Spiral phase filtering and orientation-selective edge detection/enhancement

July, 2009

Author(s): Guohai Situ, Giancarlo Pedrini, Wolfgang Osten

Abstract:

“A spiral phase plate with an azimuthal structure exp[iϕ](0⩽ϕ<2π) has been used as a filter in a 4f system to achieve edge enhancement. Generally such edge-enhanced effect is isotropic, i.e., each edge of an input pattern is enhanced to the same degree regardless of its orientation. We found that one can achieve anisotropic edge enhancement by breaking down the symmetry of the filtering process. This can be done in two ways: first, by use of a fractional spiral phase filter (SPF) with a fractional topological charge and a controllable orientation of the edge discontinuity, and second, by the lateral shifting of the SPF. We interpret this process as a vortex formation due to the diffraction of the Fourier spectrum of the input pattern by a SPF with an integer and fractional topological charge. Optical experiments using a spatial light modulator were carried out to verify our proposal." Link to Publications Page

Publication: J. Opt. Soc. Am. A, (subscription required)

Issue/Year/DOI: JOSA A, Vol. 26, Issue 8, pp. 1788-1797 (2009)
doi:10.1364/JOSAA.26.001788


Model-free method for measuring the full Jones matrix of reflective liquid-crystal displays

April, 2009

Author(s): Christian Kohler, Tobias Haist, Wolfgang Osten

Abstract:

“We present a method for measuring all eight parameters (including the signs) of the Jones matrices of liquid-crystal displays. The method can be applied to measure the Jones matrices for all addressable gray levels thus delivering the specifications needed for calculating characteristic curves for arbitrary input and output polarizations. Unlike other approaches, we do not rely on a physical model of the LCD. Thus, it is possible to measure the Jones matrices of a more complex optical system in one step (e.g., when a reflective LCD is used in combination with a beamsplitter). Though the method presented is, in principle, applicable for transmissive and reflective LCDs, calculations and experiments are only shown using the example of a reflective liquid-crystal-on-silicon display. ”

Link to Publications Page

Publication: SPIE – Optical Engineering, (subscription required)

Issue/Year/DOI: SPIE – Optical Engineering, Vol. 48, 044002 (2009)
doi:10.1117/1.3119309


Phase contrast microscopy with full numerical aperture illumination

November, 2008

Author(s): Christian Maurer, Alexander Jesacher, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“A modification of the phase contrast method in microscopy is presented, which reduces inherent artifacts and improves the spatial resolution. In standard Zernike phase contrast microscopy the illumination is achieved through an annular ring aperture, and the phase filtering operation is performed by a corresponding phase ring in the back focal plane of the objective. The Zernike method increases the spatial resolution as compared to plane wave illumination, but it also produces artifacts, such as the halo- and the shade-off effect. Our modification consists in replacing the illumination ring by a set of point apertures which are randomly distributed over the whole aperture of the condenser, and in replacing the Zernike phase ring by a matched set of point-like phase shifters in the back focal plane of the objective. Experimentally this is done by illuminating the sample with light diffracted from a phase hologram displayed at a spatial light modulator (SLM). The subsequent filtering operation is then done with a second matched phase hologram displayed at another SLM in a Fourier plane of the imaging pathway. This method significantly reduces the haloand shade-off artifacts whilst providing the full spatial resolution of the microscope.”

Link to Publications Page

Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 16, Issue 24, pp. 19821-19829
doi:10.1364/OE.16.019821


Novel approaches to the design of halftone masks for analog lithography

September, 2008

Author(s): Marcel Teschke and Stefan Sinzinger

Abstract:

“We report novel approaches to the design of halftone masks for analog lithography. The approaches are derived from interferometric phase contrast. In a first step we show that the interferometric phase-contrast method with detour holograms can be reduced into a single binary mask. In a second step we introduce the interferometric phase-contrast method by interference of the object wavefront with the conjugate object wavefront. This method also allows for a design of a halftone mask. To use kinoform holograms as halftone phase masks, we show in a third step the combination of the zeroth-order phase-contrast technique with the interferometric phase-contrast method.”

Link to Publications Page

Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 47, Issue 26, pp. 4767-4776 (2008)
doi:10.1364/AO.47.004767


Hologram optimization for SLM-based reconstruction with regard to polarization effects

September, 2008

Author(s): C. Kohler, T. Haist, X. Schwab, and W. Osten

Abstract:

“We report on first results obtained with two modified hologram optimization algorithms. These algorithms take into account the complex modulation characteristic of the spatial light modulators employed for hologram reconstruction. To this end the Jones matrices of the modulator as well as all other components of the setup are used within a modified direct binary search and an iterative Fourier transform algorithm. Geometrical phase effects are included in the optimization. Elimination of the analyzer behind the spatial light modulator is possible by that approach and for typical setups using twisted-nematic liquid crystal modulators an enhanced overall diffraction efficiency is achieved. Possible applications are the comparative digital holography and optical tweezers. Experimental results for the reconstructions of holograms with a Holoeye LC-R 3000 modulator are presented.”

Link to Publications Page

Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 16, Issue 19, pp. 14853-14861 (2008)
doi:10.1364/OE.16.014853


Application of an interferometric phase contrast method to fabricate arbitrary diffractive optical elements

May, 2008

Author(s): Marcel Teschke, Robert Heyer, Marco Fritzsche, Sebastian Stoebenau, Stefan Sinzinger

Abstract:

“A novel approach for the fabrication of diffractive optical elements is described. This approach is based on an interferometric phase contrast method that transforms a complex object wavefront into an intensity pattern. The resulting intensity pattern is used to expose a photoresist layer on a substrate. After development, a diffractive phase object with an on-axis diffraction pattern is achieved. We show that the interferometric phase contrast method allows a precise control of the resulting intensity pattern. An array of blazed Fresnel lenses is realized in photoresist by using kinoform or detour-phase computer holograms for the interferometric phase contrast setup.”

Link to Publications Page

Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 47, Issue 14, pp. 2550-2556 (2008)
doi:10.1364/AO.47.002550


Two-dimensional photonic quasicrystals by single beam computer-generated holography

March, 2008

Author(s): Gianluigi Zito, Bruno Piccirillo, Enrico Santamato, Antigone Marino, Volodymyr Tkachenko, and Giancarlo Abbate

Abstract:

“Recently important efforts have been dedicated to the realization of a new kind of photonic crystals, known as photonic quasicrystals, in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. Here we show a novel approach to their fabrication based on the use of a programmable Spatial Light Modulator encoding Computer-Generated Holograms. Using this single beam technique we fabricated Penrose-tiled structures possessing rotational symmetry up to 23-fold, and a two-dimensional Thue-Morse structure, which is an aperiodic structure not achievable by multiple beam holography.”

Link to Publications Page

Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 16, Issue 8, pp. 5164-5170
doi:10.1364/OE.16.005164


Hypergeometric-Gaussian modes

October, 2007

Author(s): Ebrahim Karimi, Gianluigi Zito, Bruno Piccirillo, Lorenzo Marrucci, and Enrico Santamato

Abstract:

“We studied a novel family of paraxial laser beams forming an overcomplete yet nonorthogonal set of modes. These modes have a singular phase profile and are eigenfunctions of the photon orbital angular momentum. The intensity profile is characterized by a single brilliant ring with the singularity at its center, where the field amplitude vanishes. The complex amplitude is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric-Gaussian (HyGG) modes. Unlike the recently introduced hypergeometric modes [Opt. Lett. 32, 742 (2007)], the HyGG modes carry a finite power and have been generated in this work with a liquid-crystal spatial light modulator. We briefly consider some subfamilies of the HyGG modes as the modified Bessel Gaussian modes, the modified exponential Gaussian modes, and the modified Laguerre-Gaussian modes.”

Link to Publications Page

Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 32, Issue 21, pp. 3053-3055
doi:10.1364/OL.32.003053


Reverse orbiting of microparticles in optical vortices

October, 2006

Author(s): A. Jesacher, S. Fürhapter, C. Maurer, S. Bernet, and M. Ritsch-Marte

Abstract:

“We report the observation of particles trapped at an air-water surface orbiting in a reverse direction with respect to the orbital angular momentum of the light field. The effect is explained by a combination of asymmetric particle shape and confinement of the particle on the 2D air-water interface. The experiment highlights the strong influence of the particle shape on the momentum transfer, an effect that is often not considered in optical trapping experiments.”

Link to Publications Page

Publication: Optics Letters (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 31, Issue 19, pp. 2824-2826
doi:10.1364/OL.31.002824


Dynamisches System für die Aufnahme und optische Rekonstruktion von digitalen Hologrammen

June, 2006

Author(s): G. Wernicke, J. Frank, C. Günther, S. Krüger

Abstract:

“Es wird ein Aufbau zur Aufnahme und optischen Rekonstruktion von digitalen Hologrammen unter Verwendung von reflektiven Flüssigkristalldisplays vorgestellt. Anwendungen mit einer speziell modulierten Beleuchtung bei der Aufnahme zur Darstellung von holographischen Interferogrammen und die optische Rekonstruktion von Röntgenhologrammen wird gezeigt.”

Link to Publications Page

Publication: DGaO Proceedings, (free download)

ISSN: 1614-8436