RETROSPECTIVE

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

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 extraordi- narily significant. Dye , with their continuous tunability over a broad spectral range, led to a revolu- tion in optical and nonlinear . In laboratories throughout the world, dye lasers have been put to use in fundamental studies in , 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 Peter Pitirimovich Sorokin. Image courtesy of the IBM Corporation. Prize, the National Academy of Sciences’ Cyrus B. Comstock Prize, the Technion’s Harvey Prize, and 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 Physical Society and the Optical Society of America, emission. The race was won by at and a Member of the National Academy of Sciences. Hughes Research Labs in Malibu, California, whose Peter was born on July 10, 1931, in Boston, used a bright flashlamp to excite chromium Massachusetts, the son of Pitirim Aleksandrovich atoms in a ruby crystal. Maiman’s laser, elegant, sim- Sorokin and Elena Baratinskaya Sorokin. He grew up in ple, and amazingly powerful, led Peter and his IBM Winchester, Massachusetts and attended Harvard colleague, Mirek Stevenson, to switch from their more University, where he received a Bachelor of Arts elaborate approach to a flashlight-pumped crystal rod in 1952 and a doctorate in Applied Physics in 1958. design. In November 1960, just two weeks after mov- For his doctoral thesis research, under Nicolaas ing from an IBM building in Poughkeepsie, New York, Bloembergen, Peter created an innovative NMR tech- to the brand new IBM Thomas J. Watson Research nique for measuring chemical shifts in cesium halides. Center in Yorktown Heights, New York, Peter and Peter joined IBM in 1958, expecting to continue his Mirek flashlamp-pumped a cryogenically cooled crys- research on NMR, but a new challenge was on the tal of uranium-doped calcium fluoride. The crystal horizon, one that would change physics and Peter’s lased, becoming the second laser on record. Soon career forever. In December 1958, Charles Townes afterward, their samarium-doped crystal lased as well, and Arthur Schawlow published a paper in Physical the third laser on record. For IBM, these successful Review, describing how an optical (later named experiments provided the fuel for publicizing the ini- the laser by Gordon Gould) might be achieved (1). tial world-class discoveries emerging from the Watson This paper initiated a global race to build the first Research Center shortly after it “opened for business.” working laser. Peter jumped in, conceiving that cal- For Peter, this marked the beginning of his sustained cium fluoride crystals, doped with either uranium or 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].

www.pnas.org/cgi/doi/10.1073/pnas.1523215113 PNAS Early Edition | 1of2 Downloaded by guest on September 24, 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 . Phys Rev 112(6):1940–1949.

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