A MULTI-WAVELENGTH SEMICONDUCTOR LASER, one which emits light at three separate colors using only a single material, has been achieved at Lucent Technologies. This result is an extension of Federico Capasso's work with cascade lasers (see Updates 322, 359), in which the laser wavelength is determined not by semiconductor chemistry but by the thickness and spacing of a series of tiny semiconductor layers. The present device can emit three different mid-infrared wavelengths simultaneously, making it useful as the basis for a detector of trace gases (e.g., in monitoring pollutants). (Tredicucci et al., Nature, 26 Nov. 1998.)