Terahertz rays have proved hard to generate cost-effectively, as solid-state lasers so far have been unable to produce terahertz rays without supercooling. Some physicists even have speculated that frequency and temperature are linked by some fundamental physical law. But a team of researchers at MIT and at Sandia National Laboratories in Albuquerque, N.M., have reported a solid-state terahertz laser that operates at nearly twice the temperature that such a fundamental law would have allowed. Although the reported temperature is still too low to enable airport scanners or bomb-detecting devices, the breakthrough is a major step forward in the search for room-temperature terahertz lasers. In the new gallium arsenide and aluminum gallium arsenide laser, the applied voltage causes electrons to jump into an even higher energy state than usual. Scattering allows the electrons to release some energy as physical vibration rather than as light; most of the rest is emitted as photons. To build the laser, the gallium arsenide and aluminum gallium arsenide are deposited in alternating layers; each energy loss occurs in a different layer, and the layer’s thickness is what determines how much energy the electron will lose. The work was published online in Nature Physics on Dec. 12, 2010.