P. Miao, Z. Zhang, J. Sun, W. Walasik, N.M. Litchinitser, and L. Feng

ORBITAL ANGULAR MOMENTUM MICROLASER  (2016)

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Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission.

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Dunzhao Wei, Yongmei Wang, Dongmei Liu, Yunzhi Zhu, Weihao Zhong, Xinyuan Fang, Yong Zhang, Min Xiao

NONDESTRUCTIVE ON-CHIP DETECTION OF OPTICAL ORBITAL ANGULAR MOMENTUM THROUGH A SINGLE PLASMONIC NANOHOLE (2016) (pdf)

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Optical orbital angular momentum (OAM) provides an additional dimension for photons to carry information in high-capacity optical communication. Although the practical needs have intrigued the generations of miniaturized devices to manipulate the OAM modes in various integrated platforms, the on-chip OAM detection is still challenging to match the newly-developed compact OAM emitter and OAM transmission fiber. Here, we demonstrate an ultra-compact device, i.e., a single plasmonic nanohole, to efficiently measure an optical beam's OAM state in a nondestructive way. The device size is reduced down to a few hundreds of nanometers, which can be easily fabricated and installed in the current OAM devices. It is a flexible and robust way for in-situ OAM monitoring and detection in optical fiber networks and long-distance optical communication systems. With proper optimization of the nanohole parameters, this approach could be further extended to discriminate the OAM information multiplexed in multiple wavelengths and polarizations.

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LASER BEAMS WITH A 'TWIST' (2016) (pdf)

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Producing light with a controlled spin in a laser has been known for decades, but producing OAM beams inside a laser is not so simple. Light carrying OAM is created by twisting the phase of light into a helical shape, forming a spiral. Because the twisting of the pattern gets tighter and tighter as you move towards the centre of the beam, the light disappears and such beams are often called doughnut beams or vortex beams.

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The novelty was to realise that by using custom-geometric phase optics to map polarisation to OAM, the laser could be designed to tell the difference between the clockwise and anticlockwise light. The control is achieved by simply rotating a single optical element inside the laser, without any need for realignment.

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Importantly, the same laser can produce any combination of these OAM beams and various polarisations of light. The team was able to show that the outcome was the generation of arbitrary vector vortex beams, known as higher-order Poincaré sphere beams.

 

 

Производить свет с контролируемой спина в лазере была известна на протяжении десятилетий, но производить балки ОАМ внутри лазера не так просто. Свет несущий ОАМ создается путем скручивания фазы света в спиральную форму, образуя спираль. Потому что перекручивание узор туже и туже, как вы двигаться по направлению к центру пучка, свет исчезает, и такие пучки часто называют балки пончик или вихревых Пучков.

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Новинка должна была понимать, что, используя пользовательские геометрические фазы оптики на карте поляризации в ОАМ, лазер может быть создан, чтобы рассказать разницу между по часовой стрелке и против часовой стрелки света. Управление осуществляется простым поворотом одного оптического элемента внутри лазера, без необходимости перестройки.

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Главное, тот же лазер может производить любые комбинации этих ОАМ балки и различные поляризации света. Команда смогла показать, что результат генерации произвольных векторных вихревых Пучков, известный как высокого Пучков сфере Пуанкаре.

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Christina J. Naify, Charles A. Rohde, Theodore P. Martin, Michael Nicholas, Matthew D. Guild, Gregory J. Orris

GENERATION OF TOPOLOGICALLY DIVERSE ACOUSTIC VORTEX BEAMS USING A COMPACT METAMATERIAL APERTURE (2016) (pdf)

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Here, we present a class of metamaterial-based acoustic vortex generators which are both geometrically simple and broadly tunable. The aperture overcomes the significant limitations of both active phasing systems and existing passive coded apertures. The metamaterial approach generates topologically diverse acoustic vortex waves motivated by recent advances in leaky wave antennas by wrapping the antenna back upon itself to produce an acoustic vortex wave antenna. We demonstrate both experimentally and analytically that this single analog structure is capable of creating multiple orthogonal orbital angular momentum modes using only a single transducer. The metamaterial design makes the aperture compact, with a diameter nearly equal to the excitation wavelength and can thus be easily integrated into high-density systems. Applications range from acoustic communications for high bit-rate multiplexing to biomedical devices such as microfluidic mixers.

 

 

Xiaomei Zhang, Baifei Shen, Yin Shi, Lingang Zhang, Liangliang Ji, Xiaofeng Wang, Zhizhan Xu, Toshiki Tajima

INTENSE HARMONICS GENERATION WITH CUSTOMIZED PHOTON FREQUENCY AND OPTACAL VORTEX (2016) (pdf)

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An optical vortex with orbital angular momentum (OAM) enriches the light and matter interaction process, and helps reveal unexpected information in relativistic nonlinear optics. A scheme is proposed for the first time to explore the origin of photons in the generated harmonics, and produce relativistic intense harmonics with expected frequency and an optical vortex. When two counterpropagating Laguerre–Gaussian laser pulses impinge on a solid thin foil and interact with each other, the contribution of each input pulse in producing harmonics can be distinguished with the help of angular momentum conservation of photons, which is almost impossible for harmonic generation without an optical vortex. The generation of tunable, intense vortex harmonics with different photon topological charge is predicted based on the theoretical analysis and three-dimensional particle-in-cell simulations. Inheriting the properties of OAM and harmonics, the obtained intense vortex beam can be applied in a wide range of fields, including atom or molecule control and manipulation.

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R. Géneaux, A. Camper, T. Auguste, O. Gobert, J. Caillat, R. Taïeb & T. Ruchon

SYNTHESIS AND CHARACTERIZATION OF ATTOSECOND LIGHT VORTICES IN THE EXTREME ULTRAVIOLET (2016) (pdf)

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Infrared and visible light beams carrying orbital angular momentum (OAM) are currently thoroughly studied for their extremely broad applicative prospects, among which are quantum information, micromachining and diagnostic tools. Here we extend these prospects, presenting a comprehensive study for the synthesis and full characterization of optical vortices carrying OAM in the extreme ultraviolet (XUV) domain. We confirm the upconversion rules of a femtosecond nfrared helically phased beam into its high-order harmonics, showing that each harmonic order carries the total number of OAM units absorbed in the process up to very high orders (57). This allows us to synthesize and characterize helically shaped XUV trains of attosecond pulses. To demonstrate a typical use of these new XUV light beams, we show our ability to generate and control, through photoionization, attosecond electron beams carrying OAM. These breakthroughs pave the route for the study of a series of fundamental phenomena and the development of new ultrafast diagnosis tools using either photonic or electronic vortices.

 

 

J. Luo, M. Chen, M. Zeng, J. Vieira, L.L. Yu, S.M. Weng, L.O. Silva, D.A. Jaroszynski, Z.M. Sheng, J. Zhang

A COMPACT TUNABLE POLARIZED X - RAY SOURCE BASED ON LASER - PLASMA HELICAL UNDULATORS (2016) (pdf)

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Laser wakefield accelerators have great potential as the basis for next generation compact radiation sources because of their extremely high accelerating gradients. However, X-ray radiation from such devices still lacks tunability, especially of the intensity and polarization distributions. Here we propose a tunable polarized radiation source based on a helical plasma undulator in a plasma channel guided wakefield accelerator. When a laser pulse is initially incident with a skew angle relative to the channel axis, the laser and accelerated electrons experience collective spiral motions, which leads to elliptically polarized synchrotron-like radiation with flexible tunability on radiation intensity, spectra and polarization. We demonstrate that a radiation source with millimeter size and peak brilliance of 2×1019 photons/s/mm2/mrad2/0.1% bandwidth can be made with moderate laser and electron beam parameters. This brilliance is comparable with third generation synchrotron radiation facilities running at similar photon energies, suggesting that laser plasma based radiation sources are promising for advanced applications.

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Alberto A. Lutman, James P. MacArthur, Markus Ilchen, Anton O. Lindahl, Jens Buck, Ryan N. Coffee, Georgi L. Dakovski, Lars Dammann, Yuantao Ding, Hermann A. Dürr, Leif Glaser, Jan Grünert, Gregor Hartmann, Nick Hartmann, Daniel Higley,         Konstantin Hirsch, Yurii I. Levashov, Agostino Marinelli, Tim Maxwell, Ankush Mitra, Stefan Moeller, Timur Osipov, Franz Peters, Marc Planas, Ivan Shevchuk et al.

POLARIZATION CONTROL IN AN X - RAY FREE - ELECTRON LASER (2016) (pdf)

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X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98–0.04+0.02 at 707eV and may be scanned in energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. Energy differences of ΔE/E=2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.

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Junxiao Zhou, Wenshuai Zhang, Yachao Liu, Yougang Ke, Yuanyuan Liu, Hailu Luo, Shuangchun Wen

SPIN-DEPENDENT MANIPULATING OF VECTOR BEAMS BY TAILORING POLARIZATION (2016) (pdf)

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We examine the spin-dependent manipulating of vector beams by tailoring the inhomogeneous polarization. The spin-dependent manipulating is attributed to the spin-dependent phase gradient in vector beams, which can be regarded as the intrinsic feature of inhomogeneous polarization. The desired polarization can be obtained by establishing the relationship between the local orientation of polarization and the local orientation of the optical axis of waveplate. We demonstrate that the spin-dependent manipulating with arbitrary intensity patterns can be achieved by tailoring the inhomogeneous polarization. It should be note that the varying polarization with a full period can be regard as spanning the equator of the Poincaré sphere.

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Weixing Shu, Yachao Liu, Yougang Ke, Xiaohui Ling, Zhenxing Liu, Bin Huang, Hailu Luo, and Xiaobo Yin

PROPAGATION MODEL FOR VECTOR BEAMS GENERATED BY METASURFACES (2016) (pdf)

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A propagation model of vector beams generated by metasurfaces based on vector diffraction theory is established theoretically and verified experimentally. Considering the Pancharatnam-Berry phase introduced by the metasurface, analytical forms of vector beams for arbitrary incident polarization and topological charge of metasurfaces are found in the Fresnel and Fraunhofer diffraction regions, respectively. The complex amplitude of the resultant vector beam can be described in terms of a confluent hypergeometric function, with an intensity profile that manifests concentric rings in the Fresnel region and a single ring in the Fraunhofer one. Fraunhofer diffraction provides a method to create vector beams with simultaneously high purity and modal power. Further experiments verify the theoretical results.

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Yi Zhang, Peng Li, Sheng Liu, Lei Han, Huachao Cheng, and Jianlin Zhao

MANIPULATING SPIN - DEPENDENT SPLITTING OF VECTOR ABRUPTLY AUTOFOCUSING BEAM BY ENCODING COSINE - AZIMUTHAL VARIANT PHASES (2016) (pdf)

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We report the realization of spin-dependent splitting of vector abruptly autofocusing beam (AAB) by encoding cosine-azimuthal variant phases. By employing the local spatial frequency (LSF), we reveal an approximation mapping relationship between focal field intensity of the two spin components and the pertinent phase distribution of input field. As well as theoretical analysis, we present experimental demonstrations of this guidance. Special focal field intensity, polarization and phase are realized by consciously managing the cosine-azimuthal variant phase. This distinctive focal field of vector AAB may have a broad range of applications in harnessing the spin-orbit coupling, optical trapping and laser machining.

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Zi-Yu Chen & Alexander Pukhov

BRIGHT HIGH - ORDER HARMONIC GENERATION WITH CONTROLLABLE POLARIZATION FROM A RELATIVISTIC PLASMA MIRROR (2016) (pdf)

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Ultrafast extreme ultraviolet (XUV) sources with a controllable polarization state are powerful tools for investigating the structural and electronic as well as the magnetic properties of materials. However, such light sources are still limited to only a few free-electron laser facilities and, very recently, to high-order harmonic generation from noble gases. Here we propose and numerically demonstrate a laser–plasma scheme to generate bright XUV pulses with fully controlled polarization. In this scheme, an elliptically polarized laser pulse is obliquely incident on a plasma surface, and the reflected radiation contains pulse trains and isolated circularly or highly elliptically polarized attosecond XUV pulses. The harmonic polarization state is fully controlled by the laser–plasma parameters. The mechanism can be explained within the relativistically oscillating mirror model. This scheme opens a practical and promising route to generate bright attosecond XUV pulses with desirable ellipticities in a straightforward and efficient way for a number of applications.

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