| || Laser Optogalvanic Spectroscopy: Experimental Details and Potential Applications in R and D
Author : Reddy, M.N.
Source : Defence Science Journal ; Vol:44(4) ; 1994 ; pp 279-293
Subject : 621.375.826 Laser Science
Keywords : Material characterisation ;Thermionic detection;Positive column discharge;Hollow cathode discharge;Discharge plasmas;Optogalvanic effects
Abstract : Laser Optogalvanic Spectroscopy (LOGS) is an extremely sensitive detection technique based on the 'Optogalvanic Effect'. The impedance change of gaseous discharge following the absorption of resonant laser light by the discharge species has proved to be a powerful spectroscopic tool to investigate all kinds of matter in vapour phase in discharge plasmas and flames. LOGS does not require any optical detector and the signal-to-noise ratios are often greater than 10/sup 3/. The advent of tunable lasers has pushed LOGS as a unique detection technique, efficient over a wide frequency spectrum from UV through visible to IR. As a simple and most sensitive detection technique, LOGS can have diverse practical applications in science and technology. The experimental details with different discharge excitations and the potential applications of LOGS are briefly described. Some prominent practical applications like wavelength calibration, laser linewidth determination, trace element detection, isotope analysis, material characterisation, laser frequency and power stabilisation, Rydberg atom spectroscopy and combustion and plasma diagnostics are briefly discussed.
| || Carbon Carbon Composites: An Overview
Author : Devi, G. Rohini;Rao, K. Rama
Source : Defence Science Journal ; Vol:43(4) ; 1993 ; pp 369-383
Subject : 678 Composite Materials
Keywords : Pseudoplastic behaviour;Inverse composite;Aircraft brake discs;Material characterisation
Abstract : Carbon carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviour. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from several industrial and biomedical applications. The multidirectional carbon-carbon product technology is versatile and offers design flexibility. This paper describes the multidirectional preform and carbon-carbon process technology and research and development activities within the country. Carbon-carbon product experience at DRDL has also been discussed. Development of carbon-carbon brake discs process technology using the liquid impregnation process is described. Further the test results on material characterisation, thermal, mechanical and tribological properties are presented.