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    • Volume 47, Issue 5

    More content from Volume 47, Issue 5

    Cut-away schematic of an organic photodetector fabricated on a silicon AFM tip shows the organic thin-film and electrode structure (a). Scanning of an aperture in a silver film back-illuminated at λ = 475 nm produces simultaneous topographic and optical (photocurrent) signals (b) and (c). The detector photocurrent measured during the scan of the dotted line in (c) is shown in (d).
    Advances in the fabrication of organic thin-film-based photodetectors and their combination with atomic force microscopy probes enable simultaneous high-resolution optical and...
    May 1, 2011
    Since beginning operations in 2002, the more than 800 scientists working on the Laser Interferometer Gravitational-Wave Observatory have been anxious to observe tiny variations...
    May 1, 2011
    (Courtesy of Michael Grogan)
    FIGURE 1. A scanning-electron micrograph shows the cleaved endface of a hollow-core PCF used to guide and compress 540 nm pulses (a). The core diameter is 5.6 μm. The irregularity of some holes in the cladding demonstrates the difficulty of fabricating this fiber due to runaway variations in hole size during the draw. The damage around the core was caused during the fiber cleave; although the fiber as a whole is robust, the individual struts are extremely thin. Despite this, the coupling efficiency into this fiber is still greater than 60%. (Courtesy of Brian Mangan). The output of a HC-PCF transmitting ultrashort green pulses is seen on a white piece of paper, revealing the fiber’s high-quality far-field mode profile (b).
    The capability of hollow-core photonic-crystal fiber to transmit ultrahigh-power femtosecond pulses without distortion has been extended from the infrared to the visible; compression...
    May 1, 2011
    (Courtesy of Mitsubishi Electric)
    FIGURE 1. Diamond Vision LED displays use two optical innovations to improve performance for ultralarge displays: “Quad Dot Pattern” technology (a) in which a color pixel is created from four dots—two red, one green, and one blue—in a configuration that allows a screen processor to share dots between adjacent pixels to create a “dynamic” pixel for increased viewing resolution; and individual shaders for each color LED (b) that give true colors when viewing at oblique angles, rather than multishading architectures that can obscure whole LED colors in a group, radically changing the color appearance.
    While many consumer display technologies for laptops, cell phones, and televisions have reached maturity, public displays and digital signage may have the largest growth potential...
    May 1, 2011
    FIGURE 1. A new wafer-scale etching technique can create refractive micro-optic elements in calcium fluoride.
    Using non-traditional etching techniques, it is possible to fabricate diffractive/refractive calcium-fluoride (CaF2) micro-optics for deep-UV excimer laser systems that can increase...
    May 1, 2011
    FIGURE 1. To prevent destructive interference of the generated radiation in the far field, every other gap between the interdigitated metallic stripes of the photoconductive emitter must be masked (a). Analogous to the interdigitated photoconductive emitters, destructive interference in a photo-Dember emitter is addressed by breaking the lateral symmetry of the opaque stripes through a thickness variation of the metal (b).
    Recent developments in high-repetition-rate femtosecond sources of terahertz radiation show promising improvements in efficiency, suggesting that photoconductive emitters will...
    May 1, 2011
    (Courtesy of H. Tao et al. [2])
    FIGURE 1. Unit cell of a terahertz absorber, with electric resonator element on top of a polyimide spacer, and a cut wire on a gallium-arsenide substrate at bottom for magnetic coupling (a). Experimental absorption results in blue compared with simulation results in red (b).
    Like the laser half a century ago, metamaterials sometimes seem to be a solution looking for a problem. Now developers are working on a first round of applications in niches that...
    May 1, 2011
    (Illustration courtesy of X. Gu et al. [6])
    FIGURE 1. In the XFROG apparatus a sum-frequency-generation crystal cross-correlates the two pulses. The crystal is angle-dithered to generate the sum frequencies of all frequencies in the continuum (top). In this example of measured and retrieved XFROG traces of an ultrabroadband continuum with a TBP of >1000, the retrieved trace does not agree with the measured trace, indicating that something is wrong. In this case, what’s wrong is not the measurement but the train of pulses being measured: Every pulse in the train is different, violating the universal scientific-measurement assumption that all objects averaged over during a measurement are identical. Fortunately, the XFROG measurement reveals this fact at the same time that it yields a typical pulse in the train (middle). The measured continuum pulse is also shown in the time and frequency domains (bottom).
    Techniques for measuring simple ultrashort laser pulses are often unable to temporally characterize extremely complex pulses—such as shaped pulses, ultrabroadband continua, and...
    May 1, 2011
    FIGURE 1. A conceptual drawing shows a hyperspectral camera today (a) and a new integrated system (b) in which an objective lens is combined with the image sensor and a hyperspectral filter structure that is directly post-processed on top of the image sensor.
    To enable the transfer of applications from the lab to the industry, a new hyperspectral camera module based on CMOS-compatible production techniques has been developed that eliminates...
    May 1, 2011
    (Courtesy of Harvard University)
    Isotope-ratio measurements can be used to distinguish between different sources of carbon in the atmosphere. A precision better than 1‰ is needed for accurate measurements, and the integrated-cavity-output spectroscopy (ICOS) instrument is capable of 0.1‰ precision for a 200 s measurement time period.
    The dramatic decrease in Arctic sea ice in the summer of 2007 was not predicted, and according to some scientists, not well characterized in scientific models.
    May 1, 2011
    FIGURE 1. Electromagnetic near-field distributions are calculated for a silver disk with elliptical cross-section, as schematically depicted in the right inset. Different distributions correspond to different surface-plasmon resonance states of the system, illustrating strong local electromagnetic-field gradients.
    Even as we seek smaller and faster chips to run our computers, we are rapidly approaching fundamental limits of conventional semiconductor electronics. One possible solution is...
    May 1, 2011
    Pennwell web 400 257
    The choice of infrared optical material for an asphere determines how it can be fabricated; this in turn determines which design options are available, such as the addition of...
    May 1, 2011
    An integrated optical magnetic-field sensor consists of a Mach-Zehnder interferometer on LiNbO3 with a doubly loaded loop antenna. It has a frequency response ranging from 2 kHz to 9 GHz (a) and a dynamic range of 98 dB (b).
    Magnetic-field sensors that measure the magnetic portion of electromagnetic fields (as opposed to sensors that measure static magnetic fields) are valuable for determining problems...
    May 1, 2011
    A grayscale diagram shows the results of NIST randomness tests done on a bitstream produced by a SLED-based true random-number generator (RNG) including a time-delayed XOR operation. The chart gives the number of failures out of 1000 trials for the different tests (the one exception is for the random-excursion variant test, which shows results for 561 trials). The RNG passed all tests.
    A true random-number generator (RNG) developed by a group of Chinese and American researchers can generate two simultaneous, independent 10 Gbit streams of random bits from a ...
    May 1, 2011
    (Courtesy of NIICT)
    A seven-core optical fiber carries 15.6 Tbit per core, for 109 Tbit/s through the entire fiber before forward-error correction.
    Demonstrations of high-speed fiber-optic transmission reached a major milestone at the March 10 postdeadline session of this year’s Optical Fiber Communications Conference.
    May 1, 2011
    (Courtesy of the University of Shanghai for Science and Technology and Swinburne University of Technology)
    In the normal Doppler effect (a) for materials with refractive index greater than zero, the detected frequency f’ for a wave source moving toward the detector is shifted to shorter wavelengths (blue shift), and red-shifted for a source moving away. The opposite shift occurs (b) for a negative-refractive-index metamaterial—the inverse Doppler effect.
    When a wavelength source and an observer are moving in relation to each other, a fundamental frequency shift is observed called the Doppler effect due to wave compression or extension...
    May 1, 2011
    (Courtesy of Zhanshan Wang)
    The thermal absorption of fused-silica substrates were measured before cleaning (a), after cleaning using process 1 (b), and after cleaning using process 2 (c). As can be seen, process 2 was more effective.
    Manufacturing a functional high-power laser optical component requires great care in every step. Even a flawless optical substrate is of no use if it hasn’t been cleaned adequately...
    May 1, 2011
    Pennwell web 90 86
    In the years since the laser was invented, some serious resources have been focused on understanding the science and application of light, so that photonics now brings us—along...
    May 1, 2011
    1304qa Chang New
    Can you offer some suggestions on how to bridge the ‘valley of death’ gap startup companies face?
    May 1, 2011
    As I dimly recollect from my childhood readings of assorted European mythical tales, the trolls were mischievous little people who amused themselves by playing practical jokes...
    May 1, 2011