Influence of optical "dipoles" on the topological charge of a field with a fractional initial charge.

In this work, using the Rayleigh-Sommerfeld integral and Berry formula, a topological charge (TC) of a Gaussian optical vortex with an initial fractional TC in the far field was calculated. It was found that, for diverse fractional parts of the TC, the beam contained different numbers of screw dislocations, which determined the TC of the entire beam. If a fractional part of the TC was small, the beam consisted of the main optical vortex centered on the optical axis, with the TC equal to the nearest integer (say n>0) and two edge dislocations located on the vertical axis (one above and the other below the center). When the fractional part of the initial TC increased, a "dipole" was formed from the upper edge dislocation, consisting of two vortices with TCs equal to +1 and -1. With a further increase in the fractional part, the additional vortex with TC=+1 moved to the center of the beam, and the vortex with TC=-1 moved to the periphery. When the fractional part of the TC increased further, another "dipole" was formed from the lower edge dislocation, in which, on the contrary, the vortex with TC=-1 was displaced to the optical axis (to the center of the beam) and the vortex with TC=+1 moved to the beam periphery. When the fractional part of the TC became equal to 1/2, the lower vortex with a TC=-1, which was earlier displaced to the center of the beam, began to shift to the periphery, and the upper vortex with a TC=+1 moved closer and closer to the center of the beam, eventually merging with the main vortex when the fractional part approached 1. Such dynamics of additional vortices with TCs above +1 and below -1 determined which whole TC the beam would have (n or n+1) for different values of the fractional part from the segment [n,n+1]. Our analysis has shown that, for any value of the fractional part of the initial topological charge, the TC of the beam in the far field will not be determined. Since, with an increase in the radius of the circle in the beam section on which the TC is calculated, more optical "dipoles" will appear, and the TC will be either n or n+1.

Tight focusing of laser light using a chromium Fresnel zone plate.

Using near-field scanning microscopy, we demonstrate that a 15-µm zone plate fabricated in a 70-nm chromium film sputtered on a glass substrate and having a focal length and outermost zone's width equal to the incident wavelength λ = 532 nm, focuses a circularly polarized Gaussian beam into a circular subwavelength focal spot whose diameter at the full-width of half-maximum intensity is FWHM = 0.47λ. This value is in near-accurate agreement with the FDTD-aided numerical estimate of FWHM = 0.46λ. When focusing a Gaussian beam linearly polarized along the y-axis, an elliptic subwavelength focal spot is experimentally found to measure FWHMx = 0.42λ (estimated value FWHMx = 0.40λ) and FWHMy = 0.64λ. The subwavelength focal spots presented here are the tightest among all attained so far for homogeneously polarized beams by use of non-immersion amplitude zone plates.

Thin high numerical aperture metalens.

We designed, fabricated, and characterized a thin metalens in an amorphous silicon film of diameter 30 µm, focal length equal to the incident wavelength 633 nm. The lens is capable of simultaneously manipulating the state of polarization and phase of incident light. The lens converts a linearly polarized beam into radially polarized light, producing a subwavelength focus. When illuminated with a linearly polarized Gaussian beam, the lens produces a focal spot whose size at full-width half-maximum intensity is 0.49λ and 0.55λ (λ is incident wavelength). The experimental results are in good agreement with the numerical simulation, with the simulated focal spot measuring 0.46λ and 0.52λ. This focal spot is less than all other focal spots obtained using metalenses.

Microlens-aided focusing of linearly and azimuthally polarized laser light.

We have investigated a four-sector transmission polarization converter (4-SPC) for a wavelength of 633 nm, that enables the conversion of a linearly polarized incident beam into a mixture of linearly and azimuthally polarized beams. It was numerically shown that by placing a Fresnel zone plate of focal length 532 nm immediately after the 4-SPC, the incident light can be focused into an oblong subwavelength focal spot whose size is smaller than the diffraction limit (with width and breadth, respectively, measuring FWHM = 0.28λ and FWHM = 0.45λ, where λ is the incident wavelength and FWHM stands for full-width at half maximum of the intensity). After passing through the 4-SPC, light propagates in free space over a distance of 300 µm before being focused by a Fresnel zone plate (ZP), resulting in focal spot measuring 0.42λ and 0.81λ. The focal spot was measured by a near-field microscope SNOM, and the transverse E-field component of the focal spot was calculated to be 0.42λ and 0.59λ. This numerical result was verified experimentally, giving a focal spot of smaller and larger size, respectively, measuring 0.46λ and 0.57λ. To our knowledge, this is the first implementation of polarization conversion and subwavelength focusing of light using a pair of transmission micro-optic elements.

Hyperbolic secant slit lens for subwavelength focusing of light.

Using the finite-difference time-domain simulation, we show that if a gradient-index or binary planar dielectric microlens that focuses light at the output surface has a near-focus subwavelength slit the focal spot width is determined by the slit width. Notably, the slit allows the output light proportion to be increased due to the surface wave scattering, thus forming a focal spot nearly devoid of side lobes. In this work, the focal spot width of λ/23 and the diffraction efficiency of focusing of 44% are achieved.

Analytical expression for radiation forces on a dielectric cylinder illuminated by a cylindrical Gaussian beam.

Radiation forces exerted upon a dielectric, circular-shaped cylinder of infinite length illuminated by a non-paraxial cylindrical Gaussian beam are considered. Vectorial projections of the radiation pressure force on a dielectric, arbitrary- and circular-shaped cylinder are expressed analytically. In particular, the radiation force is expressed through coefficients of the decomposition of the non-paraxial Gaussian beam into the cylindrical functions. Using numerical examples, a possibility to optically trap a circular-shaped cylinder in a non-paraxial cylindrical Gaussian beam is demonstrated.

[Comparison of various approaches to the determination of the products of lipid peroxidation in heptane-isopropanol extracts of blood]. / Sopostavlenie razlichnykh podkhodov k opredeleniiu produktov perekisnogo okisleniia lipidov v heptan-izopropanol'nykh ékstraktakh krovi.

Diagnostic and prognostic validity of lipid peroxidation products estimation was studied in heptane-isopropanol extracts of blood from healthy persons and patients with burns. Different techniques for evaluation of concentration of lipid peroxidation products were comparatively studied. Distinct correlation was found in the weight ratio of individual patterns of lipid peroxidation. Estimation of lipid peroxidation products in the isopropanol extracted phase of blood from patients with burns was of diagnostically important.

[The reaction to heparin in patients with burn toxemia during extracorporeal detoxification]. / Osobennosti reaktsii na geparin u bol'nyh s ozhogovoi toksemiei pri ékstrakorporal'noi detoksikatsii.

The comparison of sensitivity to heparin before hemosorption in burn patients with high level of the blood middle molecular peptides before the operation on the heart in patients with rheumatic cardiac defect without changes in the blood peptide level was carried out. In the model experiments, the influence of a fraction of the middle molecular peptides obtained from the blood of healthy and burned dogs on the effects of heparin and protamine sulfate, and as well on thrombocytic aggregation was studied. The role of the middle molecular peptides in the alteration of response to heparin in burn disease is discussed.

[Effect of thermal injury and middle molecular weight peptides on plasma chemiluminescence]. / Vliianie termicheskoi travmy i srednemolekuliarnykh peptidov na khemiliuminestsentsiiu plazmy krovi.

Thermic trauma altered the most of patterns of blood plasma chemoluminescence, which appear to occur as a result of specific shifts in metabolic dynamics in the patients with burns trauma. The patterns of blood chemoluminescence may reflect not only the rate of free radical reactions and lipid peroxidation but as well as the specific response of the neuro-humoral system to trauma. Alterations in content of middle molecular peptides in blood might be among factors responsible for the chemoluminescence intensity.