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

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.”

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

Optically driven pumps and flow sensors for microfluidic systems

Author(s): H Mushfique, J Leach, R Di Leonardo, M J Padgett, J M Cooper

Abstract:

“This paper describes techniques for generating and measuring fluid flow in microfluidic devices. The first technique is for the multi-point measurement of fluid flow in microscopic geometries. The flow sensing method uses an array of optically trapped microprobe sensors to map out the fluid flow. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles’ displacements are monitored by digital video microscopy and directly converted into velocity field values. The second is a method for generating flow within a microfluidic channel using an optically driven pump. The optically driven pump consists of two counter-rotating birefringent vaterite particles trapped within a microfluidic channel and driven using optical tweezers. The transfer of spin angular momentum from a circularly polarized laser beam causes the particles to rotate at up to 10 Hz. The pump is shown to be able to displace fluid in microchannels, with flow rates of up to 200 m-3 s-1 (200 fL s-1). In addition a flow sensing method, based upon the technique mentioned above, is incorporated into the system in order to map the magnitude and direction of fluid flow within the channel.”

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Publication: Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science
Issue/Year: Journal of Mechanical Engineering Science, Volume 222, Number 5 / 2008, Pages 829-837
DOI: 10.1243/09544062JMES760

Improved micro topography measurement by LCoS-based fringe projection and z-stitching

Author(s): X. Schwab, C. Kohler, K. Körner, N. Eichhorn, W. Osten

Abstract:

“Fringe projection is a commonly used method for 3D surface metrology. Numerous applications have demonstrated a measurement field from a few millimeters to several meters. To enable the measurement of micro systems with this method, a zoom stereo microscope from Leica was used as the basis for the implementation of a fringe projection microscope. A state of the art twisted nematic WUXGA LCD was used for flexible fringe generation. The high fill factor of this reflective LCoS in combination with a 500 Lumen LED and a 12 bit CCD camera delivers fringe patterns with high contrast. This allows us to measure objects with both a strong reflectivity variation and a low reflectivity. The second main objective was to increase the measurement field and the depth of field. Using the zoom system and exchangeable microscope objectives, the measurement fields could be changed quickly from 4 cm² to less than 1 mm². Depending on the measurement field, the depth of field was between 5.22 mm and 0.018 mm. However, this was often not sufficient to measure the complete depth of a 3D-object. The microscope system also features an integrated high precision motor stage, which is already used for system calibration. Based on this, we implemented a new z-stitching method where n measurements at different well determined z-positions of the motor stage were performed. The n resulting topography maps can be stitched together to get the complete depth map of the entire object. Thus the depth measurement range is only limited by the mechanics of the z-stage. ”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6995, 69950Q (2008);
DOI: 10.1117/12.781822

Spatial amplitude and phase modulation using commercial twisted nematic LCDs

Author(s): E. G. van Putten, I. M. Vellekoop, and A. P. Mosk

Abstract:

“We present a method for full spatial phase and amplitude control of a laser beam using a twisted nematic LCD combined with a spatial filter. By spatial filtering we combine four neighboring pixels into one superpixel. At each superpixel we are able to independently modulate the phase and the amplitude of light. We experimentally demonstrate the independent phase and amplitude modulation using this novel technique. Our technique does not impose special requirements on the spatial light modulator and allows precise control of fields even with imperfect modulators.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 47, Issue 12, pp. 2076-2081, 2008
DOI: 10.1364/AO.47.002076

Spectral and temporal response of liquid-crystal-on-silicon spatial light modulators

Author(s): Martin Bock, Susanta Kumar Das, Ruediger Grunwald, Stefan Osten, Peter Staudt and Gero Stibenz

Abstract:

“Spectral and temporal phase response of selected types of liquid-crystal-on-silicon spatial light modulators were studied using femtosecond pulses, determining specific transfer functions of the devices. The phase response resulting from programed gray level distributions was detected by analyzing the diffraction characteristics and by spectral phase interferometry for direct electric-field reconstruction. The results indicate the appearance of distinct parameter ranges that enable minimum spatiotemporal distortion. Weak oscillations in the spectral phase are explained by Gires–Tournois resonances [F. Gires and P. Tournois, Acad. Sci. Paris, C. R. 258, 6112 (1964)].”

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Publication: Applied Physics Letters
Issue/Year: Appl. Phys. Lett. 92, 151105 (2008)
DOI: 10.1063/1.2909115

Optical tweezers of programmable shape with transverse scattering forces

Author(s): Alexander Jesacher, Christian Maurer, Severin Fuerhapter, Andreas Schwaighofer, Stefan Bernet, Monika Ritsch-Marte

Abstract:

“We propose a non-holographic method to create line traps of arbitrary shape in the sample plane. Setting the phase gradient along theses lines gives control over the transverse forces acting on the confined particles. Phase structures, displayed on a spatial light modulator, are optically processed by a spiral phase filter and imaged onto the object plane of a microscope objective. The resulting bright line structures can be used to trap microparticles. Additionally, they exert transverse scattering forces, which can be exploited for inducing orbital motions or for creating “attracting” or “repelling” points, respectively. We give theoretical and experimental evidence that these scattering forces are proportional to the curvature of the line tweezers.”

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Publication:Optics Communications
Issue/Year: Optics Communications, Volume 281, Issue 8, 15 April 2008, Pages 2207-2212
DOI: 10.1016/j.optcom.2007.12.042

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

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.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 8, pp. 5164-5170, 2008
DOI: 10.1364/OE.16.005164

Full phase and amplitude control of holographic optical tweezers with high efficiency

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

Abstract:

“Recently we demonstrated the applicability of a holographic method for shaping complex wavefronts to spatial light modulator (SLM) systems. Here we examine the potential of this approach for optical micromanipulation. Since the method allows one to shape both amplitude and phase of a trapping light field independently and thus provides full control over scattering and gradient forces, it extends the possibilities of commonly used holographic tweezers systems. We utilize two cascaded phase-diffractive elements which can actually be display side-by-side on a single programmable phase modulator. Theoretically the obtainable light efficiency is close to 100%, in our case the major practical limitation arises from absorption in the SLM. We present data which demonstrate the ability to create user-defined “light pathways” for microparticles driven by transverse radiation pressure.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 7, pp. 4479-4486, 2008
DOI: 10.1364/OE.16.004479

Wavelength dependence of polarimetric and phase-shift characterization of a liquid crystal on silicon display

Author(s): A. Lizana, A. Marquez, I. Moreno, C. Iemmi, J. Campos, M.J. Yzuel

Abstract:

“We present a full characterization of a liquid-crystal-on-silicon (LCoS) display, including a polarimetric analysis based on the Mueller-Stokes formalism, and a phase shift modulation calibration. Results for different wavelengths are compared. The goal of this work is two fold. On one side, previous papers dealing with the illumination wavelength 633 nm have shown that LCoS produce a non negligible amount of depolarized light. This may have a negative impact in certain applications. Here we want to establish how this depolarization varies with the wavelength. On the other side, to use the LCoS as a spatial light modulator (SLM) we need to obtain optimal configurations enabling for phase-only or for amplitude-only modulation. Here we show how phase-only modulation is obtained, and how it evolves with the wavelength. In principle, for shorter wavelengths the phase modulation depth increases and the energy throughput may also be increased. However, these phase-only configurations may be partially degraded by the presence of depolarization at certain gray levels. Thus, the Mueller-Stokes formalism is necessary to get a full picture of the performance exhibited by the LCoS at each wavelength”

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Publication: Journal of the European Optical Society
Issue/Year: Journal of the European Optical Society, Vol 3 (2008)
DOI: 10.2971/jeos.2008.08012

Combined Mueller and Jones matrix method for the evaluation of the complex modulation in a liquid-crystal-on-silicon display

Author(s): I. Moreno, A. Lizana, J. Campos, A. Márquez, C. Iemmi, and M. J. Yzuel

Abstract:

“We apply the polar decomposition of the Mueller matrix describing a liquid-crystal-on-silicon display to identify the diattenuator, depolarizer, and retarder contributions as a function of the gray level. The retarder contribution is expressed in terms of the equivalent Jones matrix to apply previous techniques to evaluate the phase modulation. This allows searching for optimized polarization configurations for phase- or amplitude-only modulation responses. We present results for λ=633 nm showing a phase-only modulation up to 2π rad and flat intensity modulation.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 33, Issue 6, pp. 627-629, 2008
DOI: 10.1364/OL.33.000627
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