Small signal equivalent circuit for Geiger-mode avalanchephotodiodes

The first small signal equivalent circuit for a Geiger-mode avalanche photodiode (GMAP) is presented. The equivalent circuit is derived from a 20 μm-diameter GMAP with 3 μm virtual guard ring overlap; the photodetector has peak responsivity at 600 nm and a calculated electrical bandwidth of 5.97 GHz     

The Extractable and Bound Condensed Tannin Content of Leaves from Tropical Tree,Shrub and Forage Legumes

The extractable, protein-bound and fibre-bound condensed tannin (CT) concentrations in the leaves of tropical legumes grown in both Colombia and Northern Australia were determined by the butanol–HCl method, whilst extractable CT was also determined by the vanillin–HCl method. With the exception of Senna siamea all species contained CT. The very high CT concentration found in many plants growing in Colombia may have been partly due to soil fertility being much lower at the Colombian than the Northern Australian site. Acacia boliviana , Arachis pintoi , Centrosema latidens , Senna velutina and Gliricidia sepium contained <55 g total CT kg⁻¹ DM, which suggests that they could comprise a reasonable proportion of ruminant diets. All other species grown in South America contained 100–240 g CT kg⁻¹ DM, which suggests that they should only be fed in small amounts as supplements to dilute the CT concentration. Leucaena species and Calliandra calothyrsus grown in Northern Australia contained intermediate concentrations of total CT (60–90 g kg⁻¹ DM). Most species contained 70–95% of total CT as extractable CT, with the exception of Flemingia macrophylla , where 60% was extractable and 40% bound, and Gliricidia sepium , where almost all the CT was bound to protein. Values for Flemingia macrophylla differed between accessions. Extractable CT determined with vanillin–HCl was generally higher than extractable CT determined with butanol–HCl. Three accessions showed negligible (<1 g kg⁻¹ DM) extractable CT with butanol–HCl but 10–12 g extractable CT kg⁻¹ DM with vanillin–HCl. Two accessions showed undetectable levels of extractable CT but substantial levels of protein-bound CT, illustrating the importance of using a bound CT method for identifying forages containing CT. Relative to freeze drying, oven drying of Leucaena species reduced the concentration of extractable CT and increased concentrations of bound CT. The significance of the results for the nutrition of ruminant livestock are discussed, including the possible roles of protein-bound and fibre-bound CT.     

8.8 W diode-cladding-pumped Tm3+,Ho3+-dopedfluoride fibre laser

A maximum output power of 8.8 W was generated from a diode pumped Tm³⁺,Ho³⁺-doped ZBLAN glass fibre laser. The laser operated with a maximum slope efficiency of 36% with respect to the incident pump power. The wavelength was measured to be 2056 nm and some instability was observed in the output     

High-power 1320-nm wafer-bonded VCSELs with tunnel junctions

A new long-wavelength vertical-cavity surface-emitting laser structure is described that utilizes AlGaAs-GaAs mirrors bonded to AlInGaAs-InP quantum wells with an intracavity buried tunnel junction. This structure offers complete wavelength flexibility in the 1250-1650 nm fiber communication bands and reduces the high free-carrier losses and bonded junction voltage drops in previous devices. The intracavity contacts electrically bypass the bonded junctions to reduce threshold voltage. N-type current spreading layers and undoped AlGaAs mirrors minimize optical losses. This has enabled 134/spl deg/C maximum continuous-wave lasing temperature, 2-mW room-temperature continuous-wave single-mode power, and 1-mW single-mode power at 80/spl deg/C, in various devices in the 1310-1340 nm wavelength range.     

Lone‐Pair‐Induced Covalency as the Cause of Temperature‐ and Field‐Induced Instabilities in Bismuth Sodium Titanate

Bismuth sodium titanate (BNT)‐derived materials have seen a flurry of research interest in recent years because of the existence of extended strain under applied electric fields, surpassing that of lead zirconate titanate (PZT), the most commonly used piezoelectric. The underlying physical and chemical mechanisms responsible for such extraordinary strain levels in BNT are still poorly understood, as is the nature of the successive phase transitions. A comprehensive explanation is proposed here, combining the short‐range chemical and structural sensitivity of in situ Raman spectroscopy (under an applied electric field and temperature) with macroscopic electrical measurements. The results presented clarify the causes for the extended strain, as well as the peculiar temperature‐dependent properties encountered in this system. The underlying cause is determined to be mediated by the complex‐like bonding of the octahedra at the center of the perovskite: a loss of hybridization of the 6s² bismuth lone pair interacting with the oxygen p‐orbitals occurs, which triggers both the field‐induced phase transition and the loss of macroscopic ferroelectric order at the depolarization temperature.     

High temperature Fabry-Perot probe interrogated with tunable fibre ring laser

A high temperature fibre-optic based probe is described based on a miniature Fabry-Perot with a maximum operating temperature of ~700degC limited by the gold coated fibre transceiver link connecting the optical source to the probe. It was interrogated by a tunable fibre laser which could be linearly or sinusoidally tuned at scanning rates of 2 and 20 kHz, respectively. The transfer function of the system is in the form of channelled spectra rather than the usual interference fringes observed for interferometric sensors. The periodicity of the channelled spectra fringes is governed by the Fabry-Perot free spectral range which is related to the inverse of the probe temperature.     

Measurement of far-infrared laser frequencies from optically pumped CHD/sub 2/OH

A three-laser heterodyne system was used to frequency measure 11 previously observed optically pumped far-infrared (FIR) laser emissions of CHD/sub 2/OH. These newly measured frequencies have fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/ and correspond to laser wavelengths ranging from 47.8 to 238.0 /spl mu/m. The pump laser offset frequency was measured for 15 CHD/sub 2/OH FIR laser emissions.     

An exact TEM calculation of loss in a stripline of arbitrarydimensions

Based on a modification of a conformal mapping originally introduced by R.H.T. Bates (1956), an exact expression for the quasi-static conductive attenuation constant α_c, of a general stripline with arbitrary dimensions is obtained. The method is based on a quasi-static formula for α_c which assumes a transverse electromagnetic (TEM) mode and is thus restricted to the case where the skin depth is small compared to the strip thickness. The final formula for α_c involves an integral of only a smoothly varying function, since an analytic extraction of a term representing the singular behavior of the charge density is performed in the analysis. A comparison of the results obtained using the present method and the approximate formulas of S.B. Cohn (1955) shows that a maximum error of about 5-6% occurs in the Cohn formulas at a point where the two approximate formulas are joined