Fast parallel diffractive multi-beam femtosecond laser surface micro-structuring

Author(s): Zheng Kuang, Dun Liu, Walter Perrie, Stuart Edwardson, Martin Sharp, Eamonn Fearon, Geoff Dearden, Ken Watkins

Abstract:

“Fast parallel femtosecond laser surface micro-structuring is demonstrated using a spatial light modulator (SLM). The Gratings and Lenses algorithm, which is simple and computationally fast, is used to calculate computer generated holograms (CGHs) producing diffractive multiple beams for the parallel processing. The results show that the finite laser bandwidth can significantly alter the intensity distribution of diffracted beams at higher angles resulting in elongated hole shapes. In addition, by synchronisation of applied CGHs and the scanning system, true 3D micro-structures are created on Ti6Al4V.”

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Publication: Applied Surface Science
Issue/Year: Applied Surface Science, Volume 255, Issues 13-14, 15 April 2009, Pages 6582-6588
DOI: 10.1016/j.apsusc.2009.02.043

Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor

Author(s): Carol López-Quesada, Jordi Andilla, Estela Martín-Badosa

Abstract:

“Optical aberration due to the nonflatness of spatial light modulators used in holographic optical tweezers significantly deteriorates the quality of the trap and may easily prevent stable trapping of particles. We use a Shack-Hartmann sensor to measure the distorted wavefront at the modulator plane; the conjugate of this wavefront is then added to the holograms written into the display to counteract its own curvature and thus compensate the optical aberration of the system. For a Holoeye LC-R 2500 reflective device, flatness is improved from 0.8λ to λ/16 (λ=532 nm), leading to a diffraction-limited spot at the focal plane of the microscope objective, which makes stable trapping possible. This process could be fully automated in a closed-loop configuration and would eventually allow other sources of aberration in the optical setup to be corrected for.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 48, Issue 6, pp. 1084-1090 (2009)
DOI: 10.1364/AO.48.001084

Systematic errors of an optical encryption system due to the discrete values of a spatial light modulator

Author(s): David S. Monaghan, Unnikrishnan Gopinathan, Damien P. Kelly, Thomas J. Naughton, John T. Sheridan

Abstract:

“An optical implementation of the amplitude encoded double random phase encryption/decryption technique is implemented, and both numerical and experimental results are presented. In particular, we examine the effect of quantization in the decryption process due to the discrete values and quantized levels, which a spatial light modulator (SLM) can physically display. To do this, we characterize a transmissive SLM using Jones matrices and then map a complex image to the physically achievable levels of the SLM using the pseudorandom encoding technique. We present both numerical and experimental results that quantify the performance of the system. ”

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Publication: SPIE – Optical Engineering
Issue/Year: Opt. Eng., Vol. 48, 027001 (2009);
DOI: 10.1117/1.3076208

Phase Contrast Projection Display Using Photopolymer

Author(s): Piao, Mei-Lan; Kim, Nam; Park, Jae-Hyeung

Abstract:

“We propose a phase contrast filter using photopolymer, for the phase contrast projection display. The photopolymer has high photosensitivity such that its optically induced refractive index change has a linear dependency on the illuminating light intensity. We implemented a phase contrast projection display using photopolymer as a phase contrast filter. By controlling the refractive index change of the photopolymer, we successfully convert an input phase image into a high contrast intensity image. We also investigated the effect of the photopolymer illumination condition on the quality of the displayed intensity image. As a projector, we achieved 82% phase to intensity conversion efficiency, which implies that the proposed method can potentially have much higher light efficiency than conventional projection display.”

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Publication: Journal of the Optical Society of Korea
Issue/Year: Journal of the Optical Society of Korea, Volume 12, Issue 4, December 2008, pp.319-325
DOI: 10.3807/JOSK.2008.12.4.319

Phase contrast microscopy with full numerical aperture illumination

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

Abstract:

“A modification of the phase contrast method in microscopy is presented, which reduces inherent artifacts and improves the spatial resolution. In standard Zernike phase contrast microscopy the illumination is achieved through an annular ring aperture, and the phase filtering operation is performed by a corresponding phase ring in the back focal plane of the objective. The Zernike method increases the spatial resolution as compared to plane wave illumination, but it also produces artifacts, such as the halo- and the shade-off effect. Our modification consists in replacing the illumination ring by a set of point apertures which are randomly distributed over the whole aperture of the condenser, and in replacing the Zernike phase ring by a matched set of point-like phase shifters in the back focal plane of the objective. Experimentally this is done by illuminating the sample with light diffracted from a phase hologram displayed at a spatial light modulator (SLM). The subsequent filtering operation is then done with a second matched phase hologram displayed at another SLM in a Fourier plane of the imaging pathway. This method significantly reduces the haloand shade-off artifacts whilst providing the full spatial resolution of the microscope.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 24, pp. 19821-19829
DOI: 10.1364/OE.16.019821

Generation of laser-induced cavitation bubbles with a digital hologram

Author(s): P. A. Quinto-Su, V. Venugopalan, and C.-D. Ohl

Abstract:

“We demonstrate a method using a spatial light modulator (SLM) to generate arbitrary 2-D spatial configurations of laser induced cavitation bubbles. The SLM acts as a phase hologram that controls the light distribution in the focal plane of a microscope objective. We generate cavitation bubbles over an area of 380×380 µm² with a 20x microscope objective through absorption of the pulsed laser light in a liquid ink solution. We demonstrate the ability to accurately position up to 34 micrometer sized bubbles using laser energies of 56 µJ.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 23, pp. 18964-18969
DOI: 10.1364/OE.16.018964

Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics

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

Abstract:

“In this paper we provide evidence of the temporal fluctuations of the phase modulation property of a liquid crystal on silicon (LCoS) display, and we analyze its effect when the device is used for displaying a diffractive optical element. We use a commercial twisted nematic LCoS display configured to produce a phase-only modulation, and we provide time resolved measurements of the diffraction efficiency that show rapid fluctuations of the phase modulation, in the millisecond order. We analyze how these fluctuations have to be considered in two typical methods for the characterization of the phase modulation: two beam interference and diffraction from a binary grating. We finally provide experimental results on the use of this device for displaying a computer generated hologram. A reduction of the modulation diffraction efficiency results from the phase modulation fluctuation.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 21, pp. 16711-16722 (2008)
DOI: 10.1364/OE.16.016711

A spatial light phase modulator with an effective resolution of 4 mega-pixels

Author(s): Daryl Preece; Eric Yao; Graham Gibson; Richard Bowman; Jonathan Leach; Miles Padgett

Abstract:

“We report the design, construction and characterization of a 4 mega-pixel, optically-addressed, spatial light modulator (OSLM). The intensity distribution corresponding to a kinoform is displayed across two wide-screen liquid crystal on silicon displays, the images of which are combined and relayed to the address face of a 40 mm aperture OSLM. This spatially varying intensity profile is converted into a phase hologram on the readout side of the OSLM. When illuminated at 532 nm we measure a first-order diffraction efficiency of ≈50% at 400 line pairs and ≈20% at 900 line pairs. We show that aberration associated with the non-flatness of the device can be corrected within software by modification of the hologram.”

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Publication: Journal of Modern Optics
Issue/Year: Journal of Modern Optics, Volume 55, Issue 18 October 2008 , pages 2945 – 2951
DOI: 10.1080/09500340802272357

Three-dimensional parallel holographic micropatterning using a spatial light modulator

Author(s): Nathan J. Jenness, Kurt D. Wulff, Matthew S. Johannes, Miles J. Padgett, Daniel G. Cole, and Robert L. Clark

Abstract:

“We present a micropatterning method for the automatic transfer and arbitrary positioning of computer-generated three-dimensional structures within a substrate. The Gerchberg-Saxton algorithm and an electrically addressed spatial light modulator (SLM) are used to create and display phase holograms, respectively. A holographic approach to light manipulation enables arbitrary and efficient parallel photo-patterning. Multiple pyramidal microstructures were created simultaneously in a photosensitive adhesive. A scanning electron microscope was used to confirm successful replication of the desired microscale structures. ”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 20, pp. 15942-15948 (2008)
DOI: 10.1364/OE.16.015942

Collisions of Dark Solitons in Elongated Bose-Einstein Condensates

Author(s): S. Stellmer, C. Becker, P. Soltan-Panahi, E.-M. Richter, S. Dörscher, M. Baumert, J. Kronjäger, K. Bongs, and K. Sengstock

Abstract:

“We present experimental data showing the head-on collision of dark solitons generated in an elongated Bose-Einstein condensate. No discernable interaction can be recorded, in full agreement with the fundamental theoretical concepts of solitons as mutually transparent quasiparticles. Our soliton generation technique allows for the creation of solitons with different depths; hence, they can be distinguished and their trajectories be followed. Simulations of the 1D-Gross-Pitaevskii equation have been performed to compare the experiment with a mean-field description.”

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Publication: Physical Review Letters
Issue/Year: Phys. Rev. Lett. 101, Issue 12, 120406 (2008)
DOI: 10.1103/PhysRevLett.101.120406
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