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

Quantum control of electron spins in the two-dimensional electron gas of a CdTe quantum well with a pair of Raman-resonant phase-locked laser pulses

Author(s): Timothy M. Sweeney, Carey Phelps, and Hailin Wang

Abstract:

“We demonstrated optical spin control of a two-dimensional electron gas in a modulation-doped CdTe quantum well by driving a spin-flip Raman transition with a pair of phase-locked laser pulses. In contrast to single-pulse optical spin control, which features a fixed spin-rotation axis, manipulation of the initial relative phase of the pulse pair enables us to control the axis of the optical spin rotation. We show that the Raman pulse pair acts like an effective microwave field, mapping the relative optical phase onto the phase of the electron spin polarization and making possible ultrafast, all-optical, and full quantum control of the electron spins.”

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Publication: Physical Review B, (subscription required)

Issue/Year/DOI: Phys. Rev. B, Volume 84, Issue 7, (2011)
doi:10.1103/PhysRevB.84.075321

Arbitrarily shaped high-coherence electron bunches from cold atoms

Author(s): A. J. McCulloch, D. V. Sheludko, S. D. Saliba, S. C. Bell, M. Junker, K. A. Nugent & R. E. Scholten

Abstract:

“Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.”

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Publication: Nature Physics, (subscription required)

Issue/Year/DOI: Nature Physics, 7, 785–788, (2011)
doi:10.1038/nphys2052

Generation of Optical Vortices by Linear Phase Ramps

Author(s): Sunil Vyas

Abstract:

“Generation of optical vortices using linear phase ramps is experimentally demonstrated. When two regions of a wavefront have opposite phase gradients then along the line of phase discontinuity vortices can be generated. It is shown that vortices can evolve during propagation even with the unequal magnitude of tilt in the two regions of the wavefront. The number of vortices and their location depend upon the magnitude of tilt. vortex generation is experimentally realized by encoding phase mask on spatial light modulator and their presence is detected interferometrically. Numerical simulation has been performed to calculate the diffracted intensity distribution from the phase mask, and presence of vortices in the diffracted field is detected by computational techniques.”

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Publication: International Journal of Optics, (free download)

Issue/Year/DOI: International Journal of Optics, Volume 2012, Article ID 794259, 6 pages, (2012)
doi:10.1155/2012/794259

Implementation of phase-shift patterns using a holographic projection system with phase-only diffractive optical elements

Author(s): Wei-Feng Hsu, Yu-Wen Chen, and Yuan-Hong Su

Abstract:

“We proposed a method to implement spatial phase-shift patterns with subdiffraction limited features through a holographic projection system. The input device of the system displayed phase-only diffractive optical elements that were calculated using the iterative Fourier-transform algorithm with the dummy-area method. By carefully designing the target patterns to the algorithm, the diffractive optical elements generated the Fourier-transformed images containing the phase-shift patterns in which the widths of dark lines were smaller than the diffraction limit. With these demonstrations, we have successfully shown that the near-field phase-shift lithographic technique can be realized through an inexpensive maskless lithographic system and can still achieve subdiffraction limited images.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 50, Issue 20, pp. 3646-3652 (2011)
doi:10.1364/AO.50.003646

Holographic display with tilted spatial light modulator

Author(s): Tomasz Kozacki

Abstract:

“In this paper, we analyze a holographic display system utilizing a phase-only spatial light modulator (SLM) based on liquid crystal on silicon (LCoS). An LCoS SLM works in reflection, and, in some applications, it is convenient to use with an inclined illumination. Even with a highly inclined illumination, the holographic display is capable of good-quality image generation. We show that the key to obtain high-quality reconstructions is the tilt-dependent calibration and algorithms. Typically, an LCoS SLM is illuminated with a plane wave with normal wave vector. We use inclined illumination, which requires development of new algorithms and display characterization. In this paper we introduce two algorithms. The first one is designed to process a digital hologram captured in CCD normal configuration, so it can be displayed in SLM tilted geometry, while the second one is capable of synthetic hologram generation for tilted SLM configuration. The inclined geometry asymmetrically changes the field of view of a holographic display. The presented theoretical analysis of the aliasing effect provides a formula for the field of view as a function of SLM tilt. The incidence angle affects SLM performance. Both elements of SLM calibration, i.e., pixel phase response and wavefront aberrations, strongly depend on SLM tilt angle. The effect is discussed in this paper. All of the discussions are accompanied with experimental results.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 50, Issue 20, pp. 3579-3588 (2011)
doi:10.1364/AO.50.003579

Binary-Phase Spatial Light Filters for Mode-Selective Excitation of Multimode Fibers

Author(s): Stepniak, G.; Maksymiuk, L.; Siuzdak, J.;

Abstract:

“In this paper, spatial light modulation is proposed to increase the transmission capacity of graded-index multimode fibers. In the method, selected linearly polarized eigenmodes of the fiber are excited using simple binary-phase spatial filters. Numerical results indicate that the selectivity of the method is very high, also for fibers with perturbed profiles. The excess attenuation of the method is very low. In the experiment, a threefold increase of fiber bandwidth for several filters is obtained.”

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Publication: Journal of Lightwave Technology, (subscription required)

Issue/Year/DOI: Journal of Lightwave Technology, Volume: 29 Issue: 13, P.1980 – 1987 (2011)
doi:10.1109/JLT.2011.2155621

Mean focal length of an aberrated lens

Author(s): Cosmas Mafusire and Andrew Forbes

Abstract:

“We outline an approach for the calculation of the mean focal length of an aberrated lens and provide closed-form solutions that show that the focal length of the lens is dependent on the presence of defocus, x-astigmatism, and spherical aberration. The results are applicable to Gaussian beams in the presence of arbitrary-sized apertures. The theoretical results are confirmed experimentally, showing excellent agreement. As the final results are in algebraic form, the theory may readily be applied in the laboratory if the aberration coefficients of the lens are known.”

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Publication: Journal of the Optical Society of America A, (subscription required)

Issue/Year/DOI: JOSA A, Vol. 28, Issue 7, pp. 1403-1409 (2011)
doi:10.1364/JOSAA.28.001403