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.
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.
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.
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)].
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.
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.
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.
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.
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.
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.
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.