Automated trapping, assembly, and sorting with holographic optical tweezers

Author(s): Stephen C. Chapin, Vincent Germain, and Eric R. Dufresne

Abstract:

“We combine real-time feature recognition with holographic optical tweezers to automatically trap, assemble, and sort micron-sized colloidal particles. Closed loop control will enable new applications of optical micromanipulation in biology, medicine, materials science, and possibly quantum computation.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 26, pp. 13095-13100 , 2006
DOI: 10.1364/OE.14.013095

Wavelet-modified fringe-adjusted joint transform correlator

Author(s): Alpana Bhagatji, Naveen K. Nishchal, and Arun K. Gupta, B. P. Tyagi

Abstract:

“In this paper, we implement a wavelet-modified fringe-adjusted joint transform correlator (JTC) for real-time target recognition applications. In real-time situation the input scene is captured using a CCD/thermal camera. The obtained joint power spectrum is multiplied with a pre-synthesized fringe-adjusted filter and the resultant function is processed with an appropriately scaled wavelet filter. The wavelet-modified fringe-adjusted JTC has been found to yield better results in comparison to the conventional fringe-adjusted JTC. To suppress the undesired strong dc, the resultant function is differentiated. Differential processing the wavelet-modified fringe-adjusted joint power spectrum removes the zero-order spectra and hence improves the detection efficiency. To focus the correlation terms in different planes in order to capture one of the desired autocorrelation peaks and discard the strong dc and another autocorrelation peak, chirp-encoding technique has also been applied. Computer simulation and experimental results are presented. ”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6405, 640513 (2006);
DOI: 10.1117/12.697891

A liquid crystal atmospheric turbulence simulator

Author(s): Lifa Hu, Li Xuan, Zhaoliang Cao, Quanquan Mu, Dayu Li, and Yonggang Liu

Abstract:

“In the paper, a method to calculate the time evolution turbulence wavefronts based on the covariance method is theoretically presented in detail. According to it, the time-evolution wavefronts disturbed by atmospheric turbulence were experimentally generated by our LC atmospheric turbulence simulator (ATS) based on liquid crystal on silicon (LCOS) with high pixel density, and measured with a wavefront sensor. The advantage of such a LC ATS over a conventional one is that it is flexible with considering the weather parameters of wind speed and Cn², and is relatively easy to control.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 25, pp. 11911-11918 (2006)
DOI: 10.1364/OE.14.011911

Direct measurement of the skew angle of the Poynting vector in a helically phased beam

Author(s): Jonathan Leach, Stephen Keen, Miles J. Padgett, Christopher Saunter, and Gordon D. Love

Abstract:

“We measure the local skew angle of the Poynting vector within a helically-phased, exp (il φ), beam using a Shack Hartmann wavefront sensor. It is the skew angle of the Poynting vector with respect to the beam axis that gives rise to the orbital angular momentum of a light beam. We confirm that this skew angle is l/kr, corresponding to an orbital angular momentum of lћ per photon. Measurement of orbital angular momentum in this way is an alternative to interferometric techniques giving a non-ambiguous result to both the magnitude and sign of l from a single measurement, without any restriction on the optical bandwidth.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 14, Issue 25, pp. 11919-11924 (2006)
DOI: 10.1364/OE.14.011919

Optimization of Liquid-Crystal Spatial Light Modulator for Precise Phase Generation

Author(s): Seow-Hwang Eng; Dong Mei Cai; Zhenglin Wang; Alameh, K.; Wenhan Jiang;

Abstract:

“Spatial light modulators (SLMs) are recently emerging as wavefront generation or reconstruction devices. In this paper, we use a liquid-crystal SLM (LC-SLM) as a wavefront generation device through the modulation of the spatial phase distribution of an incident light beam. We characterize the phase modulation performance of the LC-SLM, and identified a polarization-configuration to minimize its amplitude modulation effects in order to maximize the contrast of reconstructed phase holograms. We also investigated the feasibility of determining the optical surface uniformity of the LC-SLM through computations of the interference fringes, and identified the disadvantages of this method. This new approach may be used to determine the optical surface quality of other optical devices.”

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Publication: Conference on Optoelectronic and Microelectronic Materials and Devices
Issue/Year: Conference on Optoelectronic and Microelectronic Materials and Devices (2006)
DOI: 10.1109/COMMAD.2006.4429891

Digital speckle shearing interferometer using a liquid-crystal spatial light modulator

Author(s): Shuai Zhao and Po Sheun Chung

Abstract:

“A digital speckle shearing interferometer is developed using a dynamic binary phase grating realized by an electrically addressed, twisted nematic liquid-crystal spatial light modulator as the shearing element. The standard phase-shifting algorithm can be easily achieved by changing the grating pattern displayed on the spatial light modulator. The method has a number of advantages including variable sensitivity, no moving part, and no requirement for calibration of the value of the phase shift. The error due to the unexpected diffraction order is also discussed. ”

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Publication: SPIE – Optical Engineering
Issue/Year: SPIE – Optical Engineering, Vol. 45, 105606 (2006);
DOI: 10.1117/1.2360940

Reverse orbiting of microparticles in optical vortices

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.”

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

Diffraction-based determination of the phase modulation for general spatial light modulators

Author(s): David Engström, Gabriel Milewski, Jörgen Bengtsson, and Sheila Galt

Abstract:

“We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2π rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 45, Issue 28, pp. 7195-7204 (2006)
DOI: 10.1364/AO.45.007195

Algorithm for computing holographic optical tweezers at video rates

Author(s): Mario Montes-Usategui, Encarnación Pleguezuelos, Jordi Andilla, Estela Martín-Badosa, and Ignacio Juvells

Abstract:

“Digital holography enables the creation of multiple optical traps at arbitrary three-dimensional locations and spatial light modulators permit updating those holograms at video rates. However, the time required for computing the holograms makes interactive optical manipulation of several samples difficult to achieve. We introduce an algorithm for computing holographic optical tweezers that is both easy to implement and capable of speeds in excess of 10 Hz when running on a Pentium IV computer. A discussion of the pros and cons of the algorithm, a mathematical analysis of the efficiency of the resulting traps, as well as results of the three-dimensional manipulation of polystyrene micro spheres are included.”

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Publication: SPIE Digital Library
Issue/Year: Proceedings Volume 6326, Optical Trapping and Optical Micromanipulation III; 63262X (2006)
DOI: 10.1117/12.680504

Design of a low-cost interactive holographic optical tweezers system

Author(s): E. Pleguezuelos, J. Andilla, A. Carnicer, E. Martín-Badosa, S. Vallmitjana, and M. Montes-Usategui.

Abstract:

“The paper describes the design of an inexpensive holographic optical tweezers setup. The setup is accompanied by software that allows real-time manipulation of the sample and takes into account the experimental features of the setup, such as aberration correction and LCD modulation. The LCD, a HoloEye LCR-2500, is the physical support of the holograms, which are calculated using the fast random binary mask algorithm. The real-time software achieves 12 fps at full LCD resolution (including aberration correction and modulation) when run on a Pentium IV HT, 3.2 GHz computer.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE 6326, 63262Q (2006)
DOI: 10.1117/12.680593
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