| 1. |
- Zhang, Miao, et al.
(författare)
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Optical detection of two-color-fluorophore barcode for nanopore DNA sensing
- 2015
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Konferensbidrag (refereegranskat)abstract
- A simple schematic on parallel optical detection of two-fluorophore barcode for single-molecule nanopore sensing is presented. The chosen two fluorophores, ATTO-532 and DY-521-XL, emitting in well-separated spectrum range can be excited at the same wavelength. A beam splitter was employed to separate signals from the two fluorophores and guide them to the same CCD camera. Based on a conventional microscope, sources of background in the nanopore sensing system, including membranes, compounds in buffer solution, and a detection cell was characterized. By photoluminescence excitation measurements, it turned out that silicon membrane has a negligible photoluminescence under the examined excitation from 440 nm to 560 nm, in comparison with a silicon nitrite membrane. Further, background signals from the detection cell were suppressed. Brownian motion of 450 bps DNA labelled with single ATTO-532 or DY-521-XL was successfully recorded by our optical system.
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| 2. |
- Bratkovsky, A. M., et al.
(författare)
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Properties of nanostructured metamaterials at optical frequencies
- 2008
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Konferensbidrag (refereegranskat)abstract
- A variety of metamaterials has been demonstrated recently that support backward waves and negative refraction (Negative Index Materials, NIM.) In particular, these materials enable sub-wavelength resolution that makes them even more interesting, especially in optical domain rather than at microwave frequencies where their unusual properties were known for decades. We describe below theoretical and experimental studies of the so-called 'fishnet' metal-spacer holearray metamaterials, which exhibit NIM behavior at optical frequencies, having unit cell size of a few 100s nm. We demonstrate experimentally that their refractive index can be modulated very fast and very strongly (from -2.4 to -1.5) around the communication wavelength of =1.55 um, in good agreement with the FDTD results. We also discuss a problem of loss compensation in those materials with hefty Ohmic losses by using gain media and local field enhancement in metallic nanoparticles ensembles that enable SERS.
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| 3. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Contrast-enhanced dual-energy subtraction imaging using electronic spectrum-splitting and multi-prism x-ray lenses
- 2008
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Ingår i: Medical Imaging 2008 - Physics of Medical Imaging. - San Diego, CA, USA : SPIE. - 9780819470973 ; , s. 91310-91310
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Konferensbidrag (refereegranskat)abstract
- Dual-energy subtraction imaging (DES) is a method to improve the detectability of contrast agents over a lumpy background. Two images, acquired at x-ray energies above and below an absorption edge of the agent material, are logarithmically subtracted, resulting in suppression of the signal from the tissue background and a relative enhancement of the signal from the agent. Although promising, DES is still not widely used in clinical practice. One reason may be the need for two distinctly separated x-ray spectra that are still close to the absorption edge, realized through dual exposures which may introduce motion unsharpness. In this study, electronic spectrum-splitting with a silicon-strip detector is theoretically and experimentally investigated for a mammography model with iodinated contrast agent. Comparisons are made to absorption imaging and a near-ideal detector using a signal-to-noise ratio that includes both statistical and structural noise. Similar to previous studies, heavy absorption filtration was needed to narrow the spectra at the expense of a large reduction in x-ray flux. Therefore, potential improvements using a chromatic multi-prism x-ray lens (MPL) for filtering were evaluated theoretically. The MPL offers a narrow tunable spectrum, and we show that the image quality can be improved compared to conventional filtering methods.
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| 4. |
- Kamp, M., et al.
(författare)
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Technology and properties of photonic crystal based active and passive optoelectronic devices
- 2004
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Konferensbidrag (refereegranskat)abstract
- We have investigated tunable photonic crystal waveguide lasers and their integration with a photonic crystal based combiner. The devices were fabricated on a layer structure with active and passive sections. The lasers are formed in the active part and consist of two longitudinally coupled photonic crystal waveguide segements. Photonic crystals based waveguides and a combiner, both defined in the passive sections, are used to direct the light of the two sources into a single output waveguide. Tuning over a 30 nm range is demonstrated. The two sources can be operated independently, allowing the simultaneous transmission of two freely selectable wavelengths.
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| 5. |
- Lysak, V. V., et al.
(författare)
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The influence of gain nonlevearities on distortion in semiconductor lasers
- 2004
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Konferensbidrag (refereegranskat)abstract
- The modulation response and second harmonic distortion was analyzed for different gain models and compared with exact integral gain models. It was shown that if we modulate the laser around steady state with a signal, it would induce carrier and photon fluctuations. The second order distortion depended on the carrier and photon modulation response, the internal mixing process determined by the Hessian matrix creating a fictive injection signal and the carrier and photon modulation response at intermodulation frequency. It was found that the approximate model has a reasonable good agreement with an exact comprehensive gain model at all frequencies and pumping currents.
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| 6. |
- Qiu, Min, et al.
(författare)
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Transformation optics and invisibility cloaks
- 2008
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Konferensbidrag (refereegranskat)abstract
- In this paper, we briefly summarize the theory of transformation optics and introduce its application in achieving perfect invisibility cloaking. In particular, we theoretically show how the task of realizing cylindrical invisibility cloaks can be eased by using either structural approximation or material simplification. The corresponding invisibility performances of the approximate or simplified cylindrical cloaks are presented in detail.
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