NEWTON RINGS

Ultrafast laser ablation is a process (important for a number of industrial and surgical applications) in which a short pulse of laser light heats and removes material from a solid surface. Using 120-fsec laser pulses, researchers at the University of Essen in Germany have observed, for the first time, "Newton rings," the optical pattern set up when light rays reflecting from the ablating portion of the sample interfere with light reflecting from the remaining material in the back. The rings, imaged in movie form (frames every tenth of a picosecond), reveal information about the temperature, index of refraction, and other properties of the ablating material. The figure shows Newton rings for a variety of samples. This research is reported by Klaus Sokolowski-Tinten in the 6 July issue of Physical Review Letters.