A study on Maruca vitrata infestation of Yard-long beans (Vigna unguiculata subspecies sesquipedalis).

Globally, Maruca vitrata (Geyer) is a serious yield constraint on food legumes including Yard-long bean (Vigna unguiculata subspecies sesquipedalis). However, there is a dearth of information on its damage potential, distribution and population dynamics in Yard-long beans. In the present study, the level of M. vitrata larval infestation on flowers and pods of Yard-long beans in Sri Lanka was determined with respect to three consecutive cropping seasons, Yala, Off and Maha. Results indicated that larval infestation and abundance varied with developmental stage of flowers and pods, cropping season and their combined interactive effects. Flowers of Yard-long beans were more prone to M. vitrata larval attack compared to pods. Abundance and level of infestation of M. vitrata varied with plant parts, having a ranking of flower buds (highest) > open flowers > mature pods > immature pods (lowest). Peak infestation was observed six and eight weeks after planting on flowers and pods, respectively. Among the three cropping seasons, M. vitrata infestation was found to be higher during Maha and Off seasons compared to Yala. The findings of this study contribute to the identified knowledge gap regarding the field biology of an acknowledged important pest, M. vitrata, in a previously understudied crop in Sri Lanka.

Plasma frequency and dielectric function dependence on doping and temperature for p-type indium phosphide epitaxial films.

The optical properties of p-type InP epitaxial films with different doping concentrations are investigated by infrared absorption measurements accompanied by reflection and transmission spectra taken from 25 to 300 K. A complete dielectric function (DF) model, including intervalence band (IVB) transitions, free-carrier and lattice absorption, is used to determine the optical constants with improved accuracy in the spectral range from 2 to 35 µm. The IVB transitions by free holes among the split-off, light-hole, and heavy-hole bands are studied using the DF model under the parabolic-band approximation. A good understanding of IVB transitions and the absorption coefficient is useful for designing high operating temperature and high detectivity infrared detectors and other optoelectronic devices. In addition, refractive index values reported here are useful for optoelectronic device designing, such as implementing p-InP waveguides in semiconductor quantum cascade lasers. The temperature dependence of hole effective mass and plasma frequency is also reported.

Optical properties of nanostructured TiO2 thin films and their application as antireflection coatings on infrared detectors.

Oblique-angle deposited titanium dioxide (TiO(2)) nanorods have attracted much attention as good antireflection (AR) coating material due to their low n profile. Therefore, it is necessary to better understand the optical properties of these nanorods. TiO(2) nanorods grown on glass and Si substrates were characterized in the visible (0.4-0.8 µm) and infrared (2-12 µm) regions to extract their complex n profiles empirically. Application of these nanorods in multilayer AR coatings on infrared detectors is also discussed. Optimization of graded index profile of these AR coatings in the broad infrared region (2-12 µm) even at oblique angles of incidence is discussed. The effective coupling between the incoming light and multiple nanorod layers for reducing the reflection is obtained by optimizing the effect from Fabry-Perot oscillations. An optimized five-layer AR coating on GaN shows the reflectance less than 3.3% for normal incidence and 10.5% at 60° across the whole 2-8 µm spectral range.