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The East African Orogen formed as a result of collision between portions of East and West Gondwanaland as the Mozambique Ocean closed in Late Neoproterozoic time, but it is not known exactly when. We use distinctive chemical and isotopic composition of deformed 'schistose' dykes in southern Israel to argue that this collision occurred after about 630 Ma,… (More)

- A Basu, J M Ballantyne
- Applied optics
- 1979

A simple method is proposed for studying the spectral response of a first-order waveguide grating filter with random fluctuations in the period of the grating. The method can be applied to any grating groove shape, and it can be used to study the effect of both random and systematic variations in other grating filter parameters. The numerical calculations… (More)

- A Basu, J M Ballantyne
- Applied optics
- 1979

A study of second- and higher-order waveguide grating filters is considerably complicated by the fact that the coupling between the guided waves and the radiated waves has to be taken into account. In this paper, we review the theoretical calculations of the spectral response of these grating filters that have been reported by several authors and present a… (More)

- Alex Basu, Fikret Mamedov
- 2015

- B S Verma, A Basu, R Bhattacharyya, V V Shah
- Applied optics
- 1990

The inverse transmittance (1/T) of a quarterwave all dielectric multilayer stack is expressed as a mixed series in sinø and cosø, where ø = (pi/2)[(lambda - lambda(0))/ lambda] and lambda(0) is the reference wavelength. This expression has been used to design achromatic beam splitters for the visible and near IR regions having different reflectance (R) to… (More)

- M Kar, B S Verma, A Basu, R Bhattacharyya
- Applied optics
- 2001

Southwell's analysis of optical multilayers within the limits of very thin films has been extended to include absorption in the multilayer for predicting the effective values of the refractive index n(e) and extinction coefficient k(e) of mixed-composition binary homogeneous films over a wide spectral region, including the high-absorption (k > 10(-2))… (More)

- B S Verma, A Basu, R Bhattacharyya, V V Shah
- Applied optics
- 1988

A converted characteristic matrix method has been used to derive a generalized expression for reflectance R (for wavelength lambda at normal incidence) of an all-dielectric multilayer stack consisting of K layers of refractive indices n(1),n(2),n(3)... n(k-1),n(k) having quarterwave thicknesses at the monitoring wavelength lambda(0). The expression thus… (More)

- A Basu, B S Verma, M Kar, R Bhattacharyya, V V Shah
- Applied optics
- 1988

Results of the theoretical computations of reflectance and transmittance values of periodic dielectric multifilm stacks with symmetrical periods, each consisting of films of three different refractive indices, are reported. The analysis yields good estimates of the bandwidths of the low reflectance and high reflectance zones for different compositions of… (More)

Soils of the 62-cm deep Apollo 16 double drive tube 60013/14 are mature at the top and submature at the bottom. Modal analyses of 5529 grains from the 90-150 micrometers and the 500-1000 micrometers fractions from 12 levels of the core show that, in general, agglutinate abundance increases somewhat monotonically to the top and mimics the Is/FeO profile. … (More)

- A Basu, J M Ballantyne
- Applied optics
- 1979

A series of careful and systematic measurements is made to determine the reflection, transmission, and radiation loss coefficients of second- and third-order waveguide grating filters, and the dependence of these coefficients on the wavelength of the incident light. The experimental measurements are found to agree very well with results of calculations made… (More)

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