Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Phase-locked phase conjugation using a Brillouin loop scheme to eliminate phase fluctuations

Abstract: We describe experiments investigating a technique that uses stimulated Brillouin scattering to phase conjugate a number of laser beams while preserving their relative phases. Phase locking of a number of beams focused into a stimulated Brillouin scattering cell is achieved by four-wave mixing with a pair of unfocused pump beams. The second pump is generated from the first by use of a stimulated Brillouin scattering loop geometry that minimizes phase fluctuations. We show that the reduction in phase fluctuations substantially improves the degree of phase locking. The requirements on four-wave mixing pump intensity are determined. The technique has the advantage of being insensitive to changes in alignment, with the potential to combine coherently a large number of laser amplifiers in a simple and compact geometry.

Performance limitations of surface-machined accelerometers fabricated in polysilicon gate material

Abstract: In this paper we seek to determine the limitations imposed on the sensitivity, dynamic range and bandwidth of surface-micromachined accelerometers by their small masses and spring constants. The dynamic behaviour of a simple sprung mass system is considered to obtain a fundamental model for the accelerometer. The model is then extended to include thermal noise. We describe a prototype accelerometer structure fabricated using CMOS-compatible processing, which exploits the polysilicon gate material for the micromachined device. We apply the model to this simple accelerometer structure to determine the potential performance (range, sensitivity and bandwidth) of surface micromachined accelerometers. We conclude that it should be possible to fabricate an accelerometer with a sensitivity of 0.01 m s−1 using surface-micromachining technology.

Studies of shaped charges with built‐in asymmetries. Part II: Modelling

Abstract: Pour etudier l'influence d'un allumage asymetrique sur un jet de charge creuse, on a utilise une charge creuse bien caracterisee. Les jets de charge creuse ont ete enregistres par radiographie-eclair lors de l'allumage excentrique respectivement a 2, 4, 6, 8 et 10 mm de l'axe central. Ces radiographies ont permis de determiner les vitesses axiales et laterales des particules des jets. Une publication plus ancienne a emis l'hypothese qu'il pouvait exister une relation simple entre les vecteurs de depart des particules de jet et la geometrie de l'onde de detonation arrivant sur le revetement. Chaque element de jet d'une charge creuse allumee asymetriquement part sous un certain angle determine par la difference entre l'angle courant de l'onde de detonation actuelle a l'endroit ou elle entre en contact avec le revetement et l'angle que l'on obtiendrait si l'initiation etait parfaitement axiale. On a mis au point un programme informatique simple qui permet de calculer pour n'importe quelle charge initiee excentriquement les angles instantanes entre le front de detonation et les elements successifs du revetement rencontres par l'onde lorsqu'elle evolue le long de celui-ci. Comme it est possible d'attribuer la vitesse des particules du jet aux endroits du revetement d'ou elles sont parties, on peut calculer simultanement la vitesse axiale et laterale du jet.