Binocular adaptive optics vision analyzer with full control over the complex pupil functions

Author(s): Christina Schwarz, Pedro M. Prieto, Enrique J. Fernández, and Pablo Artal

Abstract:

“We present a binocular adaptive optics vision analyzer fully capable of controlling both amplitude and phase of the two complex pupil functions in each eye of the subject. A special feature of the instrument is its comparatively simple setup. A single reflective liquid crystal on silicon spatial light modulator working in pure phase modulation generates the phase profiles for both pupils simultaneously. In addition, another liquid crystal spatial light modulator working in transmission operates in pure intensity modulation to produce a large variety of pupil masks for each eye. Subjects perform visual tasks through any predefined variations of the complex pupil function for both eyes. As an example of the system efficiency, we recorded images of the stimuli through the system as they were projected at the subject’s retina. This instrument proves to be extremely versatile for designing and testing novel ophthalmic elements and simulating visual outcomes, as well as for further research of binocular vision.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 24, pp. 4779-4781 (2011)
doi:10.1364/OL.36.004779

Fabrication of microscale medical devices by two-photon polymerization with multiple foci via a spatial light modulator

Author(s): Shaun D. Gittard, Alexander Nguyen, Kotaro Obata, Anastasia Koroleva, Roger J. Narayan, and Boris N. Chichkov.

Abstract:

“Two-photon polymerization is an appealing technique for producing microscale devices due to its flexibility in producing structures with a wide range of geometries as well as its compatibility with materials suitable for biomedical applications. The greatest limiting factor in widespread use of two-photon polymerization is the slow fabrication times associated with line-by-line, high-resolution structuring. In this study, a recently developed technology was used to produce microstructures by two-photon polymerization with multiple foci, which significantly reduces the production time. Computer generated hologram pattern technology was used to generate multiple laser beams in controlled positions from a single laser. These multiple beams were then used to simultaneously produce multiple microstructures by two-photon polymerization. Arrays of micro-Venus structures, tissue engineering scaffolds, and microneedle arrays were produced by multifocus two-photon polymerization. To our knowledge, this work is the first demonstration of multifocus two-photon polymerization technology for production of a functional medical device. Multibeam fabrication has the potential to greatly improve the efficiency of two-photon polymerization production of microscale devices such as tissue engineering scaffolds and microneedle arrays.”

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Publication: Biomedical Optics Express, (free download)

Issue/Year/DOI: Biomedical Optics Express, Vol. 2, Issue 11, pp. 3167-3178 (2011)
doi:10.1364/BOE.2.003167

Photo-designed terahertz devices

Author(s): Takanori Okada & Koichiro Tanaka

Abstract:

“Technologies are being developed to manipulate electromagnetic waves using artificially structured materials such as photonic crystals and metamaterials, with the goal of creating primary optical devices. For example, artificial metallic periodic structures show potential for the construction of devices operating in the terahertz frequency regime. Here we demonstrate the fabrication of photo-designed terahertz devices that enable the real-time, wide-range frequency modulation of terahertz electromagnetic waves. These devices are comprised of a photo-induced, planar periodic-conductive structure formed by the irradiation of a silicon surface using a spatially modulated, femtosecond optical pulsed laser. We also show that the modulation frequency can be tuned by the structural periodicity, but is hardly affected by the excitation power of the optical pump pulse. We expect that our findings will pave the way for the construction of all-optical compact operating devices, such as optical integrated circuits, thereby eliminating the need for materials fabrication processes.”

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Publication: Scientific Reports, (free download)

Issue/Year/DOI: Scientific Reports, Volume 1, Article number:121, (2011)
doi:10.1038/srep00121

Positional stability of holographic optical traps

Author(s): Arnau Farré, Marjan Shayegan, Carol López-Quesada, Gerhard A. Blab, Mario Montes-Usategui, Nancy R. Forde, and Estela Martín-Badosa

Abstract:

“The potential of digital holography for complex manipulation of micron-sized particles with optical tweezers has been clearly demonstrated. By contrast, its use in quantitative experiments has been rather limited, partly due to fluctuations introduced by the spatial light modulator (SLM) that displays the kinoforms. This is an important issue when high temporal or spatial stability is a concern. We have investigated the performance of both an analog-addressed and a digitally-addressed SLM, measuring the phase fluctuations of the modulated beam and evaluating the resulting positional stability of a holographic trap. We show that, despite imparting a more unstable modulation to the wavefront, our digitally-addressed SLM generates optical traps in the sample plane stable enough for most applications. We further show that traps produced by the analog-addressed SLM exhibit a superior pointing stability, better than 1 nm, which is comparable to that of non-holographic tweezers. These results suggest a means to implement precision force measurement experiments with holographic optical tweezers (HOTs).”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 19, Issue 22, pp. 21370-21384 (2011)
doi:10.1364/OE.19.021370

Coaxial holographic encoding based on pure phase modulation

Author(s): Wei Jia, Zhongyu Chen, Fung Jacky Wen, Changhe Zhou, Yuk Tak Chow, and Po Sheun Chung

Abstract:

“We describe a simple technique for coaxial holographic image recording and reconstruction, employing a spatial light modulator (SLM) modified in pure phase mode. In the image encoding system, both the reference beam in the outside part and the signal beam in the inside part are displayed by an SLM based on the twisted nematic LCD. For a binary image, the part with amplitude of “1” is modulated with random phase, while the part with amplitude of “0” is modulated with constant phase. After blocking the dc component of the spatial frequencies, a Fourier transform (FT) hologram is recorded with a uniform intensity distribution. The amplitude image is reconstructed by illuminating the reference beam onto the hologram, which is much simpler than existing phase modulated FT holography techniques. The technique of coaxial holographic image encoding and recovering with pure phase modulation is demonstrated theoretically and experimentally in this paper. As the holograms are recorded without the high-intensity dc component, the storage density with volume medium may be increased with the increase of dynamic range. Such a simple modulation method will have potential applications in areas such as holographic encryption and high-density disk storage systems.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 50, Issue 34, pp. H10-H15 (2011)
doi:10.1364/AO.50.000H10

Closed-loop adaptive optics with a single element for wavefront sensing and correction

Author(s): Raúl Martínez-Cuenca, Vicente Durán, Justo Arines, Jorge Ares, Zbigniew Jaroszewicz, Salvador Bará, Lluís Martínez-León, and Jesús Lancis

Abstract:

“We propose a closed-loop adaptive optical arrangement based on a single spatial light modulator that simultaneously works as a correction unit and as the key element of a wavefront sensor. This is possible by using a liquid crystal on silicon display whose active area is divided into two halves that are respectively programmed for sensing and correction. We analyze the performance of this architecture to implement an adaptive optical system. Results showing a closed-loop operation are reported, as well as a proof of concept for dealing with aberrations comparable to those typically found in human eyes.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 18, pp. 3702-3704 (2011)
doi:10.1364/OL.36.003702

Controlling ghost traps in holographic optical tweezers

Author(s): Christina Hesseling, Mike Woerdemann, Andreas Hermerschmidt, Cornelia Denz.

Abstract:

“Computer-generated holograms displayed by phase-modulating spatial light modulators have become a well- established tool for beam shaping purposes in holographic optical tweezers. Still, the generation of light intensity patterns with high spatial symmetry and simultaneously without interfering ghost traps is a challenge. We have implemented an iterative Fourier transform algorithm that is capable of controlling these ghost traps and demonstrate the benefit of this approach in the experiment.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 18, pp. 3657-3659 (2011)
doi:10.1364/OL.36.003657

Wavefield imaging via iterative retrieval based on phase modulation diversity

Author(s): José A. Rodrigo, Tatiana Alieva, Gabriel Cristóbal, and María L. Calvo

Abstract:

“We present a fast and robust non-interferomentric wavefield retrieval approach suitable for imaging of both amplitude and phase distributions of scalar coherent beams. It is based on the diversity of the intensity measurements obtained under controlled astigmatism and it can be easily implemented in standard imaging systems. Its application for imaging in microscopy is experimentally studied. Relevant examples illustrate the approach capabilities for image super-resolution, numerical refocusing, quantitative imaging and phase mapping.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 19, Issue 19, pp. 18621-18635 (2011)
doi:10.1364/OE.19.018621

Intracavity vortex beam generation

Author(s): Darryl Naidoo, Andrew Forbes, Kamel Aït-Ameur

Abstract:

“In this paper we explore vortex beams and in particular the generation of single LG0l modes and superpositions thereof. Vortex beams carry orbital angular momentum (OAM) and this intrinsic property makes them prevalent in transferring this OAM to matter and to be used in quantum information processing. We explore an extra-cavity and intra-cavity approach in LG0l mode generation respectively. The outputs of a Porro-prism resonator are represented by “petals” and we show that through a full modal decomposition, the “petal” fields are a superposition of two LG0l modes.”

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Publication: SPIE Proceedings, (subscription required)

Issue/Year/DOI: Proc. SPIE, Volume 8130, 813009 (2011)
doi:10.1117/12.902330

Poynting vector and orbital angular momentum density of superpositions of Bessel beams

Author(s): Igor A. Litvin, Angela Dudley, and Andrew Forbes

Abstract:

“We study theoretically the orbital angular momentum (OAM) density in arbitrary scalar optical fields, and outline a simple approach using only a spatial light modulator to measure this density. We demonstrate the theory in the laboratory by creating superpositions of non-diffracting Bessel beams with digital holograms, and find that the OAM distribution in the superposition field matches the predicted values. Knowledge of the OAM distribution has relevance in optical trapping and tweezing, and quantum information processing.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 19, Issue 18, pp. 16760-16771 (2011)
doi:10.1364/OE.19.016760

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