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Complex Polarization Tailored Light Fields at the Nanoscale - Generation, Description and Reconstruction
Optical Investigation of Single Sub-wavelength Nanostructures - Polarization Tailored Light Fields as a Versatile Tool for Nanooptics
Nanostructure Ensembles and Metamaterials - Optical Investigation and Advanced Nanofabrication

Complex Polarization Tailored Light Fields at the Nanoscale -
Generation, Description and Reconstruction

Keywords: Polarization optics, nanooptics, tight focusing, polarization tailoring, highly confined fields, full-field reconstruction, nanoprobing, knife-edge method, analytical and numerical description

In the InMik group, we study both complex paraxial as well as highly non-paraxial (tightly focused) light fields. For the generation of paraxial light beams with non-homogeneous polarization distribution of high quality, we develop and utilize different types of polarization converters, such as segmented waveplates [1], fiber-based methods [2,3], liquid crystal-based polarization rotators, spatial phase modulators and other techniques (see also full publications list). To create even more complex field distributions with intriguing properties, we focus polarized light beams to a tight diffraction-limited spot. This offers unique possibilities for applications in microscopy and nanophotonics as well as for the study of fundamental light-matter interactions.
To describe the resulting tightly focused light field theoretically, vectorial diffraction theory can be used. In this technique, diffraction integrals have to be solved numerically. In the InMik group, we also study and develop analytical tools for the description of complex focal field distributions. For this purpose, we use the so-called complex source-beam (CSB) model [4,5]. This model allows for a full analytical and vectorial description of tightly focused light beams. By expanding the focal fields into electromagnetic multipoles, the interaction of the light field with sub-wavelength structures can also be studied theoretically [6].
Beside the theoretical description of tightly focused and highly confined field distributions, it is essential to study such complex fields experimentally as well. To profile, for instance, the electric energy density of a focused light beam, the so-called knife-edge method can be adopted. We have shown that this technique, known from beam profilers for paraxial light beams, can also be used in the non-paraxial case by carefully choosing appropriate knife-edge parameters, such as edge material, geometry or thickness [7]. In more recent studies, we have been exploring the light-matter interaction between different types of knife-edges and tightly focused light beams revealing the physical mechanisms which render the knife-edge method extremely sensitive to the choice of the above-mentioned edge parameters [8]. Furthermore, we investigated possible corrections to the analysis method of recorded knife-edge profiling data, to account for the aforementioned effects originating from the interaction of the focused light beam and the knife-edge [9]. This allows for an accurate experimental determination of beam parameters for almost arbitrary edge parameters (material, thickness etc.).
An alternative approach aiming for the measurement of the full vectorial information of the highly confined light fields under study is based on what we call Mie scattering nanointerferometry [10]. This technique relies on the angularly resolved measurement of the light scattered off a single sub-wavelength nanoparticle utilized as a nanoscopic scanning probe. The interference between scattered and incoming light allows for the precise determination of both the amplitude and relative phase distributions of all individual electric field components with deep sub-wavelength resolution, hence providing detailed insight into the fully vectorial nature of the field distribution under study.
Utilizing the above-mentioned techniques does not only allow for a detailed characterization of our experimental setups in terms of aberrations, alignment and beam quality, but also paves the way for the experimental study of novel states of the light field with exotic properties. In the past, our research was concentrated on the focusing properties of linearly polarized light beams [7,11] and cylindrical vector beams, such as radially polarized light beams. Especially radially polarized light beams were proven to exhibit very interesting features under tight focusing conditions, allowing, for instance, for the reduction of the focal spot size [12-14]. In a recent experimental and theoretical study, we took advantage of the phase relation between longitudinal and transverse electric field components in the focal plane of tightly focused radially polarized light to realize nanoparticle-mediated directional coupling into waveguides, a so-called nanobeacon [15].

In addition, we have also demonstrated other fascinating field distributions created by tight focusing of a specially polarized light beam exhibiting spin or orbital angular momenta. If, for instance, a lens is illuminated with a light beam, which is laterally split into two segments, one being left-handed the other one right-handed circularly polarized, a focal spot with a complex field and angular momentum density distribution is created. The focal spot appears deformed. In this configuration, a vectorial state of the light field with purely transverse angular momentum, a photonic wheel, is generated (see Fig.) [16]. Such an unusual light field finds application in optical tweezers and trapping systems. A particle trapped in a photonic wheel should spin around a transverse axis parallel to the purely transverse angular momentum providing additional rotational degree of freedom to single beam tweezers systems.
Furthermore, the observed deformation of the focal spot and the accompanying shift of its barycenter are intimately linked to the appearance of a beam-shift phenomenon discovered recently (see publications of the OTG group). This beam-shift effect, the so-called geometric spin Hall effect of light (gSHEL), and related phenomena are also studied in more detail in our group [17] and in collaboration with the groups QIV and OTG at MPL ([18,19] and others).

References:

  1. S. Quabis, R. Dorn and G. Leuchs, 
Generation of a radially polarized beam of high quality,
 Appl. Phys. B, 81 (5), 597-600 (2006)
  2. Y. Z. Ma, Y. Sych, G. Onishchukov, S. Ramachandran, U. Peschel, B. Schmauss and G. Leuchs,
 Fiber-modes and fiber-anisotropy characterization using low-coherence interferometry,
 Appl. Phys. B, 96 (2-3), 345-353 (2009)
  3. T. G. Euser, M. A. Schmidt, N. Y. Joly, C. Gabriel, C. Marquardt, L. Y. Zang, M. Förtsch, P. Banzer, A. Brenn, D. Elser, M. Scharrer, G. Leuchs, and P. St. J. Russell,
 Birefringence and dispersion of cylindrically polarized modes in nanobore photonic crystal fiber,
 Journal of the OSA B 21, Iss.1, pp. 193-198 (2011)
  4. S. Orlov and U. Peschel,
 Complex source beam: A tool to describe highly focused vector beams analytically,
 PRA 82, 063820-1-10 (2010)
  5. S. Orlov and P. Banzer,
 Vectorial complex-source vortex beams, 
Phys. Rev. A 90, 023832 (2014)
  6. S. Orlov, U. Peschel, T. Bauer, P. Banzer,
 Analytical expansion of highly focused vector beams into vector spherical harmonics and its application to Mie scattering,
 PRA 85, No. 6,063825 (2012)
  7. S. Quabis, R. Dorn, O. Glöckl, M. Eberler and G. Leuchs,
 The focus of light - theoretical calculation and experimental tomographic reconstruction,
 Appl. Phys. B, 71, 1-5 (2000)
  8. P. Marchenko, S. Orlov, C. Huber, P. Banzer, S. Quabis, U. Peschel, and G. Leuchs, Interaction of highly focused vector beams with a metal knife-edge,
 Optics Express 19, No. 8, pp. 7244-7261 (2011)
  9. C. Huber, S. Orlov, P. Banzer, and G. Leuchs,
 Corrections to the knife-edge based reconstruction scheme of tightly focused light beams, 
Optics Express 21, Iss. 21, pp. 25069-25076 (2013)
  10. T. Bauer, S. Orlov, U. Peschel, P. Banzer and G. Leuchs,
 Nanointerferometric amplitude and phase reconstruction of tightly focused vector beams,
 Nature Photonics 8, 23 - 27 (2014)
  11. R. Dorn, S. Quabis and G. Leuchs,
 The focus of light - llinear polarization breaks the rotational symmetry of the focal spot,
 J. Mod. Opt., 50 (12), 1917-1926 (2003)
  12. S. Quabis, R. Dorn, O. Glöckl, M. Reichle and M. Eberler,
 Reduction of the spot size by using a radially polarized laser beam,
 Proc. SPIE 4429, 105, (2000)
  13. S. Quabis, R. Dorn, M. Eberler, O. Glöckl and G. Leuchs, 
Focusing light to a tighter spot,
 Opt. Comm., 179, 1-7 (2000)
  14. R. Dorn, S. Quabis and G. Leuchs,
 Sharper Focus for a radially polarized light beam, Phys. Rev. Lett., 91 (23), 233901 (2003)
  15. M. Neugebauer, T. Bauer, P. Banzer and G. Leuchs,
 Polarization Tailored Light Driven Directional Optical Nanobeacon, 
Nano Letters 14, 2546 - 2551 (2014)
  16. P. Banzer, M. Neugebauer, A. Aiello, C. Marquardt, N. Lindlein, T. Bauer, G. Leuchs,
 The photonic wheel - demonstration of a state of light with purely transverse angular momentum,
 J. Europ. Opt. Soc. Rap. Public. 8, 13032 (2013)
  17. M. Neugebauer, P. Banzer, T. Bauer, S. Orlov, N. Lindlein, A. Aiello, and G. Leuchs, Geometric spin Hall effect of light in tightly focused polarization tailored light beams, Phys. Rev. A 89, No. 1, 013840 (2014)
  18. J. Korger, A. Aiello, C. Gabriel, P. Banzer, T. Kolb, Ch. Marquardt, G. Leuchs,
 Geometric spin Hall effect of light at polarizing interfaces,
 Appl. Phys. B 102 Iss. 3, p. 427 (2011)
  19. J. Korger, A. Aiello, V. Chille, P. Banzer, C. Wittmann, N. Lindlein, Ch. Marquardt and G. Leuchs, 
Observation of the geometric spin Hall effect of light,
 Phys. Rev. Lett. 112, 113902 (2014)

Optical Investigation of Single Sub-wavelength Nanostructures -
Polarization Tailored Light Fields as a Versatile Tool for Nanooptics

Keywords: Nanoplasmonics, nanostructures, SRRs, nanoparticles, nanoscopic waveguides

Light beams with unconventional and inhomogeneous field distributions, such as radially and azimuthally polarized cylindrical vector-beams or more complex configurations, can exhibit fascinating properties as described above. In addition, they also offer unique possibilities for studying light matter interaction at the nanoscale. Due to the customizable spatial field distribution, resonances or modes of a system under study can be excited and investigated selectively which are not accessible via plane wave illumination. For instance, we utilized such tightly focused cylindrical vector beams to study the waveguide properties of single circular hollow or coaxial apertures in sub-wavelength thin metal films [1,2]. Choosing tightly focused radially and azimuthally polarized light beams for these studies and, therefore, adapting the symmetry of the excitation mode to that of the nanoaperture enabled us to couple to corresponding waveguide modes.
For the study of more complex nanoscopic systems, we designed and built highly versatile and flexible experimental tools and setups and developed more sophisticated measurement techniques [3]. The sub-wavelength dimensions of the systems under study as well as the spatially varying electric and magnetic field distributions utilized as excitation allow for the realization of a manifold of different coupling scenarios within a single beam configuration (selective excitation of resonances) just depending on the location of the nanostructure relative to the beam. In the group, we have proven the versatility and applicability of this concept by performing detailed full spectral analyses of different model systems, e.g. individual sub-wavelength sized split-ring resonators [3], also revealing the electric and magnetic contributions to their resonances. We also study other types of nanostructures, which exhibit intriguing and exotic properties, such as chirality. In addition, the interaction of individual nanostructures with complex field distributions is also studied both numerically and analytically [4].
The abovementioned experimental setups and techniques constitute the foundation of the group’s recent experimental research and also find application in projects and labs of collaborators (see for instance [5,6]).

References:

  1. J. Müller, P. Banzer, S. Quabis, U. Peschel and G. Leuchs,
 Waveguide properties of single subwavelength holes demonstrated with radially and azimuthally polarized light,
Applied Physics B, 89 (4), 517-520 (2007)
  2. P. Banzer, J. Kindler, S. Quabis, U. Peschel and G. Leuchs,
 Extraordinary transmission through a single coaxial aperture in a thin metal film, Optics Express 18, No. 10, pp. 10896-10904 (2010)
  3. P. Banzer, U. Peschel, S. Quabis and G. Leuchs,
 On the experimental investigation of the electric and magnetic response of a single nano-structure,
 Optics Express 18, No. 10, pp. 10905–10923 (2010)
  4. S. Orlov, U. Peschel, T. Bauer, P. Banzer,
Analytical expansion of highly focused vector beams into vector spherical harmonics and its application to Mie scattering,
PRA 85, No. 6,063825 (2012)
  5. J. Wen, P. Banzer, A. Kriesch, D. Ploss, B. Schmauss, and U. Peschel, Experimental cross-polarization detection of coupling far-field light to highly confined plasmonic gap modes via nanoantennas, 
Appl. Phys. Lett. 98, 101109 (2011)
  6. A. Kriesch, S. Burgos, D. Ploss, H. Pfeifer, H. Atwater, U. Peschel, Functional Plasmonic Nanocircuits with Low Insertion and Propagation Losses, Nano Letters 13, pp. 4539-4545 (2013) and others

Nanostructure Ensembles and Metamaterials -
Optical Investigation and Advanced Nanofabrication

Keywords: Pick-and-place handling, nanoparticle ensembles, metamaterial

Beside the study of single nanoscopic particles and structures, we also investigate complex particle ensembles and metamaterials. As an example, we studied a simple metasurface consisting of a patterned ultra-thin metal film and its application as a mask in optical lithography (in collaboration with the group NONA and the Fraunhofer Institute for Integrated Systems). The structure acts as an array of antennas for the impinging light. Transmitted and forward scattered light will interfere destructively, for appropriately chosen geometrical parameters. The transmission is drastically reduced [1]. In another study (performed in the TDSU Photonic Nanostructures at MPL), we investigated the Raman enhancement in single-layered graphene mediated by a metallic nanostructure (split-ring resonator) array [2].
For fabrication, standard electron-beam litography or focused ion-beam milling is usually used. In this context, there is currently a general lack of methods to assemble individual nanoparticles into dedicated patterns. Many methods, such as self-assembly, do neither provide the desired fine control over the exact geometric configuration nor the capability of assembling heterogeneous patterns from different nanoparticles in a controlled and reliable fashion.
Therefore, we develop (in collaboration with the TDSU Photonic Nanostructures at MPL) a pick-and-place setup for controlled manipulation of nano-objects inside a scanning electron microscope (SEM) [3]. The manipulation process, utilizing AFM technology, can be visually controlled with the SEM in real-time. This permits assembling particles into desired patterns with high accuracy. The resulting complex nanoparticle ensembles exhibit extraordinary optical properties, which we investigate with tightly focused light beams using the group’s expertise in polarization tailoring.

References:

  1. S. Dobmann, D. Shyroki, P. Banzer, A. Erdmann, U. Peschel,
 Resonant metamaterials for contrast enhancement in optical lithography,
 Optics Express 20, No. 18, pp. 19928-19935 (2012)
  2. G. Sarau, B. Lahiri, P. Banzer, P. Gupta, A. Bhattacharya, F. Vollmer, S. Christiansen, Enhanced Raman Scattering of Graphene using Arrays of Split Ring Resonators, Advanced Optical Materials 1, Iss. 2, pp. 151–157 (2013)
  3. U. Mick, P. Banzer, S. Christiansen, and G. Leuchs, AFM-Based Pick-and-Place Handling of Individual Nanoparticles inside an SEM for the Fabrication of Plasmonic Nano-Patterns, in CLEO: 2014, OSA Technical Digest (online) (Optical Society of America, 2014), paper STu1H.1 and references therein


Further research activities and corresponding articles can be found in our full list of publications ->