Number 37 (Story #1), June 5, 1991 by Phillip F. Schewe and Ben Stein TRANSPARENCY IN GASES CAN BE INDUCED with lasers. Stephen E. Harris of Stanford (415-497-0224) and his colleagues use "population trapping" to make strontium gas transparent to light that is normally absorbed (Physical Review Letters, 20 May 1991). In this process, discussed by theorists for years but not until now applied to gases, the absorption of laser light---corresponding to the transition of atoms from their ground state into an excited state---is inhibited by destructive interference of the laser light with light at a second wavelength corresponding to a transition from an intermediate energy state to the upper excited state. Thus strontium was made transparent to light at a wavelength of 337 nm by imposing a second beam at a wavelength of 570 nm. Harris believes the technique can be applied to materials other than gases. (Science News, 1 June 1991.)