It is curious that although H. G. Wells had invading Martians use destructive, focused "heat rays" in 1898, and although Einstein laid their theoretical foundation in 1917, lasers weren"t invented until 1960. Perhaps in homage to Wells, our image of lasers often has more to do with weaponry than with the lasers in our printers, compact disc players, grocery stores, and telephone systems. Bell Labs physicists James Harbison and Robert Nahory illuminate (ahem) the quantum principles behind modern semiconductor lasers in far greater and clearer detail than is usual in popular accounts. The result is a first-class introduction to optics, quantum chemistry, and electronics, as well as a guide to the "Age of Optoelectronics" that is just beginning.