Gilad M. Lerman

Demonstration of Nanofocusing by the use of Plasmonic Lens Illuminated with Radially Polarized Light

We experimentally demonstrate the focusing of surface plasmon polaritons by a plasmonic lens illuminated with radially polarized light. The field distribution is characterized by near-field scanning optical microscope. A sharp focal spot corresponding to a zero-order Bessel function is observed. For comparison, the plasmonic lens is also measured with linearly polarized light illumination, resulting in two separated lobes. Finally, we verify that the focal spot maintains its width along the optical axis of the plasmonic lens. The results demonstrate the advantage of using radially polarized light for nanofocusing applications involving surface plasmon polaritons.

Effect of radial polarization and apodization on spot size under tight focusing conditions

We study the effect of polarization and aperture geometry on the focal spot size of a high numerical aperture (NA) aplanatic lens. We show that for a clear aperture geometry, illuminating the lens by linear or circular polarization is preferable over radial polarization for spot size reduction applications. For annular aperture and objective lenses of 0.85 NA and above we give the sizes of the inner annulus which constitute the transition points to a state where the radial polarization illumination gives smaller spot size. We analyze the evolution, the profile and the effect of transverse and longitudinal field components in the focal plane, and show that they play an opposite role on the spot size in the cases of circular and radial polarization illumination. We show that in the limit of a very thin annulus the radial polarization approaches the prediction of the scalar theory at high NA, whereas the linear and circular polarizations deviate from it. We verify that the longitudinal component generated by radially polarized illumination produces the narrowest spot size for wide range of geometries. Finally, we discuss the effects of tight focusing on a dielectric interface and provide some ideas for circumventing the effects of the interface and even utilize them for spot size reduction.

Generation of a radially polarized light beam using space-variant subwavelength gratings at 1064 nm

The generation of radially polarized beams at a wavelength of 1064 nm by the use of a polarization transformer device consisting of space-variant subwavelength gratings (SGs) is demonstrated experimentally. The SG generates a pi phase retardation between the TE and TM polarizations, acting as a half-wave plate, reflecting the polarization vector with respect to the axes of the plate. The polarization transformer is characterized by polarization analysis and by far-field measurements. The characterization results show good agreement with theory. The device is suitable for operation with Nd:YAG lasers; thus it is attractive for biological, optical tweezers, and material processing applications.

Generation and tight focusing of hybridly polarized vector beams

We demonstrate the generation of hybridly polarized beams. Tight focusing analysis show polarization distribution with 3D orientation and space variant ellipticity, which may be useful for particle orientation analysis, microscopy and atomic systems.

Tight focusing of spatially variant vector optical fields with elliptical symmetry of linear polarization

We study the tight-focusing properties of spatially variant vector optical fields with elliptical symmetry of linear polarization. We found the eccentricity of the incident polarized light to be an important parameter providing an additional degree of freedom assisting in controlling the field properties at the focus and allowing matching of the field distribution at the focus to the specific application. Applications of these space-variant polarized beams vary from lithography and optical storage to particle beam trapping and material processing.

Efficient coupling and field enhancement for the nano-scale: plasmonic needle.

Theoretical demonstration of efficient coupling and power concentration of radially-polarized light on a conical tip of plasmonic needle is presented. The metallic needle is grown at the center of radial plasmonic grating, engraved in a metal surface. The electromagnetic field distribution was evaluated by Finite Elements and Finite-Difference-Time-Domain methods. The results show that the field on the tip of the needle is significantly enhanced compared to the field impinging on the grating. The power enhancement exhibited a resonant behavior as a function of needle length and reached values of approximately 10(4). Test samples for few types of characterization schemes were fabricated.

Light transmission through a circular metallic grating under broadband radial and azimuthal polarization illumination

We study light transmission through circular metallic grating under radial/azimuthal polarization illumination and observe strong polarization selectivity and a resonance behavior making it attractive for applications relying on radial polarization.

Near- and far-field properties of plasmonic oligomers under radially and azimuthally polarized light excitation.

We present a comprehensive experimental and theoretical study on the near- and far-field properties of plasmonic oligomers using radially and azimuthally polarized excitation. These unconventional polarization states are perfectly matched to the high spatial symmetry of the oligomers and thus allow for the excitation of some of the highly symmetric eigenmodes of the structures, which cannot be excited by linearly polarized light. In particular, we study hexamer and heptamer structures and strikingly find very similar optical responses, as well as the absence of a Fano resonance. Furthermore, we investigate the near-field distributions of the oligomers using near-field scanning optical microscopy (NSOM). We observe significantly enhanced near-fields, which arise from efficient excitation of the highly symmetric eigenmodes by the radially and azimuthally polarized light fields. Our study opens up possibilities for tailored light-matter interaction, combining the design freedom of complex plasmonic structures with the remarkable properties of radially and azimuthally polarized light fields.

Demonstration of spatially inhomogeneous vector beams with elliptical symmetry

We experimentally demonstrate vector beams having an elliptical symmetry of polarization, breaking the cylindrical symmetry of vector beams (e.g., radially polarized beams). Applications of such beams vary from material processing, lithography, and optical memories to excitation of elliptically shaped nanoparticles and plasmonic structures.

Radial polarization interferometer

We demonstrate an interferometer based on interference of radially and azimuthally polarized beams. The spatially varying intensity provides additional information improving phase change measurements compared with a conventional interferometer.