M.M. Pradhan

Multiphonon infrared absorption in silicon

Investigations have been carried out on silicon crystals, grown by float zone (FZ) and Czochralski (CZ) methods, of infrared absorption bands using a Fourier transform infrared spectrophotometer. Multiphonon bands are identified in the light of recent theoretical calculations based on the total energy of silicon crystal lattice. Theoretical results of Ihm et al.(1) and Yin and Cohen(2,3) are found to be in good agreement with the experimental observations of multiphonon infrared bands.

Far-infrared characteristics of multi-element interference filters using different grids

Abstract Theoretical expressions for multigrid interference filters consisting of different grids have been determined. These are reported for filters comprising of two-grid, three-grid and four-grid systems. Theoretical equations may be used to calculate transmission and reflection properties of interference filters made of either wire mesh or reciprocal grid type elements. Some combinations have been reported in which spikes in the pass band are reduced. Calculated transmission of a four-grid interference filter is compared with the available experimental data.

The pyroelectric signal from triglycine sulphate

Abstract The pyroelectric signal from triglycine sulphate has been studied by a focussed He-Ne laser beam and a phase sensitive detection method. It is observed that anti-parallel domains give rise to pyroelectric signals of opposite polarity. The pyroelectric signal is zero when the laser spot is in between anti-parallel domains. The intensity of the pyroelectric signal is recorded and the domain structure is determined.

Low Temperature Fourier Transform Infrared Spectroscopic Studies of Hydrogenated Amorphous Silicon Nitride Films

Low-temperature IR absorptance measurements on thin films of hydrogenated amorphous silicon nitride have revealed the existence of different groups such as NH, SiH and SiH2. Although NH stretching vibration is not observed in the IR transmission-absorption measurements at ambient temperature in such thin films, it becomes quite intense in the temperature range of 230 K to 100 K, and its absorptance slowly reduces on further lowering of temperature. Absorptance-temperature curves revealed that the SiH wagging mode and SiH2 bending mode undergo a large variation in absorptance on lowering of the temperature. Low-temperature Fourier transform infrared (FTIR) spectroscopic studies have been found to be very useful for characterisation of the hydrogenated amorphous silicon nitride films.

Five- and six-grid interference filters for far infrared

Abstract Theoretical equations describing the coefficients of transmission and reflection of five-and six-grid interference filters, consisting of identical grids, are reported. Transmission curves of these filters made from metallic meshes, are plotted for the non-diffraction region. It is shown that such filters have high transmission in the pass band and sharp cut off edges.

Far infrared transmission characteristics of multielement reciprocal grid interference filters

Abstract Transmission characteristics of multielement reciprocal grid interference filters are described. Conditions of maximum transmission for interference filters consisting of identical grids or reciprocal grids, have been obtained. Theoretical transmission of three-, four-, five and six-reciprocal grid interference filters, is calculated. It is shown that the sharpness of cut-off edge increases with the number of elements in the interference filters.

Reciprocal grids as low pass transmission filters for the far infrared region

Abstract Use of reciprocal grids as low pass transmission filters for the far infrared region is discussed. Theoretically calculated transmission and experimentally obtained results are compared. It has been shown that sharp cut off filters can be obtained for g = 2πa0. Such filters can be made by vacuum evaporation methods.

Interaction of oxygen and carbon impurities with the multiphonon infrared absorption bands of Silicon at low temperatures

Infrared absorptance measurements of polycrystalline silicon and single crystals of silicon having oxygen and carbon impurities were carried out at low temperatures in the wavelength range of multiphonon infrared absorption of silicon. Peak absorptance and frequencies were measured at temperatures from 10 to 130 K at intervals of 10 K. Absorptance-temperature curves were plotted for multiphonon bands and impurity bands. It has been observed that the three phonon band [2 TO (Γ) + TA (L)] exhibits a resonance-like behaviour with the anti-stretching mode of Si-O at low temperatures.

Pyroelectric detector-modulator and remote transmission

A pyroelectric infrared detector has been modified in such a way that its front electrode is surrounded by a guarded electrode. A high frequency signal applied at the guarded electrode couples in the detector and low chopping frequency infrared signal sensed by the detector superimposes over the high frequency signal. This signal may then be amplified with proper biasing and the modulated signal is transmitted and remotely detected in the usual heterodyne method.

Remote sensing of temperature by a TGS pyroelectric detector

Use of a TGS pyroelectric detector has been made for remote sensing of temperature. Radiant power is measured in terms of electrical quantities. The system is so designed that the ambient conditions do not effect the measurements.