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Plasmonic optical tweezers: A long arm and a tight grip

 

nature

By taking advantage of the thermal gradient that is generated in plasmonic systems and by using an a.c. field, plasmonic tweezers can have a large radius of action and can trap and manipulate single nano-objects.

 

To have access to this paper, please visit:

http://www.nature.com/nnano/journal/v11/n1/full/nnano.2015.253.html

Plasmons Enhance Detection of Wavefront Aberrations

DUBLIN, Dec. 8, 2015 — A sensor that exploits plasmonics to gauge nanoscale distortions in lightwaves could yield more powerful tools for metrology and chemical sensing, as well as sharper microscopes.

The method detects wavefront aberrations indirectly by measuring changes in the reflectivity of gold films. It may be the first to use plasmons to address a classical optics problem, according to its developers at University College Dublin.

As light travels through water, the atmosphere and even human tissue its wavefront becomes distorted, blurring images and reducing resolution. It’s possible to correct for these distortions with adaptive optics by precisely measuring the shape of the wavefront.

Such measurements — albeit on relatively large scales — are used in astronomy to correct for atmospheric distortion.

Conventional wavefront sensors work by either mechanically sampling wavefronts with microlenses or other devices or measuring interference patterns. The latter approach requires the extra step of ensuring that the interacting light waves are in phase — meaning their waveforms overlap precisely.

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Cartesian wavefront derivatives can be determined by monitoring intensity variations across the reflected beam of light used to excite surface plasmon polaritons in the Kretschmann configuration. Courtesy of Optica/The Optical Society.


Now, by observing how efficiently incoming light creates surface plasmon polaritons (SPPs) on gold film, it’s possible to derive previously undetectable nanoscale distortions in the wavefronts.

SPPs arise when light meets an electrically conducting material, causing electrons to oscillate in a wavelike pulse that travels across the material’s surface. Any changes in the angle of incidence — as would occur from a distortion in the wavefront — affects the way the SPPs are formed. This directly affects how much light is reflected back from the surface.

“Since these polaritons are perfectly coupled to the light that forms them, any changes in their behavior would indicate a change in the waveform of light,” said Brian Vohnsen, a senior lecturer at University College Dublin. “We make use of the attenuation of the signal from the gold surface to simply convert the wavefront shape — or slope — into an intensity difference in a beam of light.”

This change is captured with cameras that are sensitive to minute changes in intensity.

To fully reconstruct the wavefront, the system requires two separate measurements made at 90° to one another. It is then possible to calculate the tiny changes in the actual wavefront based on the orthogonal intensity data points. The speed of the measurement is limited only by the speed of the cameras.

This type of sensor may find applications in the quality inspection of planar materials, films and coatings, the researchers said. It could also replace some wavefront sensors used in astronomy, microscopy and vision science.

The researchers are working to overcome two limitations in the current setup. The first is the requirement for simultaneous measurement of wavefront changes with two cameras. The second is improving the method by which the SPPs are “excited” on the surface of the gold film.

The results were published in Optica (doi: 10.1364/optica.2.001024 [open access]).

 

Reference: http://www.photonics.com/Article.aspx?PID=6&VID=124&IID=855&AID=58043

SPIE Optics + Photonics

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SPIE Optics + Photonics 2016, the largest international, multidisciplinary optical sciences and technology meeting in North America. The meeting where the latest research in optical engineering and applications, sustainable energy, nanotechnology, and organic photonics is presented.

 

For more information, please visit the following website:

http://spie.org/conferences-and-exhibitions/optics-and-photonics

CLEO: 2016

cleo

The leading peer-reviewed meeting on lasers & electro-optics.

CLEO (Conference on Lasers and Electro-Optics) serves as the premier international forum for scientific and technical optics, uniting the fields of lasers and opto-electronics by bringing together all aspects of laser technology, from basic research to industry applications.

Attendees have the opportunity to hear and present groundbreaking research, share ideas, and network with colleagues and luminaries. CLEO presents a world-renowned peer-reviewed program and offers high quality content from five core event elements:

ICNP 2016 The 9th International Conference on Nanophotonics

The International Conference on Nanophotonics (ICNP) will be held from 21-25 March 2016 at Academia Sinica, Taipei, Taiwan.

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This conference is a unique event where the latest advances in optics and photonics both in nano- and micro-scale will be reported and discussed. This conference primarily aims to explore novel ideas in nanophotonic science and technology that might enable technological breakthroughs in high impact areas such as biomedical and life sciences; information processing; communications; energy harvesting and storage; environment and conservation. The comprehensive coverage of conference themes, including microscopy and nanoscopy, silicon photonics; quantum optics; metamaterials; plasmonics; transformation optics; materials for micro- and nano-photonics; nanofabrication; and photonic devices, ensures researchers in this exciting field always have the opportunity to report their work and exchange information with fellow co-workers.

ICONN 2016 – International Conference on Nanoscience and Nanotechnology 7-11 Feb 2016

ICONN

National Convention Centre, Canberra, Australia

The aim of the 2016 International Conference On Nanoscience and Nanotechnology (ICONN 2016) is to bring together Australian and International communities (students, scientists, engineers and stake holders from academia, government laboratories, industry and other organisations) working in the field of nanoscale science and technology to discuss new and exciting advances in the field. ICONN will cover nanostructure growth, synthesis, fabrication, characterization, device design, theory, modeling, testing, applications, commercialisation, and health and safety aspects of nanotechnology.

The conference will feature plenary talks followed by technical symposia (parallel sessions) consisting of invited talks, oral and poster presentations.

Infrared spectroscopy with visible light

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Experimental set-up. A continuous-wave laser at 532 nm pumps two nonlinear crystals, where SPDC occurs. The crystals are placed in a vacuum chamber and CO2 is injected into the chamber. The interference pattern of the SPDC from the two crystals is imaged by a lens onto a slit of a spectrograph and recorded by a charge-coupled device (CCD) camera.

Spectral measurements in the infrared optical range provide unique fingerprints of materials, which are useful for material analysis, environmental sensing and health diagnostics1. Current infrared spectroscopy techniques require the use of optical equipment suited for operation in the infrared range, components of which face challenges of inferior performance and high cost. Here, Kalashnikov et al. develop a technique that allows spectral measurements in the infrared range using visible-spectral-range components. The technique is based on nonlinear interference of infrared and visible photons, produced via spontaneous parametric down conversion. The intensity interference pattern for a visible photon depends on the phase of an infrared photon travelling through a medium. This allows the absorption coefficient and refractive index of the medium in the infrared range to be determined from the measurements of visible photons. The technique can substitute and/or complement conventional infrared spectroscopy and refractometry techniques, as it uses well-developed components for the visible range

Reference:

Nature Photonics 10, 98–101 (2016) doi:10.1038/nphoton.2015.252
http://www.nature.com/nphoton/journal/v10/n2/full/nphoton.2015.252.html