Metalenses for the generation of vector Lissajous beams with a complex Poynting vector density.

We propose a method for the design of metalenses generating and focusing so-called vector Lissajous beams (VLBs), a generalization of cylindrical vector beams (CVBs) in the form of vector beams whose polarization vector is defined by two orders (p, q). The designed metalenses consist of subwavelength gratings performing the polarization transformation of the incident linearly polarized laser beams and a sublinearly chirped lens term for the realization of the beam focusing. The possibility of using VLBs for the realization of laser beams with a complex Poynting vector is theoretically shown. The certain choice of orders (p, q) of the generated VLBs makes it possible to control the type of various electromagnetic field components as well as the components of the complex Poynting vector. For example, in contrast to VLBs, the classical types of CVBs cannot provide an imaginary part in the longitudinal component of the Poynting vector. Such light fields are promising for exciting non-standard forces acting on the trapped nano- and microparticles.

Spectral control of the orbital angular momentum of a laser beam based on 3D properties of spiral phase plates fabricated for an infrared wavelength.

This paper examines the spectral properties of a spiral phase plate (SPP) generating orbital angular momentum (OAM) beams. A simple method is proposed for calculating the resulting OAM by measuring only two maximum expansion coefficients. A comparative numerical simulation of the proposed and traditional methods is performed. An SPP is fabricated for generation of an OAM with integer values at infrared and visible wavelengths. Qualitative experimental studies of the changes in a generated OAM with a change in the operating wavelength are performed using the spatial filtering method. The experimental results are found to agree with the results of numerical simulation. Beams with integer and fractional OAM values are obtained experimentally by changing the wavelength.

Vector Lissajous laser beams.

We consider a new type of vector beam, the vector Lissajous beams (VLB), which is of double order (p,q) and a generalization of cylindrical vector beams characterized by single-order p. The transverse components of VLBs have an angular relationship corresponding to Lissajous curves. A theoretical and numerical analysis of VLBs was performed, showing that the ratio and parity of orders (p,q) affect the properties of different components of the electromagnetic field (EF) (whether they be real, imaginary, or complex). In addition, this allows one to engineer the imaginary part of the longitudinal component of the electromagnetic field and control the local spin angular momentum density, which is useful for optical tweezers and future spintronics applications.

Influence of optical forces induced by paraxial vortex Gaussian beams on the formation of a microrelief on carbazole-containing azopolymer films.

The paper discusses photoinduced microrelief formation in a film of an azopolymer. A theoretical study of the effect of laser beam polarization on the balance of optical forces acting under the direct action of paraxial Gaussian beams on the irradiated substance was made. We show that taking into account the gradient and scattering components of the force does not allow us to correctly describe the shape of the microasperities obtained on a carbazole-containing azopolymer. An approximation function is presented that describes the dependence of the microasperities' shapes on the non-gradient component of the optical force of laser radiation in the absence and presence of a vortex phase. A comparative analysis of the approximation results and experimentally obtained microreliefs was carried out.

Increased reverse energy flux area when focusing a linearly polarized annular beam with binary plates.

We suggest an annular field with linear polarization and a binary sectored phase for the formation of the inverse energy flux with an increased area of action. The possibility of the formation of a reverse energy flux over large areas in the focal domain at tight focusing of a linearly polarized field with the binary phase is shown theoretically and numerically. Moreover, the area increases with the number m. The proposed approach is simple, because linearly polarized radiation is the most common among laser sources and does not require additional devices for polarization transformations. The binary phase also provides ease of manufacture of phase plates with a high diffraction efficiency and high damage threshold. The results will be useful in optical manipulations and processing.

Dynamic focal shift and extending depth of focus based on the masking of the illuminating beam and using an adjustable axicon.

We investigate several methods of focus shift and focus extension in detail. These methods are divided into two groups: (1) changing the radius of the illuminating beam and/or limiting diaphragm; and (2) adding an optical system with an adjustable element (lens or axicon). In the cases of a planar and Gaussian illuminating beam, values of the focus position and depth of focus (DOF) are calculated theoretically and numerically, depending on the beam radius. In addition, theoretical and numerical evaluations of displacement and DOF increase for the focusing system with the adjustable lens or axicon obtained. We show that these methods for changing the parameters of the focal area provide flexibility and efficiency in the control of its characteristics. Recommendations about possible applications in which such control is important are formulated on the basis of the results obtained.

Binary multi-order diffraction optical elements with variable fill factor for the formation and detection of optical vortices of arbitrary order.

In this paper we consider the calculation of binary diffraction optical elements (DOEs) for the formation and detection of optical vortices of arbitrary order. The synthesis of binary DOEs is based on a combination of the method of carrier spatial frequencies and binary coding with a variable fill factor. Unlike various methods of multiplication, the method of carrier spatial frequencies is characterized by great flexibility and versatility. It allows us to not only form the given field distributions in arbitrary diffraction orders, but also to give them arbitrary weight ratio (energy distribution in orders). As a rule, such universality leads to the need to form a complex amplitude-phase distribution in the input plane. To avoid this, in this paper it is proposed to use binary coding with a variable level. The effect of such coding is studied in detail both theoretically and numerically. It is shown that the level variation makes it possible to change the set of the observed diffraction orders. The positions and orders of the optical vortices formed are uniquely determined by the values of the carrying spatial frequencies and the topological charges of the vortices in the basic order. The results can be useful in optical communications.

Generalized parabolic nondiffracting beams of two orders.

In this paper we consider a generalization of standard nondiffracting parabolic beams. The proposed generalized beams have two orders: a continuous parameter a, as in standard beams, and the new parameter is an integer index m. Physically, the last parameter is equal to the number of rotated repetitions of the structure of the original angular spectrum on the total circle in the frequency space. Theoretical investigation shows that for a=0 the beams are real functions and have a symmetry of order 2m. If a≠0 the beams will be real functions only for odd values of m. Moreover, in this case the beams have a symmetry of order m, while for even values of m the order of symmetry is 2m. The results of numerical simulation confirm these conclusions. Examples of generalized traveling parabolic waves, which are formed on the basis of generalized static parabolic beams, are also given.

Aberration laser beams with autofocusing properties.

We investigate theoretically, numerically, and experimentally a novel type of laser beam-an aberration laser beam (ALB). To generate the ALB, a diffractive optical element with a phase transmission function having an arbitrary radial dependence of power q and a periodic angular dependence of sin(mϕ) or cos(mϕ) form can be used. Such a light distribution is more general than classic aberrations including Zernike polynomials. We demonstrate that such radial nonuniformity results in autofocusing properties of ALBs. The autofocusing feature of ALBs is analogous to that of circular Airy beams, but the ALBs' autofocusing feature has more flexibility. The presence of the periodic angular dependence in the phase results in a diffraction pattern with mth-order symmetry. Transformation of ALBs during propagation in free space is analogous to transformation of the three-Airy beams; however, the generated light distributions have an arbitrary integer order of symmetry. The presence of an additional focusing lens leads to formation of an optical field in its focal plane with symmetry that depends on the parity of m: for even m, the generated light distribution has 2mth-order symmetry, and, for odd m, it has mth-order symmetry.

Focused, evanescent, hollow, and collimated beams formed by microaxicons with different conical angles.

Diffraction patterns formed by axicons with different tip (vertex) angles are analytically and numerically investigated. Results show that the axicon (or tapered dielectric probe) can form an extended axial light beam, a compact evanescent field, a hollow beam, and a collimated beam, depending on the vertex angle. Two-dimensional and three-dimensional models of a tapered dielectric probe show that, with small changes to the vertex angle, light transmitted by the probe is scattered rather than focused, and vice versa. Angle meanings corresponded to boundary transitions have a quantum character and densify as the angle approaches zero. These features should be taken into consideration when manufacturing microaxicons intended for various applications.

Comparison of satisfaction with care between two different models of HIV care delivery in St. Petersburg, Russia.

Prior to 2010, medical care for people living with HIV/AIDS was provided at an outpatient facility near the center of St. Petersburg. Since then, HIV specialty clinics have been established in more outlying regions of the city. The study examined the effect of this decentralization of HIV care on patients' satisfaction with care in clinics of St. Petersburg, Russia. We conducted a cross-sectional study with 418 HIV-positive patients receiving care at the St. Petersburg AIDS Center or at District Infectious Disease Departments (centralized and decentralized models, respectively). Face-to-face interviews included questions about psychosocial characteristics, patient's satisfaction with care, and clinic-related patient experience. Abstraction of medical records provided information on patients' viral load. To compare centralized and decentralized models of care delivery, we performed bivariate and multivariate analysis. Clients of District Infectious Disease Departments spent less time in lines and traveling to reach the clinic, and they had stronger relationships with their doctor. The overall satisfaction with care was high, with 86% of the sample reporting high level of satisfaction. Nevertheless, satisfaction with care was strongly and positively associated with the decentralized model of care and Patient-Doctor Relationship Score. Patient experience elements such as waiting time, travel time, and number of services used were not significant factors related to satisfaction. Given the positive association of satisfaction with decentralized service delivery, it is worth exploring decentralization as one way of improving healthcare services for people living with HIV/AIDS.

Depression, substance use, viral load, and CD4+ count among patients who continued or left antiretroviral therapy for HIV in St. Petersburg, Russian Federation.

Antiretroviral therapy (ART) became more widely available in the Russian Federation in 2006 when the Global Fund made a contribution to purchase ART with a mandate to increase numbers of patients receiving it. Funds were distributed to AIDS Centers and selected hospitals, and numbers quickly increased. Though ART is highly effective for adherent patients, dropout has been a problem; thus understanding characteristics of patients who remain on ART vs. those who leave treatment may provide information to facilitate engagement. We retrospectively assessed depression, hopelessness, substance use, viral load, and CD4+ counts of 120 patients who dropped out of ART for ≥12 months (Lost-to-Care, LTCs) and 120 who continued for ≥12 months (Engaged-in-Care, EICs). As expected, LTCs had higher viral loads and depression, lower CD4+ counts, more alcohol, heroin, and injection drug use in the past 30 days. A binary logistic regression with Center for Epidemiologic Studies Depression score, Beck Hopelessness score, whether drugs/alcohol had ever prevented them from taking ART, and past 30 days' alcohol use [χ(2)(4) = 64.27, p = .0.000] correctly classified 74.5% of participants as LTC or EIC, suggesting that integrated treatment for substance use, psychiatric, and HIV could reduce dropout and improve outcomes.

Local foci of a parabolic binary diffraction lens.

The intensity distribution on the optical axis of a parabolic binary diffraction lens is theoretically and experimentally studied. The binary diffraction lens is shown to form an array of focal spots of near-equal intensity on the optical axis. In each local focus, the focal-spot size decreases as the square of the focus number until the paraxiality condition is broken. Theory and experiment are shown to be in good agreement.

Generation of Complex Transverse Energy Flow Distributions with Autofocusing Optical Vortex Beams.

Optical vortex (OV) beams are widely used for the generation of light fields with transverse energy flow inducing orbital motion of the nano- and microparticles in the transverse plane. Here, we present some new modifications of OV beams with autofocusing properties for shaping complex transverse energy flow distributions varying in space. The angular component of the complex amplitude of these beams is defined by the superpositions of OV beams with different topological charges. The proposed approach provides a convenient method to control the three-dimensional structure of the generated autofocusing OV beams. The control of the transverse distribution of an autofocusing beam provides a wide variety of generated fields with both rotating and periodic properties, which can be used in the field of laser manipulation and laser material processing. Thus, the obtained numerical results predict different types of motion of the trapped particles for the designed OV autofocusing beams. The experimental results agree with modeling results and demonstrate the principal possibility to shape such laser beams using spatial light modulators.

Formation of hybrid higher-order cylindrical vector beams using binary multi-sector phase plates.

Nowadays, the well-known cylindrical vector beams (CVBs) - the axially symmetric beam solution to the full-vector electromagnetic wave equation - are widely used for advanced laser material processing, optical manipulation and communication and have a great interest for data storage. Higher-order CVBs with polarisation order greater than one and superpositions of CVBs of various orders (hybrid CVBs) are especially of interest because of their great potential in contemporary optics. We performed a theoretical analysis of the transformation of first-order CVBs (radially and azimuthally polarised beams) into hybrid higher-order ones using phase elements with complex transmission functions in the form of the cosine or sine functions of the azimuthal angle. Binary multi-sector phase plates approximating such transmission functions were fabricated and experimentally investigated. The influence of the number of sectors and a height difference between neighbouring sectors, as well as the energy contribution of the different components in the generated hybrid higher-order CVBs were discussed in the context of polarisation transformation and vector optical field transformation in the focal region. The possibility of polarisation transformation, even in the case of weak focusing, is also demonstrated. The simple structure of the profile of such plates, their high diffraction efficiency and high damage threshold, as well as the easy-to-implement polarisation transformation principle provide advanced opportunities for high-efficient, quickly-switchable dynamic control of the generation of structured laser beams.

Polarization conversion when focusing cylindrically polarized vortex beams.

Currently, cylindrical beams with radial or azimuthal polarization are being used successfully for the optical manipulation of micro- and nano-particles as well as in microscopy, lithography, nonlinear optics, materials processing, and telecommunication applications. The creation of these laser beams is carried out using segmented polarizing plates, subwavelength gratings, interference, or light modulators. Here, we demonstrate the conversion of cylindrically polarized laser beams from a radial to an azimuthal polarization, or vice versa, by introducing a higher-order vortex phase singularity. To simultaneously generate several vortex phase singularities of different orders, we utilized a multi-order diffractive optical element. Both the theoretical and the experimental results regarding the radiation transmitted through the diffractive optical element show that increasing the order of the phase singularity leads to more efficient conversation of the polarization from radial to azimuthal. This demonstrates a close connection between the polarization and phase states of electromagnetic beams, which has important implications in many optical experiments.