A team of physicists led by Ramón Corbalán at the Universitat Autònoma de Barcelona has developed a theoretical model that promises to meet one of the great challenges of modern physics: continuous emission of x-ray laser light. According to Corbalán, although the idea exists only on paper and is far from being put into practice, the laser has enormous potential for everything from digital video disc (DVD) technology to microsurgery. A laser within the visible range is fired at a rubidium atom beam contained in a small transparent cube that is placed between two mirrors. The laser and the atom beam can be perpendicular or pointing at each other. In either case, the collision generates a so-called laser without population inversion that has a frequency up to 10 times that of the external laser. Lasers without population inversion are still at an experimental stage, and very few exist. Corbalán's team said they were built mainly to prove that the theory behind them was correct and have served for little else. However, the Spanish team insists that its model is the first to derive a practical application from this technology, and an important one: frequency gain. Scientists have developed a theoretical model of a laser without population inversion that could someday lead to a 100 percent boost in DVD capacity. "Our theoretical contribution in this field has shown that it is possible to generate high-frequency laser light using a laser with a relatively low frequency," said team member Jordi Mompart. One drawback of the model is that the external laser is a gas laser, which is simpler than the semiconductor lasers used in DVD technology. But the theory is a starting point, Mompart said. "At the very least, what we have done -- if it works -- would be a first step so that other people would try the same thing with semiconductor lasers." The stakes are huge. Mompart said that increasing the frequency of lasers used in disc scanners by 20 percent led to the development of DVD from CD technology. Now, a tenfold increase in laser frequency would boost DVD capacity by 100 percent. "The only thing holding back development of DVDs with higher capacity is the lasers," he said.