High resolution imaging by employing passive and active approaches

This article begins with the discussions on the formation of speckles in the case of non-coherent quasi monochromatic source and of ways to detect them. Prior to this, a brief introduction on the behavior of the atmosphere and its effect on the plane wavefront from a stellar source is presented. The benefit of short-exposure images over long exposure is highlighted with emphasis set on their comparison as well. The data processing methods that are implemented in our institute in order to decipher both Fourier modulus and Fourier phase are described. The salient features of the adaptive optics system that compensates the atmospheric effects on the image in real time are discussed. The article concludes after a brief discussion on certain astrophysical problems that can be targeted using moderate sized telescopes available in India, such as 2.34 meter Vainu Bappu Telescope (VBT), Kavalur, 2 meter Himalayan Chandra Telescope (HCT), Hanley.