Double peacock eye optical element for extended focal depth imaging with ophthalmic applications

April, 2012

Author(s): Lenny A. Romero, María S. Millán, Zbigniew Jaroszewicz, Andrzej Kolodziejczyk.

Abstract:

“The aged human eye is commonly affected by presbyopia, and therefore, it gradually loses its capability to form images of objects placed at different distances. Extended depth of focus (EDOF) imaging elements can overcome this inability, despite the introduction of a certain amount of aberration. This paper evaluates the EDOF imaging performance of the so-called peacock eye phase diffractive element, which focuses an incident plane wave into a segment of the optical axis and explores the element’s potential use for ophthalmic presbyopia compensation optics. Two designs of the element are analyzed: the single peacock eye, which produces one focal segment along the axis, and the double peacock eye, which is a spatially multiplexed element that produces two focal segments with partial overlapping along the axis. The performances of the peacock eye elements are compared with those of multifocal lenses through numerical simulations as well as optical experiments in the image space. The results demonstrate that the peacock eye elements form sharper images along the focal segment than the multifocal lenses and, therefore, are more suitable for presbyopia compensation. The extreme points of the depth of field in the object space, which represent the remote and the near object points, have been experimentally obtained for both the single and the double peacock eye optical elements. The double peacock eye element has better imaging quality for relatively short and intermediate distances than the single peacock eye, whereas the latter seems better for far distance vision.”

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Publication: Journal of Biomedical Optics , (subscription required)

Issue/Year/DOI: J. Biomed. Opt. 17, 046013 (Apr 27, 2012)
doi:10.1117/1.JBO.17.4.046013


Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination

March, 2012

Author(s): Antonio Ambrosio, Lorenzo Marrucci, Fabio Borbone, Antonio Roviello, Pasqualino Maddalena

Abstract:

“When an azobenzene-containing polymer film is exposed to a non-uniform illumination, a light-induced mass migration process may be induced, leading to the formation of relief patterns on the polymer free surface. Despite a research effort of many years and several proposed models many aspects of this phenomenon remain not well understood. Here we report the appearance of spiral-shaped relief patterns on the polymer under the illumination of focused Laguerre-Gauss beams, having helical wavefront and an optical vortex at their axis. The induced spiral reliefs are sensitive to the vortex topological charge and to the wavefront handedness. These findings are unexpected, because the “doughnut”-shaped intensity profile of Laguerre- Gauss beams contains no information about the wavefront handedness. We propose a model that explains the main features of this phenomenon from the surface-mediated interference of the longitudinal and the transverse components of the optical field. These results may find applications in optical micro- and nanolithography and optical-field. ”

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Publication: eprint arXiv:1203.5205, (free download)

Issue/Year/DOI: eprint arXiv:1203.5205 (2012)
Bibliographic Code: 2012arXiv1203.5205A


Three dimensional optical twisters-driven helically stacked multi-layered microrotors

March, 2012

Author(s): Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta

Abstract:

“We demonstrate tunable helically stacked multi-layered microrotors realized in vortex-embedded three dimensional (3D) optical twister patterns. Intensity-tunable annular irradiance profiles with higher order vortex are generated as well as simultaneously unfolded by phase-engineered multiple plane wave interference. In the individually tunable 3D helical bright arms of these unfolded vortex structures, 2 μm silica beads are optically trapped as spiraling multilayered handles of multi-armed microrotors. Further, multiple rows of such microrotors are parallelly actuated with controllable sense of rotation. We also present our observation on helical 3D stacking of micro-particles in these longitudinally gyrating multi-armed rotor traps.”

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Publication: Applied Physics Letters, (subscription required)

Issue/Year/DOI: Applied Physics Letters, Volume 100, Issue 12, (2012)
doi:10.1063/1.3693413


Vertical differential interference contrast

February, 2012

Author(s): Michael Warber, Tobias Haist, Malte Hasler, and Wolfgang Osten

Abstract:

“We propose a new phase contrast filtering technique based on a combination of a focused and a defocused point-spread-function. This way, an axial shear is introduced in the imaging system. Compared to conventional differential interference contrast, an isotropic behavior is achieved. The lateral resolution is improved compared to conventional defocusing. Furthermore, the digital combination of multiple images leads to strongly enhanced visualization of small structures. We show simulated results as well as experimental results using a spatial-light modulator-based microscope.”

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Publication: Optical Engineering, (subscription required)

Issue/Year/DOI: Opt. Eng., Volume 51, Issue 1, 013204, (2012)
doi:10.1117/1.OE.51.1.013204


Scattered light fluorescence microscopy in three dimensions

January, 2012

Author(s): Giulia Ghielmetti and Christof M. Aegerter

Abstract:

“Recently, we have proposed a method to image fluorescent structures behind turbid layers at diffraction limited resolution using wave-front shaping and the memory effect. However, this was limited to a raster scanning of the wave-front shaped focus to a two dimensional plane. In applications, it can however be of great importance to be able to scan a three dimensional volume. Here we show that this can be implemented in the same setup. This is achieved by the addition of a parabolic phase shift to the shaped wave-front. Via the memory effect, this phase shift leads to a shift of the interference based focus in the z-direction, thus opening the possibility of three dimensional imaging using scattered light fluorescence microscopy. Here, we show an example of such a three dimensional image of fluorescent nano-beads taken behind a turbid layer more than 10 mean free paths thick. Finally, we discuss the differences of the scanning in the z-direction with that in the x–y plane and the corresponding possibilities and limitations of the technique.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 20, Issue 4, pp. 3744-3752 (2012)
doi:10.1364/OE.20.003744


Positional stability of holographic optical traps

October, 2011

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


Controlling ghost traps in holographic optical tweezers

September, 2011

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


Intracavity vortex beam generation

August, 2011

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

August, 2011

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


Generation of an axially super-resolved quasi-spherical focal spot using an amplitude-modulated radially polarized beam

June, 2011

Author(s): Han Lin, Baohua Jia, and Min Gu

Abstract:

“An axially super-resolved quasi-spherical focal spot can be generated by focusing an amplitude-modulated radially polarized beam through a high numerical aperture objective. A method based on the unique depolarization pro perties of a circular focus is proposed to design the amplitude modulation. The generated focal spot shows a ratio of x∶y∶z=1∶1∶1.48 for the normalized FWHM in three dimensions, compared to that of x∶y∶z=1∶0.74∶1.72 under linear polarization (in the x direction) illumination. Moreover, the focusable light efficiency of the designed amplitude-modulated beam is 65%, which is more than 3 times higher than the optimized case under linear polarization and thus make the amplitude-modulated radial polarization beam more suitable for a wide range of applications.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 13, pp. 2471-2473 (2011)
doi:10.1364/OL.36.002471