Autofocus of imaging ellipsometry

Through polarized light interacting with samples, imaging ellipsometry is capable of aiding in the study of semitransparent biological cells microscopically; it is also possible to find applications in marker-free nondestructive disease diagnosis. Often a living biological cell is sensitive to environmental conditions, and fast measurement is preferred. Fast and accurate locating of the focal plane is important for biosensing. By analyzing our previous published through-focus ellipsometry images for S. mutans cells on Au film, we have found an efficient method of locating the focal plane position, i.e., through edge detection of cells in ellipsometry images. The method is not sample-dependent. As the edges are decided only by a sample's own features, the method is robust against noise or small shifts of images. It is also easy to use without the need to choose a threshold value as in the Laplace filtering method. The method can be further useful for biosensing applications.