Peter Pitirimovich Sorokin: Laser pioneer dedicated to understanding, creating, and using light

Peter Pitirimovich Sorokin, a renowned pioneer in laser science, passed away on September 24, 2015, from injuries suffered during a fall a month earlier. Peter, an IBM Fellow emeritus, devoted his career to understanding, creating, and using light. His 1966 discovery of laser action in organic dyes is extraordinarily significant. Dye lasers, with their continuous tunability over a broad spectral range, led to a revolution in optical spectroscopy and nonlinear optics. In laboratories throughout the world, dye lasers have been put to use in fundamental studies in physics, chemistry, biology, and medicine. The breadth and significance of this advance may be gauged by the scientific literature: a conservative estimate of the number of papers published, in which results are derived from the use of dye lasers, runs into the tens of thousands. For his discoveries, Peter was honored with the Franklin Institute’s Albert A. Michelson Award, the Optical Society of America’s R. W. Wood Prize, the National Academy of Sciences’ Cyrus B. Comstock Prize, the Technion’s Harvey Prize, and the American Physical Society’s Arthur Schawlow Prize in Laser Science. He was a Fellow of the American Physical Society and the Optical Society of America, and a Member of the National Academy of Sciences.

Peter Pitirimovich Sorokin. Image courtesy of the IBM Corporation.

Peter was born on July 10, 1931, in Boston, Massachusetts, the son of Pitirim Aleksandrovich Sorokin and Elena Baratinskaya Sorokin. He grew up in Winchester, Massachusetts and attended Harvard University, where he received a Bachelor of Arts in 1952 and a doctorate in Applied Physics in 1958. For his doctoral thesis research, under Nicolaas Bloembergen, Peter created an innovative NMR technique for measuring chemical shifts in cesium halides.

Peter joined IBM in 1958, expecting to continue his research on NMR, but a new challenge was on the horizon, one that would change physics and Peter’s career forever. In December 1958, Charles Townes and Arthur Schawlow published a paper in Physical Review, describing how an optical maser (later named the laser by Gordon Gould) might be achieved (1). This paper initiated a global race to build the first working laser. Peter jumped in, conceiving that calcium fluoride crystals, doped with either uranium or samarium, might function as laser media, with total internal reflection providing feedback for stimulated emission. The race was won by Theodore Maiman at Hughes Research Labs in Malibu, California, whose ruby laser used a bright flashlamp to excite chromium atoms in a ruby crystal. Maiman’s laser, elegant, simple, and amazingly powerful, led Peter and his IBM colleague, Mirek Stevenson, to switch from their more elaborate approach to a flashlight-pumped crystal rod design. In November 1960, just two weeks after moving from an IBM building in Poughkeepsie, New York, to the brand new IBM Thomas J. Watson Research Center in Yorktown Heights, New York, Peter and Mirek flashlamp-pumped a cryogenically cooled crystal of uranium-doped calcium fluoride. The crystal lased, becoming the second laser on record. Soon afterward, their samarium-doped crystal lased as well, the third laser on record. For IBM, these successful experiments provided the fuel for publicizing the initial world-class discoveries emerging from the Watson Research Center shortly after it “opened for business.” For Peter, this marked the beginning of his sustained and fruitful career in laser science.

Peter first became interested in the spectral properties of organic dyes in 1964, when he discovered the saturable-dye Q-switch, the first passive device used to produce “giant” (Q-switched) laser pulses. Such devices are used today in dye laser cavities to produce laser pulses of femtosecond duration. In 1966, he and his colleague John Lankard formed a laser cavity consisting of a solution of the fluorescent dye chloro-aluminum phthalocyanine in ethyl alcohol located between two parallel mirrors. Optically pumping the dye with pulses of red light from a ruby laser, they observed intense infrared laser action. The organic dye laser was born. That same year, Peter and his colleagues made another major discovery, observing stimulated electronic Raman scattering in potassium vapor using a Raman-shifted ruby laser. Peter made major advances in extending the spectral range of light sources, using nonlinear “optical-mixing” in atomic vapors to translate the tunability of dye lasers in the visible regime far into the ultraviolet and infrared regions of the spectrum.

Building on these advances, Peter and his colleagues developed innovative techniques for studying chemical dynamics. With characteristic originality, Peter conceived of an approach for obtaining an entire infrared spectrum with a single laser pulse: time-resolved infrared spectral photography. The method used both dye lasers and stimulated electronic Raman scattering—a neat combination of two of his early discoveries—to initially achieve nanosecond time resolution, later shortened to the femtosecond regime. This technique enabled Peter and his colleagues to examine rapid photolytic reactions of molecules of atmospheric importance.

Aside from his scientific work, Peter loved spending time outdoors. He walked and hiked whenever he could, whether in South Salem, New York, during the 21 years he lived there, or on mountain trails throughout the northeast. Peter also loved spending summers at the family cabin in Canada and could adeptly cut the grass there using a traditional scythe. Peter enjoyed listening to classical music, had a whimsical sense of humor, and laughed easily. He delighted in encouraging his family in all their intellectual and creative pursuits.

Peter was a unique and kind individual who will be missed by his family, friends, and colleagues. He is mourned by his wife, Anita, their children, Elena and Paul, and his brother, Sergei.