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

Far field subwavelength focusing using optical eigenmodes

Author(s): Jörg Baumgartl, Sebastian Kosmeier, Michael Mazilu, Edward T. F. Rogers, Nikolay I. Zheludev, and Kishan Dholakia.

Abstract:

“We report the focusing of light to generate a subdiffractive, subwavelength focal spot of full width half maximum 222 nm at an operating wavelength of 633 nm using an optical eigenmode approach. Crucially, the spot is created in the focal plane of a microscope objective thus yielding a practical working distance for applications. The optical eigenmode approach is implemented using an optimal superposition of Bessel beams on a spatial light modulator. The effects of partial coherence are also discussed. This far field method is a key advance toward the generation of subdiffractive optical features for imaging and lithographic purposes.”

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Publication: Applied Physics Letters
Issue/Year: Appl. Phys. Lett. 98, 181109 (2011)
DOI: 10.1063/1.3587636

A high speed wavefront determination method based on spatial frequency modulations for focusing light through random scattering media

Author(s): Meng Cui

Abstract:

“A large number of degrees of freedom are required to produce a high quality focus through random scattering media. Previous demonstrations based on spatial phase modulations suffer from either a slow speed or a small number of degrees of freedom. In this work, a high speed wavefront determination technique based on spatial frequency domain wavefront modulations is proposed and experimentally demonstrated, which is capable of providing both a high operation speed and a large number of degrees of freedom. The technique was employed to focus light through a strongly scattering medium and the entire wavefront was determined in 400 milliseconds, ~three orders of magnitude faster than the previous report.”

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Publication:Optics Express
Issue/Year: Optics Express, Vol. 19, Issue 4, pp. 2989-2995 (2011)
DOI: 10.1364/OE.19.002989

Dynamic generation of Debye diffraction-limited multifocal arrays for direct laser printing nanofabrication

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

Abstract:

“We propose a Debye-theory-based iterative method to produce accurate phase patterns for generating highly uniform diffraction-limited multifocal arrays with a high-NA objective. It is shown that by using the Debye method, the uniformity of the diffraction-limited focal arrays can reach 99%, owing to the critical consideration of the depolarization effect associated with high-NA objectives. The generated phase patterns are implemented in fast dynamic laser printing nanofabrication for the generation of individually controlled high-quality microvoid arrays in a solid polymer material by a single exposure of a femtosecond laser beam. As a result of the high-quality multifocal arrays, functional three-dimensional photonic crystals possessing multiple stopgaps with suppression up to 80% in transmission spectra are demonstrated.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 36, Issue 3, pp. 406-408 (2011)
DOI: 10.1364/OL.36.000406

Frequency bandwidth of light focused through turbid media

Author(s): Frerik van Beijnum, Elbert G. van Putten, Ad Lagendijk, and Allard P. Mosk

Abstract:

“We study the effect of frequency detuning on light focused through turbid media. By shaping the wavefront of the incident beam light is focused through an opaque scattering layer. When detuning the laser we observe a gradual decrease of the focus intensity, while the position, size,and shape of the focus remain the same within experimental accuracy. The frequency dependence of the focus intensity follows a measured speckle correlation function. We support our experimental findings with calculations based on transport theory. Our results imply wavefront shaping methods can be generalized to allow focusing of optical pulses in turbid media.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 36, Issue 3, pp. 373-375 (2011)
DOI: 10.1364/OL.36.000373

Constructing petal modes from the coherent superposition of Laguerre-Gaussian modes

Author(s): Darryl Naidoo, Andrew Forbes, Kamel Ait-Ameur, Marc Brunel

Abstract:

“An experimental approach in generating Petal-like transverse modes, which are similar to what is seen in porro-prism resonators, has been successfully demonstrated. We hypothesize that the petal-like structures are generated from a coherent superposition of Laguerre-Gaussian modes of zero radial order and opposite azimuthal order. To verify this hypothesis, visually based comparisons such as petal peak to peak diameter and the angle between adjacent petals are drawn between experimental data and simulated data. The beam quality factor of the Petal-like transverse modes and an inner product interaction is also experimentally compared to numerical results.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE 7913, 791304 (2011)
DOI: 10.1117/12.876854

Dynamic space shaping of intense ultrashort laser light with blazed-type gratings

Author(s): I. Marienko, V. Denisenko, V Slusar, and M. Soskin

Abstract:

“A beam shaper for dynamic transversal shaping of broadband laser pulses that utilizes a blazed ruled grating and a blazed-type grating simulated on Spatial Light Modulator was demonstrated. The introduced shaper scheme is an extension of 2f-2f scheme [Mariyenko, et al., Opt. Express 13, 7599 (2005)] where the two thin holograms with matched grating constants performed light shaping. The new scheme utilizes the diffraction gratings with different grating constants. Dispersion-free light shaping is achieved by means of the intermediate transversal light beam magnification. The magnification balances the mismatch in the grating constants resulting in total residual angular dispersion compensation. In turn, the magnified beam covers a greater area on the modulator matrix thus reducing the incident light power density by a value equal to square of the magnification factor. It translates to the safe-operation threshold extension of the modulator allowing shaping pulses that are powerful enough to be used in the applications. With a proper components selection, the throughput efficiency of the shaper can be well above 40%. A proper shaper operation was demonstrated with the 140-fs Ti:Sapphire oscillator. Theoretical calculations support the conclusions.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 18, Issue 24, pp. 25143-25150 (2010)
DOI: 10.1364/OE.18.025143

Increasing multimode fiber transmission capacity by mode selective spatial light phase modulation

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

Abstract:

“We propose spatial light modulation with binary phase filters to increase the transmission bandwidth of multimode fibers. In the experiment more than 300 % of bandwidth enhancement is obtained.”

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Publication: ECOC Proceedings
Issue/Year: 36th European Conference and Exhibition on Optical Communication (ECOC), 2010
DOI: 10.1109/ECOC.2010.5621465

Imaging through turbid layers by scanning the phase conjugated second harmonic radiation from a nanoparticle

Author(s): Chia-Lung Hsieh, Ye Pu, Rachel Grange, Grégoire Laporte, Demetri Psaltis

Abstract:

“We demonstrate imaging through a turbid layer by using digital phase conjugation of the second harmonic field radiated from a beacon nanoparticle. We show that the phase-conjugated focus can be displaced from its initial position by illuminating the same region of the turbid layer with an angular offset. An image is obtained by scanning the phase-conjugated focus through the turbid layer in a region around the nanoparticle. We obtain a clear image of the target by measuring the light transmitted through it when scanning the focused beam.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 18, Issue 20, pp. 20723-20731 (2010)
DOI: 10.1364/OE.18.020723

Application of cooled spatial light modulator for high power nanosecond laser micromachining

Author(s): Rainer J. Beck, Jonathan P. Parry, William N. MacPherson, Andrew Waddie, Nick J. Weston, Jonathan D. Shephard, and Duncan P. Hand

Abstract:

“The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 18, Issue 16, pp. 17059-17065 (2010)
DOI: 10.1364/OE.18.017059