SPAETH, Mary, American physicist, b-1940. From the 1970s she has worked in laser dye technology. Whilst at Hughes Aircraft Corp., she developed tuneable dye-lasers which were able to generate a variety of wavelength lights, different monochromatic coloured lasers. Since many different colours were available, diverse applications became feasible. Mary’s other innovations were devices designed for military use, but which proved to be of industrial value as well. An example is the resonant reflector system in bar-code scanners at shop sales points