Holographic data storage in a DX-center material

We report on the optical storage of digital data in a semiconductor sample containing DX centers. The diffraction efficiency and the bit-error-rate performance of multiplexed data images are shown to agree well with a simple model of the material. Uniform storage without an exposure schedule is demonstrated. The volume sensitivity is found to be ~10(3) times that of LiNBO(3):Fe. The importance of coherent addition of scattered light with diffracted light in holographic data storage is discussed.     

Drag on a fibre in a counterflow air stream

This paper evaluates the drag on the surface of a fibre moving axially in a counterflow air stream. It is assumed that the fibre velocity is very much greater than the velocity of the air stream.     

Coherent combination of high-power, zigzag slab lasers

We demonstrate a scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains. A common master oscillator injects a sequence of multikilowatt Nd:YAG zigzag slab amplifiers. Adaptive optics correct the wavefront of each amplified beamlet. The beamlets are tiled side by side and actively phase locked to form a single output beam. The laser produces 19 kW with beam quality <2x diffraction limited. To the best of our knowledge, this is the brightest cw solid-state laser demonstrated to date.     

Diffractive coherent combining of a 2.5 kW fiber laser array into a 1.9 kW Gaussian beam

Five 500 W fiber amplifiers were coherently combined using a diffractive optical element combiner, generating a 1.93 kW beam whose M(2)=1.1 beam quality exceeded that of the inputs. Combining efficiency near 90% at low powers degraded to 79% at full power owing to thermal expansion of the fiber tip array.     

Exclusive Free Radical Mechanisms of Cellular Photosensitization

In order to determine the specific effects of radical-induced reactions in the absence of complicating excited-state pathways, four different thiohydroxamic esters and their parent molecule, N-hydroxypyridine-2(1H)-thione, have been studied in murine L1210 leukemia cells for their ability to produce photobiological damage. Irradiation (X_exc= 355 nm) of cells in the presence of thiopyridone esters, specific photolytic precursors of sulfur-, carbon- and oxygen-centered radicals, caused toxicity that was unambiguously demonstrated to result from radical photosensitization mechanisms. Cellular morphological changes were observed following irradiation but apoptosis was not found to take place. A good correlation was evident between lipid peroxidation, measured by the thiobarbituric acid method, and phototoxicity, assessed by the trypan blue exclusion assay, indicating that the ester derivatives exert their effects mainly in plasma and/ or subcellular membranes. Irradiation performed under deaerated conditions also induced significant phototoxicity but the effects of deaeration were dependent on the ester used and are discussed in terms of the nature of the primary radical species generated in each case. Irradiation of L1210 cells in the presence of N-hydroxypyridine-2(1H)-thione, a nonspecific, photochemical source of hydroxyl radical, was also found to trigger phototoxicity and lipid peroxidation. However in this case, photodamage cannot yet be definitely attributed to a radical or type II mechanism although the apparent oxygen independence of phototoxicity would indicate that type II contribution is not significant.     

Artificial atom solids based on metal nanocrystals: Formation and electrical properties

Metal nanocrystals can behave as “artificial atoms” due to their diameter-dependent single electron charging energy. Organically passivated nanocrystals with narrow size distributions can self-assemble into ordered arrays, offering the possibility of artificial atom solids with unique collective electronic properties, derived from both the size-dependent electronic properties of the individual nanocrystal cores and the inter-nanocrystal electronic coupling mechanisms. We review our recent progress on probing the electronic properties of artificial atom solids via variable temperature charge transport measurements on laterally contacted arrays of metal nanocrystals, together with development of combined synthesis and processing routes to manipulate these properties.     

Sub-picomole colorimetric single nucleotide polymorphism discrimination using oligonucleotide-nanoparticle conjugates

Oligonucleotide-gold nanoparticle conjugates are employed to demonstrate selective colorimetric discrimination of a cystic fibrosis-related genetic mutation in a model oligonucleotide system. Specifically, three strand oligonucleotide complexes are employed, wherein two probe oligonucleotide-gold nanoparticle conjugates are linked together by a third target oligonucleotide strand bearing the chosen CF-related mutation. By monitoring the solution optical absorption behaviour of the complexes as a function of temperature, melting profiles may be accurately acquired and reproducibly compared. Following this method, fully complementary sequences are successfully distinguished from mismatched sequences, with single base mismatch resolution, for the V232D mutation. To extend the detection sensitivity of this oligonucleotide-nanoparticle conjugate assay, a novel and compact LED-based optical monitoring system capable of sub-picomole level colorimetric SNP discrimination is also demonstrated.     

Formation and characterization of DNA microarrays at silicon nitride substrates

A versatile method for direct, covalent attachment of DNA microarrays at silicon nitride layers, previously deposited by chemical vapor deposition at silicon wafer substrates, is reported. Each microarray fabrication process step, from silicon nitride substrate deposition, surface cleaning, amino-silanation, and attachment of a homobifunctional cross-linking molecule to covalent immobilization of probe oligonucleotides, is defined, characterized, and optimized to yield consistent probe microarray quality, homogeneity, and probe-target hybridization performance. The developed microarray fabrication methodology provides excellent (high signal-to-background ratio) and reproducible responsivity to target oligonucleotide hybridization with a rugged chemical stability that permits exposure of arrays to stringent pre- and posthybridization wash conditions through many sustained cycles of reuse. Overall, the achieved performance features compare very favorably with those of more mature glass based microarrays. It is proposed that this DNA microarray fabrication strategy has the potential to provide a viable route toward the successful realization of future integrated DNA biochips.