Gravitational micro-lensing effects and astrophysical applications

Some important astrophysical applications of microlensing are discussed. The basic lens equations, which are essential for determining the image properties of the source (either point source or extended source), are presented. In the case of the high-amplification events, the flux factor K and the topological configurations of the critical curves in the n-star field are also discussed. Astrophysical applications, such as the structure of the source (QSOs), cosmological distance (direct determination of the Hubble parameter H0), and the matter density distribution of the deflecting gravitational field, are examined.