Researchers have examined the brief interval after a laser pulse arrives and before it heats away a material's atoms during laser ablation. Scientists at the University of Essen in Germany studied the effect of a 620-nm, 120-fs laser pulse on materials such as aluminum, gold and gallium arsenide. They discovered an optical pattern known as Newton rings, resulting when light rays from the solid material interfere with light reflecting off the top of the ablated material. The researchers theorized that this suggests that the ablated material travels transparently upward.