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The preliminary results of several on-going AGN programs using the 2.16-m telescope at Xinglong Station of Beijing Astronomical Observatory are described. About 150 new AGNs including QSOs, BL Lac objects, and Seyferts have been discovered in the last two years.

It is well known that the three-dimensional dimension of laser speckle is a critical parameter in laser holographic interferometry, laser speckle photography, and holospeckle interferometry. In this paper a statistical analysis for computing the three-dimensional dimension of laser speckle is presented. Explicit formulas have been derived for laser speckle in a free space from a circular scattering area along with some supporting results from an experimental investigation.

The theoretical basis of the new technique called "holospeckle interferometry" is laid out. Several schemes for this new technique are presented along with demonstrations showing its various applications.

A new holospeckle interferornetric technique is developed for visualizing two dimen­ sional velocity field of solids and fluids. The method requires only single exposure and results in sine function fringes representing velocity contours.IntroductionA number of optical methods have been developed for the measurement of velocity field. The most popular seems to be the laser-Soppier anemometry 1 which gives pointwise data. Holographic interferometry yields whole-field information in terms of fringe patterns. In a particular ^arrangement, the fringes depict one velocity ^component from each recording arrangementz . The scattered light laser speckle method~ is effective in measuring 2D velocity. However, at the present state of art, the method can only be applied to slow flows due to the low scattering efficiency along the viewing direction (which is normal to the beam). A newly developed double-exposure holospeckle method alleviates this difficulty by combining holography and speckle interferometry.In this paper, we present a single-exposure holospeckle technique for the visualization of velocity field. Although only sine fringes (whose contrast is low at higher orders) are generated, the method's advantage lies in its economic usage of light energy and avoidance of double exposure.Optical arrangement of methodA schematic of the optical arrangement is as shown in Fig. 1. It is the same as that used in Ref. 4. A section of the moving light scattering medium, situated at the front focal plane of the first FT (Fourier transform) lens, is back illuminated by a collimated laser beam. At the back focal plane the spectrum of the spatial frequency of the scattering wavelets is recorded together with a reference beam by a photographic plate. At this state it is nothing but a lens Fraunhofer hologram. After processing this hologram is placed back at its original position and illuminated by the reference beam for reconstruction. A second FT lens, situated at a focal distance away, converts the reconstructed virtual image into a real one at its back focul plane. Similar to the full-field filtering arrangement of a specklegram, a small aperture is erected at the spectrum plane to select the desired spatial frequency (or the observation direc­ tion) to be calculated by the second field lens for image formation. It shall be shown in the following that this image is modulated by a pattern of velocity contours.Theoretical analysisThe complex amplitude of the wavelets at the section dissected by the first field lens can be expressed as, at time t

Holographic fringe formation and localization are studied using statistical optics in terms of speckle movement and average speckle size. The concept is useful in the application of holospeckle interferometry studies such as three dimensional crack tip deformation measurement.