RETROSPECTIVE RETROSPECTIVE

Peter Pitirimovich Sorokin: Laser pioneer dedicated to understanding, creating, and using light Donald S. Bethunea and James J. Wynneb,1

Peter Pitirimovich Sorokin, a renowned pioneer in Physical Society and the Optical Society of America, laser science, passed away on September 24, 2015, and a Member of the National Academy of Sciences. from injuries suffered during a fall a month earlier. Peter was born on July 10, 1931, in Boston, Peter, an IBM Fellow emeritus, devoted his career to Massachusetts, the son of Pitirim Aleksandrovich understanding, creating, and using light. His 1966 Sorokin and Elena Baratinskaya Sorokin. He grew up in discovery of laser action in organic dyes is extraordi- Winchester, Massachusetts and attended Harvard narily significant. Dye lasers, with their continuous University, where he received a Bachelor of Arts tunability over a broad spectral range, led to a revolu- in 1952 and a doctorate in Applied Physics in 1958. tion in optical spectroscopy and nonlinear optics. In For his doctoral thesis research, under Nicolaas laboratories throughout the world, dye lasers have Bloembergen, Peter created an innovative NMR tech- been put to use in fundamental studies in physics, nique for measuring chemical shifts in cesium halides. chemistry, biology, and medicine. The breadth and Peter joined IBM in 1958, expecting to continue his significance of this advance may be gauged by the research on NMR, but a new challenge was on the scientific literature: a conservative estimate of the horizon, one that would change physics and Peter’s number of papers published, in which results are career forever. In December 1958, Charles Townes derived from the use of dye lasers, runs into the tens and Arthur Schawlow published a paper in Physical of thousands. For his discoveries, Peter was honored Review, describing how an optical maser (later named with the Franklin Institute’s Albert A. Michelson the laser by Gordon Gould) might be achieved (1). Award, the Optical Society of America’s R. W. Wood This paper initiated a global race to build the first Prize, the National Academy of Sciences’ Cyrus B. working laser. Peter jumped in, conceiving that cal- Comstock Prize, the Technion’s Harvey Prize, and cium fluoride crystals, doped with either uranium or the American Physical Society’s Arthur Schawlow Prize samarium, might function as laser media, with total in Laser Science. He was a Fellow of the American 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, sim- ple, 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 mov- ing 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 crys- tal 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 ini- tial world-class discoveries emerging from the Watson Research Center shortly after it “opened for business.” For Peter, this marked the beginning of his sustained Peter Pitirimovich Sorokin. Image courtesy of the IBM Corporation. and fruitful career in laser science.

aIBM Almaden Research Center, San Jose, CA 95120; and bIBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598 Author contributions: D.S.B. and J.J.W. wrote the paper. The authors declare no conflict of interest. 1To whom correspondence should be addressed. Email: [email protected].

12–13 | PNAS | January 5, 2016 | vol. 113 | no. 1 www.pnas.org/cgi/doi/10.1073/pnas.1523215113 Downloaded by guest on September 30, 2021 Peter first became interested in the spectral prop- entire infrared spectrum with a single laser pulse: erties of organic dyes in 1964, when he discovered the time-resolved infrared spectral photography. The saturable-dye Q-switch, the first passive device used method used both dye lasers and stimulated elec- to produce “giant” (Q-switched) laser pulses. Such tronic Raman scattering—a neat combination of two devices are used today in dye laser cavities to produce of his early discoveries—to initially achieve nanosec- laser pulses of femtosecond duration. In 1966, he and ond time resolution, later shortened to the femtosec- his colleague John Lankard formed a laser cavity con- ond regime. This technique enabled Peter and his sisting of a solution of the fluorescent dye chloro- colleagues to examine rapid photolytic reactions of aluminum phthalocyanine in ethyl alcohol located molecules of atmospheric importance. between two parallel mirrors. Optically pumping the Aside from his scientific work, Peter loved spend- dye with pulses of red light from a ruby laser, they ing time outdoors. He walked and hiked whenever he observed intense infrared laser action. The organic could, whether in South Salem, New York, during the dye laser was born. That same year, Peter and his 21 years he lived there, or on mountain trails through- colleagues made another major discovery, observing out the northeast. Peter also loved spending summers stimulated electronic Raman scattering in potassium vapor using a Raman-shifted ruby laser. Peter made at the family cabin in Canada and could adeptly cut major advances in extending the spectral range of the grass there using a traditional scythe. Peter light sources, using nonlinear “optical-mixing” in enjoyed listening to classical music, had a whimsical atomic vapors to translate the tunability of dye lasers sense of humor, and laughed easily. He delighted in in the visible regime far into the ultraviolet and infrared encouraging his family in all their intellectual and regions of the spectrum. creative pursuits. Building on these advances, Peter and his col- Peter was a unique and kind individual who will be leagues developed innovative techniques for studying missed by his family, friends, and colleagues. He is chemical dynamics. With characteristic originality, mourned by his wife, Anita, their children, Elena and Peter conceived of an approach for obtaining an Paul, and his brother, Sergei.

1 Schawlow AL, Townes CH (1958) Infrared and optical masers. Phys Rev 112(6):1940–1949.

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