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Stories and comments across the archive that link to osa.org.

Comments · 6

  1. direct link by Trepidity · · Score: 5, Informative · on Fireflies Bring Us Brighter LEDs

    The linked article is just a paraphrase of this press release, which has more details.

  2. Re:To Elaborate on the Submission by StressedEd · · Score: 1 · on Numerically Approximating the Wave Equation?
    I understand your frustration at there not being a "standard" package to solve EM (or scalar wave) problems -- I have ranted about this quietly on my own for a while. One would think that with the equations of Maxwell nearly 150 years old there should be some pretty standard solver techniques out there that would have been packaged up by now covering practically everything. The problem is - while it's easy to write down the equations and (naieve) methods of solving them the nitty-gritty of it all is both important and far more tricky than meets the eye! Each problem domain has its own issues and idiosyncrasy's. Likewise if you are interested in some quantaties more than others (e.g. far field / near field) that can drastically change your approach. Ultimately to have any chance of success you must approximate and the art of the approximation you choose is what matters. As the saying goes "If you want to go there, I wouldn't start from here".

    If you are trying to carry out some sort of electrically large scattering problem through inhomogeneous anisotropic materials - you are in for a tough ride. Unless you can approximate things away furiously you will soon find the problem computationally intractable.

    It sounds to me as though you really need to get a feel for the basics before embarking on anything too heavy. Time spent in reconnaissance is rarely wasted. Once you have an intuitive idea of how things work you will probably better understand the problem - hence be able to pick an appropriate solver.

    A good general starting point in my opinion (particularly in the scalar case) is the use of pseudospectral methods. These will allow you to describe the field propagating through materials in a reasonably tractable manner - they are not too much effort to understand, reasonably quick thanks to the magic of FFTW and surprisingly robust.

    I suspect your problem breaks down into three distinct domains:

    1. Getting the excitation field to the interaction region
    2. Modelling the (potentially complicated) interaction of the field with the surface
    3. Getting the field back from the interaction region to the detector.

    Since the excitation is presumably beam-like, a pseudospectral technique (particularly one with coordinate scaling) will probably help with 1) and 3). With finite difference techniques you must model the field step-by-step through space. With FFT methods you can jump from one plane to the other - this can be orders of magnitude faster than finite difference.

    How you manage 2 is the tricky part! The detail of this will depend strongly on what the material interaction is (e.g. will a scalar approximation suffice). I highly recommend you read Weng Cho Chew, Waves and Fields in Inhomogeneous Media for some pointers. Other things to look into:

    1. Green's function techniques (see, e.g. Martin et. al. for an accessible start point).
    2. Transfer matrix methods (see, e.g. Barns and Pendry)
    3. Discrete dipole scattering (see, e.g. Bruce Draine's DDSCAT)
    4. Multiple multipole methods (see, e.g. C. Hafner
    5. Finite Difference Time Domain (e.g. see the excellent MEEP from MIT) (see my warning below)
    6. Basis expansions and stratified media (similar to transfer matrix) see. Chew for details)

    A

  3. Re:Death by light by kebes · · Score: 4, Informative · on New Microscope Watches Cells in 3D
    Some more details about the technique. The writeup on the MIT site has more information. The technique is using laser interferometry:

    Feld and his colleagues have been able to image live, untreated cells by using an optical technique based on interferometry: a laser beam passed through a sample is compared with a reference beam of similar wavelength that is not passed through the cell. For example, it takes longer for light to travel through a cell than through, say, water. Researchers can measure that time delay, or phase shift, and then can map the cell and its motions on the scale of nanometers.
    This appears to be one of the earlier publications on the technique:
    "Cellular Organization and Substructure Measured Using Angle-Resolved Low-Coherence Interferometry", Wax A, Yang C, Backman V, Badizadegan K, Boone C, Dasari RR, Feld MS. Biophysical Journal 82: 2256-2264 (2002).

    In the experimental section of that article they say:

    Broadband light from a superluminescent diode (superluminescent diode (SLD) (EG&G, Gaithersburg, MD), output power 3 mW, center wavelength 845 nm, full width half-maximal bandwidth 22 nm...
    This appears to be one of their more recent publications:
    "Quantitative phase imaging of live cells using fast Fourier phase microscopy", Niyom Lue, Wonshik Choi, Gabriel Popescu, Takahiro Ikeda, Ramachandra R. Dasari, Kamran Badizadegan, and Michael S. Feld. Applied Optics, Vol. 46, Issue 10, pp. 1836-1842.

    In that paper they say:

    The second harmonic of the cw Nd:YAG laser (CrytaLaser, special custom-built module; wavelength 532nm, 500 mW) is used as an illumination source for a typical inverted microscope (Axiovert 100, Carl Zeiss).
    The illumination sources are not very intense, but are powerful enough to cause cell damage if they were highly focused. From looking over the papers it doesn't seem that this is the case. For what it's worth, the papers do not mention cell damage as being a concern.

    Overall the technique seems to have serious promise. It essentially involves doing laser interferometry on the sample at multiple angles, and reconstructing the 3D image. As they mention in their papers, it has the advantage of interfacing with conventional confocal microscope designs. Thus it could be added as an option on existing setups. It appears to have some exacting requirements (like all holography/interferometry it will be sensitive to vibrations, etc.), but overall seems like the type of thing that could be rapidly built into existing labs and commercial instruments.
  4. Re:Is this the actual research paper? by ultracool · · Score: 3, Informative · on Material With Negative Refractive Index Created
    Papers are typically submitted to arxiv.org at the time of submission to a journal. If accepted, it usually appears in the particular journal several months later. The paper was published in Optics Letters just this week, though it was posted on arxiv.org in August:

    http://ol.osa.org/abstract.cfm?id=119886 You have to keep in mind that before Arxiv.org papers (or any other pre-print archives) appear in a journal, you can't guaranteed that they have passed the peer-review process.

  5. Sandia Labs on course for more efficient lightbulb by Entropy+Unleashed · · Score: 0 · on The End of the Oil Age

    Science News Online has an article on a some grounbreaking research done at Sandia National Labs that has a very real possibility of leading to much more efficient solar cells and lightbulbs. The researchers have created a crystalline microstructure in tungsten that has much higher emissions at certain frequencies in the infrared when heated than Planck's Law can account for. A number of explanations have been proposed for this, but insufficient data exists as to which is correct. The phenomenon has been confirmed numerous times in over 100 different "photonic crystals", although no independent confirmation is mentioned. The researchers are currently attempting to locate another material with the necessary characteristics to duplicate the effect with visible light. If they are successful, we may soon see much more efficient lightbulbs and solar cells in our homes, obviating the need for hydrocarbon fuels.

    The abstract is available here, while the article can be read here.

  6. Resonance is Faster than Producing Bubbles Using I by voidzero · · Score: 1 · on Pure Optical Network Switches
    Nanovation Technologies prototyped an optical switch on 15 April 1999. Further info here.

    At OFC2000 today, Nanovation displayed new optical switches, splitters and modulators.
    From their press release:
    "These switches, splitters and modulators are the first of what will be an extensive offering of integrated photonic components from Nanovation. These products will help businesses and consumers access the full power of all-optical communications in a cost-effective manner," said G. Robert Tatum, president and CEO of Nanovation. "Companies will now be able to build their own customized, optical integrated circuits, thanks to the advanced capabilities of Nanovation components."

    Nanovation's new and revolutionary Nanoshutterä technology outperforms other optical switching products by providing a latching switch mechanism for reduced power, very wideband operation, and the ability to integrate these switches with other functional components. This innovative patent-pending technology combines silicon MEMS switches with a proprietary silica-on-silicon wave-guide process, which will enable Nanovation to offer optical components not only with substantial size and cost advantages, but unparalleled flexibility in optical systems architecture - all on a single integrated device.

    The offerings from the switch family using Nanoshutterä technology include versions of the following:
    Wide band 1X2 optical switch
    Wide band 1X2 optical switch with integrated 5% monitoring taps
    Wide band 2X2 optical switch
    Wide band 2X2 optical switch with integrated 5% monitoring taps
    Wide band 1X4 optical switch
    Wide band 1X8 optical switch
    Wide band 1X16 optical switch

    Nanovation's new offerings for the 1310 nm and 1550 nm telecommunications bands include versions of the following members of the silica-on-silicon wave-guide splitters product family using NanoblockTM technology.
    Single mode 1X8 wide band optical splitter
    Single mode 1X16 wide band optical splitter
    Single mode 2X8 wide band optical splitter
    Single mode 2X16 wide band optical splitter

    The company also demonstrated its 1550 nm high-speed switching technology using Indium Phosphide materials. First components planned around this technology include sub-nanosecond optical switches and high-speed modulators.

    A listing of their product line is here. You can download the specs there in PostScript format.

    I have been following this company with some interest since their mention on /. Q1 1999.