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Biographical Memoirs: Volume 83 (2003)

Chapter: Arthur Schawlow

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Suggested Citation:"Arthur Schawlow." National Academy of Sciences. 2003. Biographical Memoirs: Volume 83. Washington, DC: The National Academies Press. doi: 10.17226/10830.
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ARTHUR SCHAWLOW May 5, 1921-April 28, 1999 BY STEVEN CHU AND CHARLES H. TOWNES ARTHUR SCHAW~OW, the ]. G. Jackson and C. ]. Wood Pro- fessor of Physics at Stanforc! University en c! coinventor of the laser, contributed to many aspects of nuclear, atomic, en cl molecular physics. He was awarclecl the ~ 98 ~ Nobel Prize in physics for "contributions to the clevelopment of laser spectroscopy." His early work incluclecl examination of the shapes, raclial charge distributions, en cl moments of nuclei, the first microwave spectroscopy of a free raclical, ant! coauthoring a wiclely usecl text on microwave spectroscopy. After the laser invention he introclucecl many innovative techniques for very-high-precision spectroscopic measure- ments, inclucling new types of two-step spectroscopy of molecules. With Theoclor Hansch, SchawTow proposal the idea of laser cooling atoms in a vapor to extremely Tow temperatures. This new fielcl has progressed to the point where atoms can be coolecl to temperatures of less than lo-6 degrees above absolute zero, en c! where new states of mat- ter have been created. (David Wineland and Hans Dehmelt proposal a closely relatecl iclea in the same year.) His work has had far-reaching effects in physics, chemistry, biology, medicine, communications, en cl many other aspects of mocI- ern technology. 197

98 B I O G RA P H I C A L EMOIRS In aciclition to receiving the Nobel Prize Arthur SchawTow was electecl a member of the National Academy of Sciences and was accorclecl many aciclitional awards and honors, inclucling the National Mecial of Science in 1991. He was one of two people who hacl the distinction of serving as both president of the American Physical Society en cl president of the Optical Society of America. He was also chairman of the Physics Division of the American Association for the Advancement of Science. Arthur L. SchawTow was born in Mount Vernon, New York, on May 5, 1921. His mother, Helen Mason, was from Canada en cl his father, Arthur SchawTow, was an emigrant from Latvia. They mover! to Toronto, Canada, when Arthur the son was only three years oIcI, en cl he was brought up there, though remaining a U.S. citizen. As a youngster Arthur enjoyed! the famous Book of Know~ecige, react about engi- neering en cl science, likocl to tinker, was intriguccl by raclio, en cl built raclio receivers. His intellectual skills were notable, resulting in completion of high school at the age of 16, en c! receipt of a scholarship in science at the University of Toronto. The latter was important because his family hacl no excess funcis, en c! it steerer! him towarc! physics rather than engineering, which he hacl been seriously considering. Arthur very much enjoyocl jazz music, and while at Toronto he playact the clarinet in the Delta Jazz BancI, which he helpecl to organize. This en cl his engineering interests lecl him to record en cl collect jazz records, an avocation he continued during his entire career. This resulted in an extensive jazz record collection that is now in the Stanford University archives. After earning his unclergracluate degree Arthur continued in graduate school at the University of Toronto. His graduate work was interrupted during World War II. After receiving a master's degree in physics he took a job at Research Enter-

ARTHUR SCHAWLOW 199 prises burbling racier equipment for several years. Towarc! the end of the war he began work on his Ph.D. at Toronto with Professor Malcolm Crawford, a spectroscopist of high stanciarcis who was particularly interested! in examining nuclear properties. Working with him. Arthur clevelonecl a O ' 1 goocl unclerstancling of electron interactions with nuclei in atoms, ant! publisher! what he felt was one of his most important papers, on the determination of nuclear size from hyperfine structure. This interest was to show up again when he took a postcloctoral position with me (C.H.T.) at Columbia University. In the 1950s I (C.H.T.) was in the physics department at Columbia University en c! fortunately hac! been given money for a postcloctoral fellowship by the Carbide en cl Carbon Corporation because Helmut ("Hap") Schulz, a creative, blinc! theoretical chemist there, thought my work on micro- wave spectroscopy of molecules might leacl to work with infrared racliation en cl its effect on chemical reactions. The University of Toronto was outstanding in spectroscopy, en c! I knew professors there, such as Harry Welsh, who toIcl me that Arthur SchawTow wouIcl be a goocl person for this postcloctoral position en c! wouic! probably be interested. Several faculty members recommenclecl him very highly, en cl I was glacl that he accepted the position en cl joined me at Columbia University in the fall of 1949. His work at Columbia macle it clear to me that he was unusually capable en cl hacl remarkable intuition en cl insight. I wouIcl have likocl to have seen him in a permanent academic position at Columbia, but another event, though a happy one, unfortunately macle this impractical. My younger sister, Aurelia Townes, had come to New York to stucly voice en cl for a time livecl in our apartment near Columbia. Arthur has often saicl that the very best thing that happened! to him in New York was that he met

200 B I O G RA P H I C A L EMOIRS Aurelia, the first meeting being when my wife, Frances, macle a point of inviting him to clinner en cl introducing the two of them. They were married in 1951, en cl I was clelightecI. We continues! to work together at Columbia, both on research en cl on writing the book Microwave Spectroscopy. I would have wan tell our collaboration to continue, with him on the Columbia faculty, however I was moving into the chair- manship of the physics department at Columbia, en cl potential claims of nepotism macle it impractical for me to be instru- mental in putting my new brother-in-law on the faculty. He accepted a position at Bell Telephone Laboratories in late 1951 en cl left Columbia. The SchawTows hac! three chiTciren, Arthur Jr., Helen, en cl Edith. The family was religious, en cl Aurelia sang en cl concluctecl the choir at their church. Their two daughters, now Helen Johnson en c! Eclith Dwan, have families en c! are in Wisconsin en cl California, respectively. Arthur {r. intro- clucecl a clifficult en cl challenging problem into the family, one on which Arthur Sr. en c! his wife, Aurelia, worker! tire- lessly en cl hopefully. Arthur {r. was autistic, with very little speech ability. Part of the reason the SchawTows accepted a position at Stanford was that Professor Robert Hofstadter there also hacl an autistic chilcl en cl they, the ShawTows en cl Hofstadters, hoped to help each other find solutions to the problem. After his early years Arthur Jr. was put in a special center for autistic inclivicluals, en cl later Arthur Sr. put together an institution to care for autistic inclivicluals in Paradise, CaTi- fornia. This was named the Arthur SchawTow Center in 1999 shortly before Arthur Sr. 's death. Both parents worked intensively towarc! fincling ways for communicating with autistic inclivicluals. One somewhat controversial method on which Arthur Sr. clicl research en cl became well known was for the autistic individual to spell words with a small handheld

ARTHUR SCHAWLOW 20 machine. Arthur en c! Aurelia wrote a chapter in a book Integrating Moderate en c! Severely Hanclicappec! Learners uncler the title "Our Son: The EncIless Search for Help." The two parents spent many weekends at the center in Paradise, en cl in 1991 Aurelia SchawTow cliecl as a result of an automobile accident cluring the long drive from Stanford to see her son at the center. The Arthur SchawTow Center continues to give important service to inclivicluals with autism or relatecl problems en cl their families. In 1961 Arthur left Bell Laboratories to join the faculty at Stanford University, where he remained until he retired to emeritus status in 1996. During this time he embarkocl on his remarkable career cleveloping laser spectroscopy. In aciclition to being an eminent scientist, Arthur was an entertaining lecturer en cl belovecl mentor. He was a jovial en c! friencITy person who enjoyed! his own jokes so much that he wouIcl burst out laughing as he came to the punch lines. He attracted a large group of students en cl postclocs who affectionately caller! him "the boss." While his brilliant insight produced many striking and incisive experiments, and yielded new phenomena and high-precision instruments, his guiding maxim for experimental physics was "keep it simple. " Arthur showered fatherly acivice and maxims to the point where "the sayings of Art SchawTow" became known beyond Stanford's physics department. To a young scientist intimi- ciatecl by information overIoacl he wouIcl say, "To clo successful research, you clon't neec! to know everything, you just neec! to know one thing that isn't known." Art felt that one of the hallmarks of a successful scientist was a ciriving neecl "to find the answer" and toward this goal "anything worth doing is worth doing twice, the first time quick and dirty and the second time the best way you can." Having been infectec! with his charm en c! vision, many of his flock have

202 B I O G RA P H I C A L EMOIRS gone on to make their own significant contributions in science. Arthur's wit and humor became renown. Recognizing that a scientist does his best work on the back of an envelope, he had envelopes with two backs made. They could be bought from Double Think, Inc., a division of Nocturnal Aviation, Art SchawTow Proorietor. The comnanv's motto: "We fly by night." Art was chairing a session of an optical pumping conference in 1959 when Gordon Gould presented a paper entitled "The LASER, Light Amplification by Stimulated Emission of Radiation," thus introducing the acronym that was to soon replace the "optical maser." At the end of the paper Chairman SchawTow could not resist a comment. As Don Nelson of Bell Laboratories recalls, "Beginning with mock solemnity and ending in belly-shaking laughter, Art opined that the laser was likely to be most used as an oscillator and so should be named 'light oscillation by stimulated emission of radiation,' or the LOSER."i Once he gave a physics colloquium at Stanford entitled "Is Spectroscopy Dead?" He began the talk by defining at great length what he meant by "spectroscopy." After this long introduction his colleague at Stanford, Felix Bloch, asked him to define "dead." After a thoughtful pause Art answered, "Dead is when the chemists take over the subject." Art could say this and make the chemists laugh. 1 J a-- For Art, physics was fun and he made it more fun for the rest of us. While president of the Optical Society of America, Art initiated a "turvy-topsy" contest seeking the inverse of a topsy-turvy picture. A turvy-topsy slide was one that can never be presented correct side up. Four prizes were offered: first prize, $ ~ 0, second prize, a copy of SchawTow's latest paper, third prize, copies of SchawTow's two latest papers, honorable mention, a choice of bumper stickers reading "Optics is Light Work," "Spectroscopists Have

ARTHUR SCHAWLOW 203 Seen the Light," "Light Headed? Stop Eating Photons," or "Photons are Phorever." Even SchawTow's amusing jokes and demonstrations have turned into profound contributions. Guided by his postulate that "anything will lase if you hit it hard enough," he and Ted Hansch strove to create the first "edible laser" made out of Jell-O dessert. Working with two flavors per day, they marched through all 12 flavors of Knox-brand {ell-O. Unfor- tunately, none of the gelatin desserts showed lasing action, and Art retreated back to his office, where he ate each of the failures! Eventually he and Ted spiked the {ell-O with sodium fluorescein, a known laser dye, and immediately saw lasing action.2 The news of the almost-edible laser spread rapidly and was eventually published in the IEEE To urn e] of Quan tom Electronics in ~ 971. This experiment stimulated an experiment done by Herwig Kogeinik and Charles Shank at Bell Laboratories, where they irradiated a gelatin film with the interference pattern of two laser beams, making the first distributed feedback laser. This type of laser is now widely used in long-distance optical fiber communications. His well-known demonstration during which he broke a blue Mickey Mouse balloon inside a clear outer balloon with a portable laser (in the shape of a ray gun, of course!) showed us that a beam of light could reach inside an object without puncturing the outer layers resurfaced when lasers were used to repair detached retinas. In a more recent embodiment the concept was used as an application of "optical tweezers," an optical trap fashioned out of a single focused laser beam. This trap, which was invented to hold onto atoms and micron-size particles, has also been used to reach inside a living cell and manipulate an organelle or chromosomes without damaging the cell or nucleus mem- brane. Similar optical tweezers have been used to manipu- late a single molecule of DNA and pull against the force of

204 B I O G RA P H I C A L EMOIRS a myosin molecule fount! in muscle tissue tugging on an actin filament. SchawTow hacl many productive students en cl associates. I (C.H.T.) was clelightec! with our association at Columbia University. The last paper we ever publishecl together was "Infrared en cl Optical Masers,"3 which initiated the laser clevelopment. At Stanforc! University he attracted! many excellent students en cl postcloctoral fellows. Perhaps his closest long-term associate was Theodore Hansch, who with him clic! much innovative work on high-precision spectroscopy. Professor SchawTow cliecl of leukemia on April 2S, 1999, very close to what wouIcl have been his seventy-eighth birthday. He spent his last few months in a wheel chair, gracefully accepting the expected outcome en cl welcoming the visits of friends en cl family. Appropriately, the memorial service, which celebrates! his remarkable life, incluclec! happy music by the Magnolia Jazz Band. Arthur SchawTow was not just acimirecI, he was cherished by those who knew him. He was a great scientist of remark- able modesty, a supportive teacher, a gentle leader, and a caring human being. Arthur SchawTow's thesis research, in close collabora- tion with Professor Malcolm Crawford, lecl him into high- resolution spectroscopy en cl stucly of nuclear characteristics by atomic spectroscopy. His student work produced seven publications, mostly on nuclear spins en cl magnetic move- ments. They incluclecl an important paper on electric fielcl distribution within nuclei. After he came to Columbia Uni- versity to work with me (C.H.T.) on a postcloctoral fellowship his interest and ideas about nuclei continued. This resulted in measurements and interpretation of nuclear quadrupole moments and a publication concerning the effect of nuclear charge distribution on X-ray fine structure. At Columbia he also was deeply involved with microwave spectroscopy of

ARTHUR SCHAWLOW 205 molecules, en c! with some of my students fount! the first microwave spectrum of a free raclical, OH. This initial measurement was critically important in the later search for en c! discovery of OH in interstellar gas cloucis by Allen Barrett, who was one of my students at that time. This was the first molecular microwave racliation founcl in interstellar cloucis. It helpec! open up an important series of discoveries of interstellar molecules en cl molecular masers, OH itself proclucing many powerful masers. I was also pleasecl that Arthur agrees! to coauthor with me the book on Microwave Spectroscopy, published in 1955 by McGraw-Hill. His work on it began at Columbia University but continual nights en c! weekends after he mover! to the Bell Laboratories in 1951. At Bell Laboratories Arthur initially workocl on super- concluctivity, collaborating with others there, inclucling Berncit Matthias, HaroIcl W. Lewis, en cl George DevIin. As a consultant at Bell Laboratories I visited him there on occasion, en cl one clay in the fall of 1957 I mentioner! my icleas about making optical en cl infrared masers (later to be callecl lasers), en cl found he hacl also become interested in this possibility. We put our ideas and efforts together and Art came up with the iclea of using two parallel mirrors as a way of obtaining a single mocle of oscillation. I thought this iclea might have somehow come from his early work at Toronto University on Fabry-Perot interferometers, but he always dis- missecl that as unlikely. After all, I hacl myself workocl with Fabry-Perot systems but somehow missed the idea. Because we felt optical en cl infrared masers clearly shouIcl be patented, en cl I cleciclecl to interpret my own icleas as belonging to Bell Laboratories, from then on we kept the laser iclea as a proprietary secret until a patent was prepared in mid-1958. After this our manuscript on the subject could be circu- latec! en c! it was publisher! in late 1958.

206 B I O G RA P H I C A L EMOIRS Publication of the paper on "Infrarec! en c! Optical Masers"3 stimulatecl a number of efforts to builcl them. The first International Quantum Electronics Conference, helcl in the fall of 1959, was humming with icleas of possible optical transitions that might leacl to the realization of the first laser. Art, along with colleagues Frank Varsani, Dar Wood, Al Clogston, Stanley GeshwincI, en c! Robert Collins et Bell Laboratories, were exploring the optical properties of ruby (Al2O3:Cr3+) en cl were thinking that this material couIcl be a potential cancliciate for a laser. Art's studies of the properties of the narrow Ret en cl R2 resonance lines in ruby4 generated significant interest, but he eventually rejected the R lines as a potential lasing cancliciate at the Quantum Electronics Conference.5 Art was skeptical that a goocl lasing transition couIcl terminate in the ground state, en cl suggested insteacl the near-neighbor pair lines in ruby he hac! also been studying as a means of obtaining a 4-level system.6 In this case Art's intuition provecl wrong. The following year Theodore Maiman user! a flash lamp to excite a lightly clopecl "pink" ruby crystal en cl achieved laser action on the Ret resonance line. Shortly afterward Art en cl his colleagues were able to demonstrate lasing on his cancliciate pair lines with more highly doped ruby using the same type of a flash lamp used by Maiman in his landmark experiment. Art later remarkocI, "I thought I was being clever, but I outsmarted! myself. "7 Art en cl his Bell Laboratories colleagues continual to explore narrow resonance impurity lines in solids and how these lines were affected by strain, magnetic fielcis, tem- perature, and other perturbations. In 1961 he accepted a professorship at Stanford, where he continued these pio- neering studies with his graduate students en cl postcloctoral fellows. His young colleagues incluclecl Roger MacfarIancI, William Yen, Linn Mollenauer, en c! Frank Imbush, who went

ARTHUR SCHAWLOW 207 on to become leaclers in solicI-state spectroscopy in their own right. Other Art SchawTow students, inclucling John Emmett, John Ho~zrichter, en cl Jeff Paisner, became experts in high-energy puisec! lasers, eventually rising to positions of high responsibility at Lawrence Livermore National Labo- ratory. Warren Moos, a postcloc cluring these years, went on to Johns Hopkins University to become a leacler in astro- physics spectroscopy. In the spring of 1970 Theoclor Hansch arrive cl at Stanford, having just finisher! his graduate studies with Peter Toschek. He recalls, "Walking clown the hallway of the second floor of the Varian physics builcling, a futuristic poster on one of the Coors caught my eye. It shower! an enormous laser gun blasting at some attacking rockets in the sky. The caption in bold letters read "The incredible laser." In smaller letters below someone hac! written, "For creclible lasers, see insicle."8 Ted Hansch and, independently, Christian Borde invented Doppler-free saturation spectroscopy, basecl in part on the spectral hole-burning effect (the "Lamb clip") cliscoverec! by Roger MacfarIane, William Bennett, en cl Willis Lamb. With Art's support, encouragement, and council Ted initi- atec! a remarkable series of experiments in which narrow atomic and molecular lines could be observed without the inhomogeneous broadening clue to the Doppler effect. Using a prism-tunecI, single-mocle argon ion laser, TecI, Marc Levenson, en cl Art resolvecl the hyperfine lines of molecular iodine. With a pulsed dye laser that Ted built they were liberates! from working with absorption lines that acciclentally overIappecl the narrow tuning range of existing lasers. TecI, Issa Shahin, en cl Art were able to measure the Doppler-free spectra of the soclium D lines.9 Upon seeing the soclium spectra taken the night before, Art immediately urged, "You have to clo the same with the reel Balmer-oc line of atomic hydrogen."

208 B I O G RA P H I C A L EMOIRS Within a few weeks the same team recorclec! the saturation spectra of the reel Balmer line of atomic hycirogen.~° This quick en cl clirty experiment with atomic hydrogen was to initiate an experimental program that is continuing tociay after three clecacles en cl seven orders of magnitude of spec- tacular improvement. In aciclition to Shahin, other students en c! postcloctoral fellows that further refiner! this measure- ment in these early clays incluclecl Munir Nayfoh, Sin Au Lee, Stephen Curry, Carl Wieman, John Goldsmith, and Erharc! Weber. During this enormously productive period Art introclucecl molecular-state labeling, in which a laser is usecl to prefer- entially pump molecules out of a specific occupier! molecular level. Absorption lines from the labelecl level as measured using a second broacibancl laser were then weakened, as observer! by Mark Kaminsky, R. Thomas Hawkins, en c! Frank Kowalski.~i Following the invention of polarization spec- troscopy by Carl Wieman en cl Tell Hansch, Art en cl his stu- clents user! polarizer! light to label specific angular momentum states.~2~~5 These methods enablecl Art en cl his associates to greatly simplify and then give assignment to the forest of absorption lines in molecular spectra. Other advances cluring this time incluclecl the two-photon Doppler-free spectroscopy of sodium using a CW dye laser with Ted Hansch et al.,~6 near-resonant enhancement of two-photon spectra with Sune Svanberg et al.,~7 observation of quantum beats with Serge Haroche en cl Jeff Paisner,~8 ant! Doppler-free opto-galvanic spectroscopy with James Lawler, Allister Ferguson et al.,~9~20 en cl polarization inter- moclulation spectroscopy with Tell Hansch et al.2i Also cluring this time William Fairbank, Jr., and Gary Klauminzer studied the excited-state absorption spectra of ruby, emerald, and MgO:Cr3+,22 and Fairbank demonstrated that it was possible

ARTHUR SCHAWLOW 209 to use resonance fluorescence to detect a single atom in a laser beam.23 In ~ 98 ~ Arthur SchawTow was namecl co-winner of the Nobel Prize for his many contributions to the clevelopment of laser spectroscopy. In his Nobel lecture "Spectroscopy in a New Light" he listecl 21 of his most significant papers out of the 168 papers he hac! coauthored. Conspicuously absent from this list is a two-page paper published in Optics Com- munications in 1975 entitlecl "Cooling of Gases by Laser Racliation.''24 In their paper Tecl anclArt outlinecl a proposal to cool atoms by surrounding the atoms with light from all sicles, realizing that the atoms wouic! lose kinetic energy by pref- erentially scattering laser light opposing the motion of the atoms clue to the Doppler effect. They macle a rough estimate of the final temperature by assuming that the initial Doppler width of the absorption line couIcl be reclucecl to the natural line width of the scattering transition. In the case of mag- nesium they estimates! that atoms in the vapor phase conic! be coolecl to temperatures of~O.24 K. Their iclea was clemonstratecl by Leo HolIberg, John Bjorkholm, Alex Cable, Art Ashkin, en c! myself (S.C.) 10 years after their publication. In our initial experiments sodium atoms were cooled to temperatures of ~0.24 thousandths of a degree above absolute zero. Progress in this field! clevel- opecl rapicIly en cl by the year 2000 billions of atoms couIcl be laser coolecl to temperatures as low as 300 nanokeIvin at densities greater than 10~3 atoms/cm3. Further cooling by evaporation in magnetic or optical traps has led to the formation of new states of matter: Bose condensates in a cliTute gas en c! degenerate Fermi gases. The fielcl of laser cooling en cl trapping of atoms was recognized with a Nobel Prize in 1997 in recognition of the

210 B I O G RA P H I C A L EMOIRS revolutionary impact of this work on atomic physics, laser spectroscopy, and metrology. An cl in 2001 on the one- huncirecith anniversary of the first Nobel Prize, a Nobel Prize was given to researchers who user! laser cooling en c! atom trapping methods to achieve Bose condensation of a clilute alkali gas. In 1987 Arthur Schawlow succeeclec! in convincing me (S.C.) to leave Bell Laboratories en cl join the faculty at Stanford University. Soon after arriving I settlecl into the enjoyable routine of retreating often into his office to unwinc! en cl discuss what was happening in my laboratory, with physics at large, en cl life in general. During one of these conversa- O a tions I asker! Art why he clic! not even mention his seminal laser cooling paper in his 1981 Nobel lecture. He shrugged in his characteristically moclest en cl self-effacing way, "In 1981 how was I to know it was going to become important?" NOTES 1. D. F. Nelson. A tribute to Arthur Schawlow. In Lasers, Spectroscopy and New Ideas, eds. W. M. Yen and M. D. Levenson, pp. 121-22. New York: Springer-Verlag, 1987. 2. T. W. Hacnsch, M. Pernier, and A. L. Schawlow. Laser action of dyes in gelatin. IEEE Quantum Electr. QE-7~1971~:45. 3. A. L. Schawlow and C. H. Townes. Infrared and optical masers. Phys. Rev. 112 (1958) :1940. 4. F. Varsanyi, D. L. Wood, and A. L. Schawlow. Self-absorption and trapping of sharp-line resonance radiation in ruby. Phys. Rev. Lett. 3 (1959) :544. 5. A. L. Schawlow. Infrared and optical masers. In Quantum Electronics, A Symloosium, ed. C. Townes, p. 553. New York: Columbia University ~~ Or ~ V..V, Press, 1960. 6. A. L. Schawlow, D. L. Wood, and A. M. Clogston. Electronic spectra of exchange-coupled ion pairs in crystals. Phys. Rev. Lett. 3 (1959) :271. 7. A. L. Schawlow. Origins of the laser. In Laser Pioneer Interviews, pp. 40-62. High Tech Publications, Inc., 1985.

ARTHUR SCHAWLOW 211 8. T. W. Hacnsch. From lint edible lasers to new spectroscopy. In Lasers, Spectroscopy, and New Ideas, eds. W. M. Yen and M. D. Stevenson, pp. 3-16. New York: Springer-Verlag, 1987. 9. T. W. Hacnsch, I. S. Shahin, and A. L. Schawlow. High resolu- tion saturation spectroscopy of the sodium D lines with a pulsed tunable dye laser. Phys. Rev. Lett. 27~1971~:707. 10. T. W. Hacnsch, I. S. Shahin, and A. L. Schawlow. Optical resolution of the Lamb Swifr in atomic hydrogen by laser saturation spectroscopy. Nature 235 ~ 1972) :63. 11. M. E. Kaminshy, R. T. Hawkins, F. V., Kowalski, and A. L. Schawlow. Identification of absorption lines by modulated lower- level population: Spectrum of Na2. Phys. Rev. Lett. 36~1976~:671. 12. R. Feinberg, R. E. Teets, T. Rubbmark, and A.L. Schawlow. Ground state relaxation measurements by laser-induced depopulation. J. Chem. Phys. 66 ~ 1977) :4330. 13. R. E. Teets, N. W. Carlson, and A.L. Schawlow. Polarization labeling spectroscopy of NO2. J. Mol. Spectrosc. 78~1979~:415. 14. N. W. Carlson, F. V. Kowalski, R. S. Teets, and A. L. Schawlow. Identification of excited states in Na2 by two-step polarization label- ing. Opt. Commun. 29 ~ 1979) :302. 15. N. W. Carlson, A. T. Taylor, and A. L. Schawlow. Identification of Rydberg states in Na2 by two-step polarization labeling. Phys. Rev. Lett. 45~1980~:18. 16. T. W. Hacnsch, K. C. Harvey, G. Meisel, and A.L. Schawlow. Two-photon spectroscopy of Na 3s-4d without Donoler broadening Win a (:W rive lair. (jut. (:f7mmun. 11 (10741 .F, (). 1 1 0 --a -- -- --I - ------- -or-- ------------- -- I-- - -I-- -- 17. R. T. Hawkins, W. T. Hill, F. V. Kowalski, A. L. Schawlow, and S. Svanberg. Stark effect study of excited states in sodium using two- photon spectroscopy. Phys. Rev. A 15~1977~:967. 18. S. Haroche, T. A. Paisner, and A. L. Schawlow. Hyperfine quantum beats observed in Cs vapor under pulsed dye laser excitation. Phys. Rev. Lett. 30~1973~:948. 19. T. E. Lawler, A. I. Ferguson, T. E. M. Goldsmith, D. T. Jackson, and A. L. Schawlow. Doppler-free intermodulated opto-galvanic spectroscopy. Phys. Rev. Lett. 42~1979~:1946. 20. J. E. M. Goldsmith, A. I. Ferguson, J.E. Lawler, and A. L. Schawlow. Doppler-free two-photon optogalvanic spectroscopy. Opt. Lett. 4~1979~:230. 21. T. W. Hacnsch, D. R. Lyons, A. L. Schawlow, A. Siegel, Z. Y.

212 BIOGRAPHICAL MEMOIRS Wang, and G. Y. Yan. Polarization intermodulated excitation (POLINEX) spectroscopy of helium and neon. Opt. Commun. 37 ( 1981 ) :87. 22. W. M. Fairbank, Tr., T.W. Hacnsch, and A. L. Schawlow. Absolute measurement of very low sodium vapor densities using laser resonance fluorescence. 7. Opt. Soc. Am. 65 ( 1 975 ~ :199. 23. W. M. Fairbank, Tr., G. K. Klauminzer, and A. L. Schawlow. Excited state absorption in ruby, emerald, and MgO:Cr3+. Phys. Rev. 1 1 (1975) :860. 24. T. W. Hacnsch and A. L. Schawlow. Cooling of gases by laser radiation. Opt. Commun. 1 3 ~ 19 75 ~ :68.

ARTHUR SCHAWLOW SELECTED BIBLIOGRAPHY 1949 213 With M. K. Crawford. Electron-nuclear potential fields from hyper- fine structure. Phys. Rev. 76:1310. 1951 With C. H. Townes. Nuclear magnetic moments and similarity between neutron and proton states in the nucleus. Phys. Rev. Lett. 82:268. 1954 With T. M. Sanders, Jr., G. C. Dousmanis, and C. H. Townes. A microwave spectrum of the free OH radical. 7. Chem. Phys. 22:245. 1955 With C. H. Townes. Microwave Spectroscopy. New York: McGraw-Hill. With C. H. Townes. Effect on X-ray fine structure of deviations from a Coulomb field near the nucleus. Phys. Rev. 100:1273. With S. Geller. Crystal structure and quadrupole coupling of cyanogen bromide, BrCN. 7. Chem. Phys. 23:779. 1958 With C. H. Townes. Infrared and optical masers. Phys. Rev. 112:1940. 1959 With D. L. Wood and A. M. Clogston. Electronic spectra of exchange- coupled ion pairs in crystals. Phys. Rev. Lett. 3:271. With F. Varsanyi and D. L. Woods. Self-absorption and trapping of sharp-line resonance radiation in ruby. Phys. Rev. Lett. 3:544. With J. Brosset and S. Geschwind. Optical detection of paramagnetic resonance in crystals at low temperature. Phys. Rev. Lett. 3:548. 1960 Infrared and optical masers. In Quantum Electronics, ed. C. H. Townes, p. 553. New York: Columbia University Press.

214 B I O G RA P H I C A L 1961 EMOIRS With G. E. Devlin. Simultaneous optical maser action in two ruby satellite lines. Phys. Rev. Lett. 6:96. 1964 With W. M. Yen and W. C. Scott. Photon-induced relaxation in excited optical states of trivalent praseodymin in LaF3. Phys. Rev. A 136:271. 1971 With T. W. Hansch and M. Pernier. Laser action of dyes in gelatin. IEEE f. Quantum Electr. QE-7:45. With T. W. Hansch and M. D. Levenson. Complete hyperf~ne structure of a molecular iodine line. Phys. Rev. Lett. 26:946. With T. W. Hacnsch and I. S. Shahin. High resolution saturation spectroscopy of the sodium D lines with a pulsed tunable dye laser. Phys. Rev. Lett. 27:707. With M. S. Sorem and M. D. Levenson. Saturation spectroscopy of molecular iodine using the 5017 A argon laser line. Phys. Lett. A 37:33. 1972 With T. W. Hansch and I. S. Shahin. Optical resolution of the Lamb Swifr in atomic hydrogen by laser saturation spectroscopy. Nature 235:63. 1973 With S. Haroche and J. A. Paisner. Hyperfine quantum beats observed in Cs vapor under pulsed dye laser excitation. Phys. Rev. Lett. 30:948. 1974 With T. W. Hansch, K. C. Harvey, and G. Meisel. Two-photon spectroscopy of Na 3s-4d without Doppler broadening using a CW dye laser. Opt. Commun. 11:50. 1975 With W. M. Fairbank, Jr., and T. W. Hansch. Absolute measurement

ARTHUR SCHAWLOW 215 of very low sodium vapor densities using laser resonance fluorescence. J. Opt.Soc.Am.65:199. With T. W. Hansch. Cooling of gases by laser radiation. Opt. Commun. 13:68. 1976 With M. E. Kaminsky, R. T. Hawkins, and F. V. Kowalski. Identifica- tion of absorption lines by modulated lower-level population: Spectrum of Na2. Phys. Rev. Lett. 36:671. 1979 With T. E. Lawler, A. I. Ferguson, T. E. M. Goldsmith, and D. T. Tackson. Doppler-free intermodulated opto-galvanic spectroscopy. Phys. Rev. Lett. 42:1046. 1980 With N. W. Carlson and A. T. Taylor. Identification of Rydberg states in Na2 by two-step polarization labeling. Phys. Rev. Lett. 45:18.

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Biographic Memoirs Volume 83 contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. For historical and bibliographical purposes, these volumes are worth returning to time and again.

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