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

The very long range nature of capillary interactions in liquid films

Author(s): Di Leonardo R, Saglimbeni F, Ruocco G.

Abstract:

“Micron-sized objects confined in thin liquid films interact through forces mediated by the deformed liquid-air interface. These capillary interactions provide a powerful driving mechanism for the self-assembly of ordered structures such as photonic materials or protein crystals. We demonstrate how optical micro-manipulation allows the direct measurement of capillary interactions between mesoscopic objects. The force falls off as an inverse power law in particles separation. We derive and validate an explicit expression for this exponent whose magnitude is mainly governed by particle size. For micron-sized objects we found an exponent close to, but smaller than 1, making capillary interactions a unique example of strong and very long ranged forces in the mesoscopic world.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett., Volume 100, Issue 10, 106103 (2008)
DOI: 10.1103/PhysRevLett.100.106103

Achromatic system for a twisted alignment liquid crystal wavefront corrector

Author(s): Zhaoliang Cao, Quanquan Mu, Lifa Hu, Yonggang Liu, Zenghui Peng, Xinghai Lu, and Li Xuan

Abstract:

“A twisted nematic liquid crystal wavefront corrector (TN-LCWFC) partially modulates the incident polarized light. A blazed grating may be preapplied on the TN-LCWFC to filter the unmodulated light for the purpose of stable adaptive correction. However, for broadband light, the dispersion of the blazed grating affects the image resolution. An achromatic method is presented to eliminate the dispersion of the blazed grating. Based on a prism model, we analyze the achromatic principle. An achromatic system with a conjugated blazed grating and an achromatic lens is given to eliminate the dispersion. An experiment was done with two transmitted blazed gratings so as to validate our method. Finally, a liquid crystal spatial light modulator was used as a conjugated grating to eliminate the dispersion of the blazed grating in an adaptive optics system. The results showed that the dispersion was partially compensated, and a resolvable image was achieved with a 600-700 nm wave band.”

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Publication:Applied Optics
Issue/Year: Applied Optics, Vol. 47, Issue 8, pp. 1020-1024 , 2008
DOI: 10.1364/AO.47.001020

High Closed Loop Correction Accuracy with a Liquid Crystal Wavefront Corrector

Author(s): Cao Zhao-Liang, Mu Quan-Quan, Hu Li-Fa, Liu Yong-Gang, Peng Zeng-Hui, Xuan Li

Abstract:

“We investigate the accurate control of a liquid crystal wavefront corrector. First, the Gamma correction technique is adopted to amend the nonlinear phase modulation. Then, the control method and wavefront reconstruction are considered. Lastly, a closed loop correction experiment is carried out and a high correction accuracy is obtained with peak to valley (PV) of 0.08λ (λ=632.8nm), the wavefront phase rms 0.015λ, as well as the Strehl ratio of 0.99. The diffraction-limited resolution is achieved.”

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Publication: Chinese Physics Letters
Issue/Year: Chinese Physics Letters 2008, Volume 25, Issue 3: 989-992
DOI: 10.1088/0256-307X/25/3/050

Laser beam shaping for micromaterial processing using a liquid crystal display

Author(s): U. Klug, M. Boyle, F. Friederich, R. Kling, and A. Ostendorf

Abstract:

“The high demand for beam shaping technology by the display industry has lead to higher resolutions, smaller pixel pitch and reduced costs. Nowadays high quality, nematic Liquid Crystal on Silicon microdisplays (LCoS) with resolutions of 1920 × 1080 pixels and 8 µm pixel pitch are available. The optical properties of these microdisplays allow for their application as an adaptive optical element where instantaneous change between arbitrary beam profiles is necessary. Laser material processing which often requires high beam qualities with various beam profiles is one industry where this technology could be applied. In this paper, a compact beam shaping setup and simple characterization methods for practical use of the LCoS at micromachining stations are presented. ”

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Publication: SPIE Digital Library
Issue/Year: Proc. SPIE, Vol. 6882, 688207 (2008)
DOI: 10.1117/12.763542

Near-perfect hologram reconstruction with a spatial light modulator

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

Abstract:

“We present an implementation method for noiseless holographic projection of precalculated light fields with a spatial light modulator. In the reconstructed image, both the spatial amplitude and phase distributions can be programmed independently. This is achieved by diffracting the light from two successive phase holograms that are located in conjugate Fourier planes. The light path is folded such that the two corresponding phase masks can be displayed side by side at a single phase-only spatial light modulator. Such a device has relevant applications in holographic display-or projection systems, and for optical micromanipulation in laser tweezers.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 4, pp. 2597-2603
DOI: 10.1364/OE.16.002597

Non-scanning motionless fluorescence three-dimensional holographic microscopy

Author(s): Joseph Rosen and Gary Brooker

Abstract:

“Holography is an attractive imaging technique as it offers the ability to view a complete three-dimensional volume from one image. However, holography is not widely applied to the field of three-dimensional fluorescence microscopic imaging, because fluorescence is incoherent and creating holograms requires a coherent interferometer system. Although scanning one beam of an interferometer pattern across the rear aperture of an objective to excite fluorescence in a specimen overcomes the coherence limitation, the mechanical scanning is complicated, which makes the image capturing slow, and the process is limited to low-numerical-aperture objectives. Here we present the first demonstration of a motionless microscopy system (FINCHSCOPE) based on Fresnel incoherent correlation holography, and its use in recording high-resolution three-dimensional fluorescent images of biological specimens. By using high-numerical-aperture objectives, a spatial light modulator, a CCD camera and some simple filters, FINCHSCOPE enables the acquisition of three-dimensional microscopic images without the need for scanning.”

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Publication: Nature Photonics
Issue/Year: Nature Photonics 2, 190 – 195 (2008)
DOI: 10.1038/nphoton.2007.300
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