Chirality Turns the Casimir Force Repulsive

A popular approach for the 3D printing of metals is to pass a laser spot over a layer of powder, which then melts and fuses together. The printer repeats that process for additional layers of powder to build up the desired part. The higher the density of laser power, the faster the printing process. The problem is that intense laser illumination can also introduce gas pockets into the material and degrade the mechanical properties. Just what constitutes too high a laser power density has been a matter of trial and error until now. By imaging with synchrotron x rays the formation of vapor pockets in irradiated metal, Anthony Rollett of Carnegie Mellon University, Tao Sun of Argonne National Laboratory, and their colleagues have found a simple rule to prevent laser-induced defects.