Compact disks in their existing form may soon be superseded. Current CD technology uses near-infrared laser diodes to read information, because they are long-lived and reliable. But blue would be much better than red. Because the size of a focused spot scales as the square of the wavelength, reducing the wavelength by a factor of two would increase the storage capacity by a factor of four. No wonder there is a concerted effort to produce a current-injected blue laser diode for continuous wave (c.w.) operation at room temperature. Last month in Applied Physics Letters, Naka-mura et al. of Nichia Chemical Industries reported the first successful c.w. operation of a blue laser diode made from gallium-nitride-based materials.
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