Production of radially and azimuthally polarized polychromatic beams

We describe a system that efficiently provides radially or azimuthally polarized radiation from a randomly polarized source. It is constructed from two conical reflectors and a cylindrical sheet of polarizing film. Envisaged applications include a microscope illuminator for high-resolution surface plasmon resonance microscopy, illumination for high-resolution microlithography, and efficient coupling of a laser source to hollow optical fibers. The angular coherence function of light polarized by the device was measured to evaluate its usefulness for these applications.     

Circular grating coupler for creating focused azimuthally and radially polarized beams

We show a planar optical circuit design that takes light from an input waveguide and creates a focused azimuthally or radially polarized beam emanating from the surface of the substrate. It is implemented in silicon-on-insulator waveguides and does not require any external components to focus the beam. The focal spot size can be subwavelength and is potentially useful for lithography, imaging, optical data storage, optical trapping, optical excitation of molecules, or coupling to optical fibers.     

Forces in optical tweezers with radially and azimuthally polarized trapping beams

It has been suggested that radially polarized beams can be used to improve the performance of optical tweezers, with reduced scattering force resulting from both the polarization and the dark center of the beam [Opt. Lett. 32, 1839 (2007)]. We calculate the forces on particles in such traps, using rigorous electromagnetic theory, comparing the results with azimuthally polarized beam, circularly polarized LG 01 beams, and Gaussian beams. Our results agree qualitatively with Opt. Lett. 32, 1839 (2007), but differ quantitatively.     

Generation of azimuthally and radially polarized beams by coherent polarization beam combination

A new architecture for generating pure azimuthally and radially polarized beams is presented. It involves coherent polarization beam combination of two orthogonally polarized LP(11) fiber modes. Experimental results reveal that high purely polarized (polarization purity of 95% or better) azimuthal and radial beams can be generated.     

A high-efficient method for generating radially and azimuthally polarized Bessel beams using biaxial crystals

As was shown previously, in propagation of a circularly polarized Bessel light beam along the optical axes of a biaxial crystal, there takes place the conversion of the order of Bessel function. In this paper, a new result is presented which is obtained by varying the polarization state of an input beam. Namely, a linearly polarized beam can be transformed into a beam with the radial or azimuthal polarization state. At that the order-transformation also occurs. The switching between radial and azimuthal polarization states of the output beam is performed by the proper switching between two orthogonal linear polarization states of the input beam. The efficiency of polarization conversion is high and can be practically full at an appropriate choice of the cone angle of the input beam or crystal length.     

Propagation and parametric characterization of the polarization structure of paraxial radially and azimuthally polarized beams

Analytical expressions are provided for describing the free-space evolution of the polarization structure of paraxial beams whose electric-field vector at some transverse plane exhibits either a radially or an azimuthally polarized behavior. At each transverse plane, the polarization distribution across the beam profile is characterized by means of two sets of parameters, namely, the so-called (local) radial Stokes representation, and the (overall) percentage of the irradiance associated with the radial and azimuthal field components. The propagation laws for these sets of parameters are also shown. As an illustrative example, a radially polarized beam is analized whose wavefront contains a spiral phase factor.     

Three-dimensional multiple optical cages formed by focusing double-ring shaped radially and azimuthally polarized beams

We propose and simulate a method for generating a three-dimensional(3D) optical cage in the vicinity of focus by focusing a double-ring shaped radially and azimuthally polarized beam. Our study shows that the combination of an inner ring with an azimuthally polarized field and an outer ring with a radially polarized field and a phase factor can produce an optical cage with a dark region enclosed by higher intensity. The shape of the cage can be tailored by appropriately adjusting the parameters of double-mode beams. Furthermore, multiple 3D optical cages can be realized by applying the shift theorem of the Fourier transform and macro-pixel sampling algorithm to a double-ring shaped radially and azimuthally polarized beam.     

Material processing with pulsed radially and azimuthally polarized laser radiation

We report on the generation of radially and azimuthally polarized Q-switched laser radiation and its application in material processing. The power levels were sufficiently high to study micro-hole drilling in different metals. Depending on the optical properties of the metal, either radial or azimuthal polarization shows the best efficiency and the effect is attributed to waveguiding. For steel, a comparison to linearly or circularly polarized laser radiation indicates that the doughnut-shaped beam with azimuthal polarization is the most energy-efficient in producing holes of the same diameter and depth. PACS 79.20.Ds; 29.27.Hj; 81.05.Bx     

Production of radially or azimuthally polarized beams in solid-state lasers and the elimination of thermally induced birefringence effects

Production and amplification of radially and azimuthally (tangentially) polarized laser beams are demonstrated. Based on the different focusing between radially and tangentially polarized light in thermally stressed isotropic laser rods, Nd:YAG laser oscillators were developed to produce low-loss stable oscillation in a single polarization. Pure radially polarized light at 70 W with M2 = 2 and on-axis impure radially polarized light at 150 W with M2 = 2.5 were achieved. The radially polarized beams were then amplified while good beam quality and polarization purity were retained. Complete elimination of thermal-birefringence-induced aberrations was demonstrated. This should allow much better beam quality from rod-based high-power lasers.     

Second harmonic generation polarization microscopy with tightly focused linearly and radially polarized beams

Second harmonic generation microscopy was conducted on rat-tail tendons with linearly and radially polarized beams. Transverse and axial field components were generated in the focal region through tight focusing of linearly and radially polarized. It was found that the generated SHG signals could not be qualitatively explained with a scalar approximation to the electric field at the focus. Only by accounting for the interactions of the axial and transverse components of the electric field interacting through the nonlinear susceptibility χ⁽²⁾ tensor could the SHG images be explained. For the case of collagen we find that the SHG signal varies as a function of the analyzer angle with a cos² or sin² dependency for linearly polarized beams. For tightly focused radially polarized beams we find that the output SHG is radially polarized after collimation and is independent of the analyzer angle.     

Characterizing polarization properties of radially polarized beams

In the present work two methods of characterizing polarization properties of well-known radially polarized beams are discussed in both theoretical aspect and experimental aspect. A rotating linear polarizer used behind the beam is known to be used to qualitatively characterize the polarization properties of a radially polarized beam. In this paper for the first time we give the mathematic model of this characterization process. The proposed model helps to analyze the known experimental results. On the other hand two global parameters have been previously proved to be used to characterize the linear or circular polarization content of the radially polarized beams. In this paper for the first time we propose the theoretical model of determining the two parameters in experiments. Some experimental results on characterizing the polarization properties of the real radially polarized beam produced by using different approaches are shown.     

Waveguide properties of single subwavelength holes demonstrated with radially and azimuthally polarized light

We investigate the transmission of focused beams through single subwavelength holes in a silver film. We use radially and azimuthally polarized light to excite higher-order waveguide modes as well as to match the radial symmetry of the aperture geometry. Remarkably, the transmission properties can be described by a classical waveguide model even for thicknesses of the silver film as thin as a quarter of a wavelength. PACS  42.25.Bs; 42.25.Ja; 42.79.Gn     

Analytical vectorial structure of radially polarized light beams

Starting from the vector angular spectrum of the electromagnetic beam, the analytical vectorial structure of the radially polarized beams (RPBs) is presented. The energy flux distributions of the RPBs are demonstrated. The physical pictures of the RPBs are well illustrated from the vectorial structure. This particular electromagnetic field is entirely transverse magnetic, and on axis it only has a longitudinal (z) electric-field component (i.e., no transverse electric field and no magnetic field at all on axis).     

Tight focusing of radially polarized Gaussian and Bessel-Gauss beams

We examine the effects of tightly focusing a radially polarized beam with uniform, Gaussian, or Bessel-Gauss pupil functions. The resulting FWHM is smallest for the case of a uniform amplitude profile, while the Bessel-Gauss beam results in the largest FWHM. The uniform amplitude profile also results in an axial field component that increases fastest with increasing NA. The ratio of the axial component to the transverse component is also the greatest for the uniform pupil function. On the other hand, the Bessel-Gauss beam benefits the most from the use of an annulus.     

Beam quality changes of radially and azimuthally polarized fields propagating through quartic phase plates

In terms of the so-called irradiance moments of a light field, the beam quality change, ΔQ, of radially and azimuthally polarized beams caused by propagation through a quartic phase plate (as occurs, for example, in strongly pumped laser rods used in high-power solid-state lasers) is studied. Analytical expressions for ΔQ are given, and a comparison between the scalar and vectorial regimes is also shown. The results are applied to several cases of interest.     

Generation of radially polarized beams using spatial light modulator

Radially polarized beams have attracted much attention and found many applications in many optical systems, recently. And generation of radially polarized beams is necessary for experimental research and applications. In this paper, a kind of generation method was proposed. Two beams are obtained by spatial light modulator and pi phase plate, and then interfere to form desirable radially polarized beams. Experimental results show that radially polarized beams are higher property, which shows this kind of interferential generation of radially polarized laser beams work effectively.     

Propagation of radially polarized beams in the oceanic turbulence

Based on the extended Huygens–Fresnel principle and the unified theory of coherence and polarization of light, we investigate the propagation properties of a radially polarized beam through turbulent ocean. Analytic formulae for the spectral density, the spectral degree of polarization, and the beam characteristics of such a beam on propagation are discussed. It is shown that under the influence of oceanic turbulence, the radially polarized beam will change to a partially polarized one and the beam profile will approach to a Gaussian distribution.     

Radially and azimuthally polarized beams generated by space-variant dielectric subwavelength gratings

We present a novel method for forming radially and azimuthally polarized beams by using computer-generated subwavelength dielectric gratings. The elements were deposited upon GaAs substrates and produced beams with a polarization purity of 99.2% at a wavelength of 10.6 microm . We have verified the polarization properties with full space-variant polarization analysis and measurement, and we show that such beams have certain vortexlike properties and that they carry angular momentum.     

Experimental verification on tightly focused radially polarized vortex beams

The theoretical and experimental results of tightly focused radially polarized vortex beams are demonstrated. An auto-focus technology is introduced into the measurement system in order to enhance the measurement precision, and the radially polarized vortex beams are generated by a liquid-crystal polarization converter and a vortex phase plate. The focused fields of radially polarized vortex beams with different topological charges at numerical apertures （NAs） of 0.65 and 0.85 are measured respectively, and the results indicate that the total intensity distribution at focus is dependent not only on the NA of the focusing objective lens and polarization pattern of the beam but also on the topological charge l of the beam. Some unique focusing properties of radially polarized vortex beams with fractional topological charges are presented based on numerical calculations. The experimental verification paves the way for some practical applications of radially polarized vortex beams, such as in optical trapping, near-field microscopy, and material processing.     

Characterization of tightly focused partially coherent radially polarized vortex beams

<正>Tight focusing properties of partially coherent radially polarized vortex beams are studied based on vectorial Debye theory.We focus on the focal properties including the intensity and the partially coherent and polarized properties of such partially coherent vortex beams through a high numerical aperture objective. It is found that the source coherence length and the maximal numerical aperture angle have direct influence on the focal intensity,as well as coherence and polarization properties.This research is important in optical micromanipulation and beam shaping.