We report on the fabrication and characterization of broadband Bragg filters in microfabricated AlGaAs waveguides. Electron-beam lithography and chemically assisted ion-beam etching were used to fabricate first-order gratings with 250 nm period. Bragg filters with rejection bandwidth ∼15 nm and centered at ∼1.6 μm are demonstrated.

We report all-optical switching with low-peak power in a microfabricated AlGaAs waveguide operating at 1.6 mu m. We show that by using a 1-cm long microfabricated strongly-guided waveguide with 0.8 mu m by 0.9 mu m mode cross-sectional area, switching is achieved with an average power of 1.2 mW for 82-MHz mode-locked 430 fs pulses. The estimated peak pump power and pulse energy inside the microfabricated waveguide were similar to 30 W and similar to 14.6 pJ, respectively, which is 5-10 times lower than the values needed with conventional waveguides. In terms of a practicality index defined via switching power times waveguide length, this waveguide has around the best value.

Single-mode distributed feedback (DFB) laser diodes typically require a two-step epitaxial growth or use of a corrugated substrate. We demonstrate InGaAs-GaAs-AlGaAs DFB lasers fabricated from a single epitaxial growth using lateral evanescent coupling of the optical field to a surface grating etched along the sides of the ridge. A CW threshold current of 25 mA and external quantum efficiency of 0.48 mW/mA per facet were measured for a 1 mm cavity length device with anti-reflection coated facets. Single-mode output powers as high as 11 mW per facet at 935 nm wavelength were attained. A coupling coefficient of at least 5.8 cm/sup -1/ was calculated from the subthreshold spectrum taking into account the 2% residual facet reflectivity.<>

The fabrication and optical performance of Laterally-Coupled Distributed Feed-Back (LC-DFB) lasers were investigated. This device differs from a conventional DFB laser in that the grating does not extend inside the laser ridge, rather, gratings adjacent to a single ridge are used to couple to the fringing fields of the active region. This structure allows the entire laser epi-layer structure to be grown in asingle step thus eliminating any regrowth steps. A recent design with 1.5 mm cavity length and CAIBE-defined ridges and gratings resulted in pulsed single-mode operation up to 36 mW at 937 nm with as-cleaved facets. The light-current characteristic of this device demonstrated a threshold current of 15 mA and a sidemode suppression ratio of greater than 30 dB. The spectral temperature sensitivity was 0.65A@?/^oC for this LC-DFB. Also a CW threshold current of 25 mA and an external quantum efficiency of 0.48 mW/mA per facet were measured for a 1 mm cavity length device with anti-reflection coated facets. Fabrication processes and optical characterization are discussed.

Results are presented on laterally-coupled distributed feedback (LC-DFB) ridge laser diodes. The epitaxial regrowth required in most distributed feedback devices is eliminated by using lateral evanescent coupling of the field to gratings etched along the sides of the ridge. A pulsed singlemode output power of 36mW per facet was achieved at 937.5nm with a sidemode suppression ratio (SMSR) of 30 dB for a 1.5mm cavity length. A pulsed threshold of 11mA, slope efficiency of 0.46 mW/mA per facet, and temperature sensitivity of 0.63angstrom/degrees-C were measured for a 250 mum cavity length LC-DFB.

A TiN(0)-encapsulated copper structure was made by annealing a Cu-10 at%Ti alloy film evaporated on a SiO2/Si(100) substrate in N2 or NH3 ambiente. During thermal cycling, the tensile stress in the nitridated films is in the range of 200 to 800 MPa. The stress relaxation depends on the cooling cycle and the presence of interlayer between film and substrate. A fast heating rate (70°C/min.) to 550°C in an NH3 ambient can effectively suppress the formation of Cu3Ti and enhance the TiNx(0) formation near the surface of the copper film. This self-encapsulated Cu structure exhibits good adhesion to SiO2 and oxidation resistance. A fully encapsulated Cu fine line structure can be achieved by annealing a Cu-10at%Ti alloy film in an Ar ambient at 550°C and then in an NH3 ambient at 550°C to form TiOx/Ti5Si3 adhesion layer and TiN(O) layer, respectively.

SUMMARY In a field experiment at Hurley, small areas of old ryegrass sward, known to be infected with ryegrass mosaic virus (RMV) were partially surrounded by newly‐sown Italian ryegrass. The experiment was harvested by mowing on five occasions. Samples of Italian ryegrass taken when it was 11 months old showed a very marked increase in the levels of RMV close to the areas of old sward. Thus, 84% of the Italian ryegrass plants bordering the old sward to the north contained RMV, compared with 63% of plants only 2.7 m away. The corresponding values to the south were 68% and 39%. The much higher values encountered to the north are presumed to be caused by the movement of the mite vector of RMV ( Abacarus hystrix ) in relation to the prevailing wind. Two different mowers were used, a rotary mower and a reciprocating knife mower. We could demonstrate no increase in the level of RMV as a result of mowing from the infected sward and on to the new sowing and could demonstrate no difference in the infection levels as a result of using the different mowers. We conclude that in mown swards migration by the mite is responsible for all or nearly all of very local spread of RMV.

Changes in the population of stem-boring Dipterous larvae (including Oscinella frit) were examined weekly for a year on plots of perennial ryegrass (Lolium perenne cv. S24). The herbage net regrowth rate of these plots and of plots receiving the pesticide, phorate, was also monitored. Herbage net regrowth rates were greatest in April and October. At the same times the differences in net regrowth between treated and untreated plots were greatest, thus indicating the periods of the greatest loss of production due to pest damage to the sward. Populations of stem-boring larvae fell below 100 m−2 for only 4 weeks in the year and were maximal in autumn and early winter. Larval mortality exceeded 50% during the winter period. A correlation was found between larval activity and sward damage.

Linear modals are used to disentangle the effects of several factors on the birth weight distribution of human infants. Parameters of interest include the overall mean and standard deviation, mean weights of infants of ‘low’ and ‘high’ birth weight; and proportions of ‘low weight’ infants. Conclusions vary strongly with the parameter concerned and in some instances are quite surprising.

The design and characteristics of a minilens system for the production of a microprobe of 20 nm diameter at 500 kV are described. The use of the system for microdiffraction is discussed and further potential applications examined.

Abstract Electron microscope studies of dislocation arrangements around SiO2 particles in strained single crystals of copper indicate that there are lattice rotations associated with the structure. These rotations can be seen when the crystal matrix is close to the exact Bragg position. Using a microscope incorporating a Le Poole lens, diffraction patterns can be accurately obtained from an area 3000 Å in diameter. Measurements of Kikuchi line positions on these patterns enable the magnitude and direction of these local lattice rotations to be determined.

The attachment consists of a modified airlock section, specimen stage and specimen holder. Normal microscope facilities are maintained, and an outlet provided for radiation generated within the specimen. A Le Poole lens incorporated in the airlock section allows the illuminating spot to be varied between 0.25 μ and 200 μ. This small illuminating spot has been used for both micro-diffraction studies, and microanalysis of normal transmission specimens.

Previous articleNext article No AccessEnquiry into the Authorship of the Ordinall of AlchimyM. Nierenstein and P. F. ChapmanM. Nierenstein Search for more articles by this author and P. F. Chapman Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Isis Volume 18, Number 2Oct., 1932 Publication of the History of Science Society Article DOIhttps://doi.org/10.1086/346708 Views: 6Total views on this site Citations: 1Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Curtis Runstedler John Gower’s Alchemical Afterlife in Elias Ashmole’s Theatrum Chemicum Britannicum (1652), Neophilologus 104, no.22 (Jul 2019): 263–281.https://doi.org/10.1007/s11061-019-09619-4