Describe the operation principle in a couple of paragraph. include in your discussion a schematic diagram and some basic formulae. include in your discussion the component required what are their functions and what are the optical parameters involved. mention time scales and dynamical characteristics that are important.

(1) how you wold measure the saturation intensity of homogeneously broadended two-level system?
(2) how to measure the coherent length of a cw laser
(3) how to determine the minimum laser beam width w0 of a laser