Scientists have moved a step closer to achieving a tunable, mid-infrared semiconductor laser, demonstrating an intersubband stimulated emission.A team of researchers from the University of Illinois and the University of Paris conducted tests revealing that emitted photons confined in a testing device long enough induce more emission by other excited electrons. The researchers say this phenomenon could result in the operation of an optically pumped, unipolar solid-state laser. The proposed laser would emit in the mid- to far-infrared, a range of wavelengths above 10 µm that has been accessible only to gas lasers.The new semiconductor design would be tunable to particular wavelengths by changing the thickness and composition of the lasers.