Mary Spaeth Biography (1938-)


Theodore Maiman introduced the first working laser to the world in 1960, initiating one of the most intense periods of scientific activity in modern history. Every major think tank in the United States turned its attention toward perfecting and modifying Maiman's machine. Immersed within this flood of optical research was Mary Spaeth who, just six years after Maiman's invention, developed the tunable dye laser.

Spaeth graduated from Valparaiso University and received her master's degreein physics from Wayne State University. During her studies, Spaeth (along with most other scientists at that time) had become frustrated with the monochromatic nature of lasers: lasers could be built to emit different colors, but,once chosen, that color was fixed. It became clear that a tunable laser was needed--a laser whose color could be changed in mid-stream. Peter Sorokin andJ. R. Lankard had, in 1966, shown how certain dyes affected the coloration ofa laser, and it was upon these findings that Spaeth based her design for a tunable laser. Like Charles Townes's maser and Gordon Gould's laser, the puzzle pieces that formed the tunable dye laser had been around for some time; before Spaeth, however, nobody had successfully assembled the pieces.

Spaeth's tunable laser is used primarily to separate isotopes of certain elements, especially uranium and plutonium. Scientists had long known of these elements' potential, but only the enriched isotopes were useful. For years theyhad employed tedious physical means to obtain these enriched isotopes. The tunable dye laser provided a relatively simple and inexpensive means to separate the natural isotopes from the more desirable ones.

With this laser scientists can change the molecular structure of isotopes, that is, atoms of the same element with a different number of neutrons in the nucleus. Due to their unique structure, each isotope absorbs light differently. A colored light can be absorbed by one kind of isotope without affecting another. When an isotope absorbs light, the extra energy changes the shape andsize of the isotope--and with enough energy, its electrical charge. Changingthe electrical charge of only one of two very similar isotopes makes it easier to separate them. Atoms with a negative charge will be attracted to a positively charged plate and vice versa.

Initially the production of enriched uranium and plutonium isotopes was of primary interest to the military, which was trying to mass produce nuclear weapons; the patent for the tunable dye laser, in fact, belongs to the United States Army, for whom Spaeth worked at the time. Since then, the tunable laser has become the primary source for deriving the isotopes used in nuclear reactors. Work on Spaeth's invention has continued, and she herself was named deputy associate director of Lawrence Livermore National Laboratory's Laser Isotope Separation program. Spaeth continues her work at the laboratory today.

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