degenerated area of the articular cartilage in vitro. Using colorimetric MTT assay, we found that our CNDs did not have cytotoxic effects on the cellular level in vitro, and this allowed us to emphasize the prospects for using these nanoparticles as dyes for a considerable amount of observation time.
We demonstrate a simple scheme for generation phase singularities are coupled with the vortex-like orbital flows based on a biaxial crystal. Using a shear interferometer, we were able to create a self-converging trap from the phase singularity, which allows converging and diverging two absorbing particles. Moreover, in a certain interferometer shear mode, we were able to multiplex the trap.
The optical properties of single-layer graphene-water complex with the help of powerful laser beam were investigated. According to the investigation an increase of light absorption by the sample was observed. Two possible causes of such anomalous absorption were considered: the doping process of single-layer graphene by the water molecules, and the scattering of optical radiation by microbubbles formed as a result of heating process of the monolayer. The obtained results demonstrated their simultaneous action.
A method is described for the generation of micrometer-sized vapor-gas bubbles in a water suspension containing absorptive pigment nanoparticles. The diluted suspension absorbs the continuous laser radiation (wavelength 808 nm), and each particle in the best illuminated volume serves a bubble-nucleation center. The bubbles can stably exist within or near the illuminated area where their location is governed by the competition between thermal and optical forces and can be controlled via the laser beam parameters. The method enables controllable creation, support, prescribed transportation and destruction of the bubbles.
Manuscript presents the results of study the anomalous light absorption by a system: graphene monolayer on the water surface. Properties of single-layer graphene-water complex were investigated with the help of powerful laser beam. According to the investigation, an increase in light absorption by the sample was observed. Two possible causes of such anomalous absorption were considered: the doping process of single-layer graphene by the water molecules, and the scattering of optical radiation by microbubbles formed as a result of heating process of the monolayer.
The influence of an evanescent field formed by two evanescent waves under the total internal reflection on the dynamics of motion of separate erythrocyte into blood plasma is demonstrated. Computer simulation of red blood cell motion into evanescent field and experimental demonstration of rotational and rectilinear motion expand the possibilities of using optical evanescent waves in applied tasks of nanophysics and biomedicine. The vertical spin produced by the illumination of a cell by the linearly polarized wave with the azimuth of polarization 45º demonstrates unique ability to control transverse motion of the nanoobject that is not characterized to the action of spin momentum inherent to the classical circular polarized optical beam.
We demonstrate a scheme based on a biaxial crystal for generation of the orbital and spin flows in optical fields. Such fields offer a possibility for microparticles’ rotation. By using the spin flow of beams with a gradient trap, refractive dielectric particles can be rotated. We achieved the orbital rotation of such particle due to the combination of an optical vortex trap and a gradient trap in orthogonal linearly polarized incoherent beams. We quantitatively compared the action of the spin and orbital momenta on the same particle of gamboge for its rotational speed.
Experimental investigations of the effects of colouring of a beam traversing a light-scattering medium is presented. It is shown that the result of colouring of the beam at the output of the medium depends on the magnitudes of the phase delays of the singly forward scattered partial signals. Spectral investigation of the effects of colouring has been carried out using a solution of liquid crystal in a polymer matrix. The amplitude ratio of the non-scattered and the singly forward scattered interfering components significantly affects the colour intensity. It has further been established that the spectral content of the illuminating beam strongly influences the colour of the resulting radiation.
Physical existence of the recently discovered vertical spin arising in an evanescent light wave due to the total internal reflection of a linearly polarized probing beam with azimuthal angle 45° is experimentally verified. Mechanical action, caused by optical force, associated with the extraordinary transverse component of the spin in evanescent wave is demonstrated. The motion of a birefringent plate in a direction controlled by simultaneous action of the canonical momentum and the transversal spin momentum is observed. The contribution of the canonical and spin momenta in determination of the trajectory of the resulting motion occur commensurable under exceptionally delicately determined experimental conditions.
Micrometer-sized vapor bubbles are formed due to local heating of the water suspension containing absorptive pigment particles of 100 nm diameter. The heating is performed by the CW near-infrared laser radiation. By changing the laser power, four regimes are realized: (1) bubble generation, (2) stable growth of the existing bubbles; (3) stationary existence of the bubbles and (4) bubbles’ shrinkage and collapse. The generation and evolution of single bubbles and ensembles of bubbles with controllable sizes and numbers is demonstrated. The bubbles are grouped within the laserilluminated region. They can be easily moved and transported together with the focal spot. The results can be useful for applications associated with the precise manipulation and the species delivery in nano- and micro-engineering problems.
We demonstrate a simple scheme for generation the internal energy flows in optical fields based on a biaxial crystal. Such fields offer a variety of possibilities for microparticles’ trapping and control, for example: the intensity minima (maxima) due to the gradient forces; phase singularities are coupled with the vortex-like orbital flows; both the orbital and spin flows; the spin angular momentum density of the field may induce controllable spinning motion of particles; the output field pattern can be easily modified via the controllable input and output polarization, which provides suitable means for fine spatial positioning of the trapped particles.
This report is devoted to simulation of speckle field dynamics during coherent light scattering by the cement surface in the process of setting and hardening. Cement particles are represented by the spheres, which sizes and reflection indexes are changing during the hydration process. The study of intensity fluctuations of scattered coherent radiation – it is a technique, that is quite suitable for the analysis not only fast, but also slow processes of mineral binders hydration and polycrystalline structures creation in the process of hardening. The results of simulation are in good agreement with the experimental results.
Mechanical action caused by the optical forces connected with the canonical momentum density associated with the local wavevector or Belifante’s spin angular momentum, the helicity dependent and the helicity independent forces determined by spin momenta of different nature open attractive prospects to use optical structures for manipulating with minute quantities of matter that is of importance in nanophysics, nanooptics and nanotechnologies, precision chemistry and pharmacology and in numerous other areas. The main finding of our study consists in direct experimental demonstration of physical reality and mechanical action of recently discovered extraordinary transverse component of the spin angular momentum arising (in our case) in an evanescent light wave due to the total internal reflection of linearly polarized probing beam with azimuth 450 at the interface ‘birefringent plate–air’, which is oriented perpendicularly to the wave vector of an evanescent wave.
Within this work we propose a new technique for diagnostics of dispersed media using the shock waves generated with continuous laser radiation of moderate power. Within this technique it is possible to determine geometrical sizes of the dispersed particles as well as the absorption coefficient of the disperse medium. Under long-term influence of the optical field of power less than 100 mW observable disperse medium is not destroyed which can be applied in the micro- and nanotechnologies and in biomedicine.
Water suspension of light-absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities favorable for optical treatment of organic and biological objects. We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the incident light, here being strongly sensitive to the medium position with respect to the focus.
We analyze the effects of coloring of a beam traversing a light-scattering medium. Spectral investigation of the effects of coloring has been carried out using a solution of liquid crystal in a polymer matrix (PDLC). It is shown that the result of coloring of the beam at the output of the medium depends on the magnitudes of the phase delays of the singly forward scattered partial signals. We consider the influence of interference coloring effect on the transmission scattering and spatial-frequency filtering of the radiation which has passed through the PDLC.
Optical correlation technique of cement particle size distribution determining is described. It is based on transverse coherent function measuring using a polarization transverse shearing interferometer. It is shown that set of particles with random form can be substituted with set of spherical particles. This result was obtained by simulation of different particles sets with different forms and orientations. The proposed technique of data processing decreases dependence of the result on interferometer noise, emission source intensity fluctuations and difference of refractive index magnitudes of different cement particles. Described technique allows fast and reliable determining the size distribution function of cement particles.
Focusing the continuous laser radiation on the water with absorbing particles results in the emergence of shock waves and medium blooming periodic in time. The illuminating beam diameter growth at the constant laser power results in the decrease of the signals’ modulation frequency, improving their stability and increasing their amplitudes. The decrease of signal’s modulation frequency is caused by the growth of time, which is needed for heating the medium to the critical temperature. Improving the stability and the increase of optical and acoustic signals’ amplitudes take place due to the growth of the number of particles participating in cavitation.
Water suspension of absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities, which is applicable to optical treatment of biological objects. The experiment was dedicated to the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the falling light, depending strongly on the medium position with respect to the focus.
Experimental investigations of the effects of colouring of a beam traversing a light-scattering medium is presented. It is shown that the result of colouring of the beam at the output of the medium depends on the magnitudes of the phase delays of the singly forward scattered partial signals. Spectral investigation of the effects of colouring has been carried out using a solution of liquid crystal in a polymer matrix. The amplitude ratio of the non-scattered and the singly forward scattered interfering components significantly affects the colour intensity. It has further been established that the spectral content of the illuminating beam strongly influences the colour of the resulting radiation.
In this paper, we propose optical tweezers based on a biaxial crystal. To control the movement of opaque particles, we use the shift polarization interferometer. The results of experimental study of laser tweezers are shown. We demonstrates movement of a microparticle of toner using singular-optical trap, rotate a particle due to orbital momentum, conversion of two traps when changing the plane of polarizer transmission and converging of two traps.
Non-spherical dielectric microparticles were suspended in the water-filled cell and exposed to the coherent Gaussian light beam with switchable state of polarization. When the beam polarization is linear, the particles were trapped at certain off-axial position within the beam cross section. After switching to the right (left) circular polarization, the particles performed spinning motion in agreement with the angular momentum imparted by the field, but also they were involved in the orbital rotation around the beam axis, which in previous works [Y. Zhao et al, Phys. Rev. Lett. 99, 073901 (2007)] was treated as an evidence for the spin-to orbital angular momentum conversion. Since in our situation the moderate focusing of the beam excluded possibility of such a conversion, we treat the observed particle behaviour as a demonstration of the macroscopic “spin energy flow” predicted by the theory of inhomogeneously polarized paraxial beams [A. Bekshaev et al, J. Opt. 13, 053001 (2011)].
It is known that internal energy flow in a light beam can be divided into the orbital flow, associated with the macroscopic
energy redistribution within the beam, and the spin flow originating from instantaneous rotation of the field vectors
inherent in circular or elliptic polarization. In contrast to the orbital one, experimental observation of the spin flow
constituent seemed problematic because (i) it does not manifest itself in the visible transformation of the beam profile
and (ii) it converts into the orbital flow upon tight focusing of the beam, usually employed for the energy flow detection
by the mechanical action on probe particles. We propose a two-beam interference technique that permits to obtain
appreciable level of the spin flow in moderately focused beams and to detect the orbital motion of probe particles within
a field where the transverse energy circulation is associated exclusively with the spin flow. This result can be treated as
the first demonstration of mechanical action of the spin flow of a light field.
We investigate scattering indicatrix and Mueller matrix elements of scattered radiation for different voltages applying to
the polymer dispersed liquid crystals cell. We observe modulation of scattering indicatrix and Mueller matrix elements
with period equals to 2.5°. We calculate the size of LC drops in polymer matrix that equals to 7.25 μm which is confirmed
by microscopic research. We construct spatial frequency filter for separation of large and small details of images.
This paper is devoted to simulation of speckle field dynamics during coherent light scattering by the cement surface in
the process of hydration. Cement particles are represented by the spheres which sizes and reflection indexes are changing
during the hydration process. The results of this simulation are in good agreement with the experimental results.
The method of concrete hydration stages diagnostics was designed. Diagnostics was based on piezoelectric photoacoustic
detection. Experimental data, which demonstrate amplitude changing dynamics of photoacoustic signal in concrete
during the hydration process, were showed.
The feasibilities for optical correlation diagnostics of a rough surface with large surface inhomogeneities by determining the
transformations of the longitudinal coherence function of the field scattered by such surface are substantiated and
implemented. The algorithm of computer processing of the interferograms for reconstruction of the relief of regular surfaces
with resolution 0.5 nm is represented.
Thorough description of diaphragm size selection for detecting the intensity of laser beam scattered on surface of
congelating cement was given. Also fluctuations of speckle-field and its connection with square derivative of intensity
were investigated. Analysis was based on CCD images of speckle-field dynamics in process of cement hydratation.
The results of experimental study of fluctuations of a coherent field intensity during hardening of concrete are presented. It has been shown that square time derivative of fluctuations of a scattered field intensity are connected with base stages of cement hydratation.
The results of experimental study of fluctuations of a coherent field intensity during hardening of concrete are presented.
It has been shown that square time derivative of fluctuations of a scattered field intensity are connected with base stages
of cement hydratation.
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