Absolute two-photon cross section of Rb measured by differential absorption.

We applied a simple, sensitive differential absorption technique to measure the two-photon cross section for the 5(2)S((1/2))(F(g) = 2) ? 5(2)D(5/2)(F(e) = 4) hyperfine transition in (85)Rb [sigma((2)) = (1.2 +/- 0.5) x 10(-18) cm(4)/W].

Simple diffuser for production of laser speckle.

A passive optical element that is a simple, inexpensive, and effective way for producing laser speckle is described. The optical element, a random phase plate, was developed in our laboratory. The statistics of the speckle pattern it produces were measured and are discussed in this paper.