Ber. Wissenschaftsgesch.42(2019): 375–399www.bwg.wiley-vch.de

DOI: 10.1002/bewi.201900009

Convergence in Cold WarPhysics:Coinventing theMaser in thePostwar Soviet Union*

ClimØrioPaulo da Silva Neto andAlexei Kojevnikov

Summary: At theheightofthe Cold War, in the1950s,the processofparal- lel inventionofmasersand laserstookplaceonthe opposing sidesofthe Iron Curtain.While theAmerican part of thestory hasbeeninvestigatedby historians in much penetratingdetail, comparable Soviet developments weredescribed more superficially.Thisstudy aimsat, to some extent, re- pairingthisdiscrepancy by analyzingthe Soviet path towardsthe maser from acomparative angle. It identifies,onthe onehand, significantdiffer- encesbetween thetwo projectsregardingtheir heuristics, therelationship between theory andexperiment, groundingindifferentacademic cultures, andthe resultingconceptualizationofthe maserprinciple. At thesame time,the casealsoillustrates more fundamentaltransformationsinthe practicesofpostwar research that can be characterizedasaconvergence between theSoviet andthe American scienceofthe period.

Keywords: maser, quantumelectronics, Cold Warphysics,Soviet science, militarizationofphysics, comparativestudies,AlexanderProkhorov,Nikolai Basov, CharlesTownes

By themid-1950s, afterseveral yearsofrestrictionsoncontactswithWestern sci- entists, Sovietphysicistsgradually resumedtheir participationininternational conferences andbegan to restorecommunicationswithforeign colleagues.1 Alexander MikhailovichProkhorov (1916–2002)travelled to hisfirst conference outsidethe communistpartofthe world in thespringof1955,tothe meetingof

1 Ivanov 2002.

C. P. da SilvaNeto, Assistant Professor, MultidisciplinaryCenterofBarra,Federal Universityof WesternBahia,Av. 23 de Agosto,S/N,Barra, BA,Brazil, 47100-000, E-Mail:[email protected] A. Kojevnikov,Associate Professor, Department of History, University of BritishColumbia, 1873 East Mall,Vancouver,BC, Canada,V6T 1Z1, E-Mail:[email protected] *Earlier versions of this paperwerepresented at theSecondBiennial Early-CareerConferencefor Historians of thePhysicalSciences,the American InstituteofPhysics,College Park,MD, andat theSymposium “QuantumCultures: Historical Perspectives on thePractices of QuantumPhysi- cists” at the25thInternational Congress of History of Scienceand Te chnology.The authorsare thankful to AlexandreBagdonas, Joan Bromberg,OlivalFreireJr. ,JosephMartin, IndianaraSilva, andtwo anonymousreviewers fordiscussions andcommentsonthe manuscript,and to Iuri Popov, KirilA.Prokhorov,and AlexanderK.Prokhorov forsharing theirstories andinformation.One of theauthors,Silva Neto,would like to thankhis doctoral supervisor, Olival Freire Jr., formuchhelp- fuladvice, andhis continuedsupportand encouragement.

 2019 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim 375 ClimØrioPaulo da SilvaNetoand Alexei Kojevnikov

theFaraday SocietyinEngland wherehegaveapresentationonthe “Theoryof theMolecularGenerator.” Prokhorov’sproposalofafundamentallynew kind of electronic device came as abig surprise to anotherparticipant at theconference, theAmericanphysicist CharlesH.Townes (1915–2015),who hadbeeninde- pendently workingonthe same kind of generatorsince 1951. Townes andcollab- oratorscalledtheir apparatusthe MASER(abbreviatedfromMicrowaveAmplifi- cation by Stimulated Emission of Radiation). Townes laterdescribed theepisode as a“revealing,” “eye-opener” encounter, forhehad notknown aboutthe rival Sovietproject.Theoretically, Townes hadmuchtolearn from Prokhorov’sap- proach,but on theexperimentalside, theAmericanteamwas definitely ahead. “After thepresentation,”Townesrecalled, “I gotupand said,Well, that is very in- teresting, andwehaveone of these[generators already]working.”2 Thefactthatessentially thesamedevicewas beinginventedinparallelonboth sidesofthe Iron Curtainatthe height of theCold War, despitehighbarriersfor personal communications andscientificexchanges,could surprise notonlypartic- ipants at the1955conference, butalsomanylater Scienceand Technology Stud- iesscholars whoimbibed Harry Collins’famousmantrathat“no scientistsuc- ceeded in building alaser by usingonlyinformation foundinpublished or other writtensources.”3 TheTownes-Prokhorovepisode,however,was notcompletely exceptionalorunprecedented,but quitesymptomatic of ageneral trend. Physics in theUnitedStatesand in theSovietUnion oftenevolved alongsimilar lines during that period,afact acknowledged by theNobel Committee’sdecisionto award its1964 prizeinphysics jointly to Townes,Prokhorov,and Nikolai Genna- dievichBasov (1922–2001) “for fundamentalworkinthe field of quantumelec- tronics, whichhas ledtothe construction of oscillatorsand amplifiers basedon themaser-laser principle.”Inthispaper,wewillanalyze theSovietphysicists’ path towardsthe co-invention of themaser andargue that,despite politicaldivisions andculturaldifferences,inthisearly period of theColdWar,the practiceofphys- icsinthe Soviet Unionand inNorth Americaunderwent importantrestructuring that made them more similarratherthandistinct. Thelogic of theCold Warconflictand Cold Warhistoriographyhas typically directed scholars to focusprimarily on differences in ordertoemphasize opposi- tionsand contrastsbetween thetwo greatpowersand ideologies. Much less atten- tion hasbeenpaidtothe othersideofthe story: that intensecompetition also en- couraged mutual observation andmanyimportant if unadvertisedimitations, adaptations, andborrowingsoneitherside. Thosewho wroteabout this trend, from JanTinbergentoJohnKenneth Galbraith, to Andrei Sakharov,usually char- acterizedthe resultingstructuralsimilaritiesas“convergence” betweenthe twosys- tems of modern industrial society. 4 Forthe purposes of this study, it is important to emphasizethatthe convergencetheorywas,first of all, adescription of the then existing trends whichbecameparticularlypowerfulduringthe 1960s,and

2 Townes 1999, on 76 –78. 3 Collins1992, on 55. 4 Tinbergen1961. Alreadythe firstbroad sociological studiesonSovietsociety promoted by Ameri- canmilitaryagenciesconcluded that “the Soviet Unionwas astableindustrialsociety,inimportant ways notsodifferentfromthe United States.” See: Engerman 2010, on 399.

376 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics only secondarilyattempted to extrapolate theongoing momentum into long- term predictionsfor thefuture. Thoseconvergingtrendsembraced, besideseco- nomics,manyother aspectsofsocialand politicallife. Forexample,Sovietvalues andinfluencesaffectedsuchimportant developments in theWestasplanningand theregulationofcapitalistmarkets,support forwomen’s equality andlegalization of abortion, acceptance of decolonization andracialequality, multiculturalism andaffirmative action,and greatlyexpandedaccesstohighereducation anduni- versal healthcare. ColdWar sciencewas notexempt; on thecontrary, theprocess of convergence wasmucheasierfor it,because both theAmericanand Sovietsystems,despite theirideologicaloppositions on otherfronts, shared asimilar embraceofscientis- ticand technocratic values.Bothofthemduringthatperiodgranted scienceand technologyunprecedented prestige andgovernmentsupport,especially duetothe 1957launchofSputnik andthe resultingspace race.5 As we will see, converging trends in Soviet andAmericanscience at theheightofthe Cold Warincludednot only intellectualand technological developments,but alsoinstitutional andstruc- turalsimilarities. Thegrowthofinstitutional infrastructure forresearchand developmentrepre- sented onesuchcommontrend beneath theguise of ideologically opposite labels. ThecharacteristicallySovietmodel of sciencebecameestablished in themid- 1930s. Sergei Vavilov, thePresident of theUSSRAcademy of Sciences from 1945 to 1951,described itskey features, including generous governmentfunding,em- phasis on practically useful research,and astructuralorganizationinwhich privi- legedresearchinstituteswithlarge,multidisciplinary teamsofscientists,engineers andtechnicians worked together on thepursuit of goal-oriented research,com- bining basic sciencewithtechnologicalinventions.6 Initially,the Sovietresearch modelcameabout throughacompromise between theBolshevik government andnon-party scientists on thebasis of asharedunderstanding that scienceand technologywerethe key tools necessarytotransform theSovietUnion into amodernstate.7 In theUnitedStates, federalfunding forresearchand develop- ment also graduallybecameanacceptablepracticeduringthe NewDeal. World WarIIand theCold Warfurther transformedAmericanscience in thedirection of what,fromVavilov’sperspective,resembled thesocialist modelofscience,but what in theUnitedStatesbecameknown underamore neutralterm, “big sci- ence.” NotunlikeSovietscientists, many American researchersalsobecameaccus- tomedtostate-sponsored andgoal-oriented projects, thesymbiosis between sci- ence andengineering, collectiveand multidisciplinarywork, andcomplex hierar- chiesinside huge federal, military-funded laboratories, with excessivebureaucratic controls andsecrecy.8 Theatomicbomband theCold Warbrought aboutthe deep militarization of scienceinbothcountries,which reachedits apogee after1950. American and Sovietphysicistswererecruited,orenlistedthemselves, intomassive effortsto

5 Kojevnikov 2008;Wolfe 2012. 6 Vavilov 1948. 7 Kojevnikov 2013. 8 Wolfe2012; Kevles 1990.

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strengthen themilitarycapabilitiesoftheir conflictingstates. Theconsequencesof this symbiosisbetween research andmilitaryestablishmentshas attractedmuch analysis anddebatewithinthe historyofscience over thelastforty years. Paul Forman,inparticular, hasarguedthatthe material cultureand ethosinherited from wartime projectsand thescope of federalsupport forphysics throughmili- tary channels thoroughly transformedthe practice of American physicsasadisci- pline. From theend of WorldWar II throughthe 1960s,theyhelpeddetermine what knowledgequestswereconsideredimportant,achievable, andprioritized. Forman’s analysis also demonstrated thedeepstructuraleffects of military patron- ageonfieldsand topics that remained nominally civilian andunclassified, such as microwavespectroscopyand quantumelectronics (the fieldthatwould eventually encompassall maser- andlaser-related research). Even when researcherssuchas Townes stillbelievedinand proclaimed themselves supporters of theideology of pure science, theirprojects, such as masers or atomic clocks,weredeemedstrategi- callyrelevantfor national defense, relied on military funding, andoften constitut- ed an unclassified tipofthe much larger defense-oriented project pursuedwith thesameequipment within thewalls of thesamelaboratory.9 IanHacking thus called thelaser “a remarkable gift”fromthe Department of Defense,10 aphrasethatsummarizeswellthe role of themilitaryinthe develop- ment of quantumelectronics.Doubtlessly,the military funding, knowledge, and technologycreated in theefforttodevelop radarduringthe war,the skills andex- pertiseacquiredbyphysicistsfrommilitaryprojects, andpostwar programsde- visedbymilitary agencies werecrucial to theinvention of themaser in theUnited States.Hacking’s remark,however,leavesunacknowledgedthe work of scientists in Europe andthe SovietUnion whocontributed to this invention.Inher book TheLaser in America,JoanBrombergadmittedthat“even thehistorian wholooks at theAmericanworkaloneseescontinually theimpactofdevelopmentsin Europe andthe SovietUnion.”11 Severalother authorshavegonesomewhatfur- ther in integratingspecificcontributions of Sovietscientistsintothe generalhisto- ry of masers andlasers,but thegeneral institutionalcontext,practiceand research culturefromwhich theSovietworks emerged, andinparticularits relationship with classified military projectsand funding, have notyet beenproperlystudied in theexistingliterature.12 In this paper, we aimtoanalyze thecoinvention of themaser in theSoviet Unionwhile drawingcomparisons based upon theexistingmajor historiesofthe American developments.While we cannot coverthe general developmentof quantumelectronics in theUSSR within thescope of oneshort article, it is possi- bletofocus on thekey local laboratorythatwas responsiblefor theinitial inven- tion of theSovietmaser andcompare itscharacteristicfeatureswiththe American analog. We will try to reveal thefactors,constraints,and opportunitiesthatwere at play in theSovietcontext andallowed Prokhorovand Basovtoachieve their

9 Forman 1987;Forman1992; Forman 1995;Forman1996. Forarecent review of Cold Warphys- ics, see: Oreskes2014. 10 Hacking1999, on 179. 11 Bromberg 1991,onXII. 12 Dunskaia 1974;Bertolotti2005; Hecht2005;Vakulenko 2006.For acomparisonbetween East andWestGermany,see:Albrecht2019.

378 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics breakthrough results. Ourgoalistodevelop an analysis capable of capturingand characterizing bothsimilaritiesand differencesand addressing thequestionof what happened when scientists formed in strikingly differentscientificand politi- calculturesbegan to asksimilar questionsand aimatsimilar goals. We will see that although Sovietand American scientists conceivedofthe same kind of device,theydid nothavethe same understandingofits functioning, duetotheir groundingindifferent academicculturesand research traditions. Thefirst sectionofthisarticle describesthe research tradition of theSchoolof Oscillations, ascientificschoolestablished in theUSSR before WorldWar II to whichProkhorov belonged andonwhose conceptual methodshereliedinhis work on themaser.Section 2addresses themilitarizationofSovietscience that startedinthe late1930s andextendedmuchfurther during theearly Cold War, itsimpactonthe careersofphysicistsofProkhorov’s andBasov’s generations,and theirresearchgoals.Section 3discusses howthe strategy of following theAmeri- canexample of building theatomicbomb, summarized in theSovietslogan“to catchupand to surpass,”alsoexpandedbeyondnuclear physicsand wasadopted by researchers in otherfields, includingProkhorov’s groupand itsfocus on micro- wave spectroscopy. Section4finallyarrives at theinvention of themaser,provid- ingacomparison of theSovietand American approaches to theinvention and theirrespectiveconceptualizationsofthe device.Inthe conclusion,wesummarize thesimilaritiesand differencesofthe American andSovietpaths to masers andre- flectonwhatlessons this comparativecasestudy offers to thegeneral conceptual problems of militarization andconvergence in Cold Warscience.

1. TheSchoolofOscillations Aftercompletinghis studiesofphysics at LeningradState University,inthe summer of 1939 AlexanderProkhorov became agraduatestudent (aspirant)at theLebedev InstituteofPhysics,alsoknown as FIAN,the Russianacronym for thePhysicalInstitute of theAcademy of Sciences.FIANhad recently transferred to Moscow,togetherwiththe headquarters of theUSSR AcademyofSciences, andwas developed by itsdirectorSergeiVavilov into amajor hubofSovietphys- ics. Many of itsleadingresearchers belonged to theso-called Mandelstam school, or School of Oscillations,formedaroundand underthe intellectual tutelage of theMoscow University professorLeonidIsaakovichMandelstam(1879–1944). Mandelstam andhis lifelongcollaborator NikolaiDmitrievich Papaleksidevel- oped an original approach to many fundamentalphysicalproblemsbased on the generalconcept of oscillations,especially nonlinear ones,thatunderlieawide rangeofnatural processesinvarious,otherwise unrelated, fieldsofphysics. Prokhorov, andlater Basov, both received theirprofessionaltraininginFIAN’s LaboratoryofOscillations, wheretheylearned thebasic methodology andcon- ceptualapproachesofthe Mandelstam school.13 Theorigins of theoscillatory approach to physicscan be tracedbacktothe work of theGermanphysicist KarlFerdinand Braun, oneofthe pioneers of radio andawinner of thephysics Nobel prizeof1909 forhis contributions to wireless

13 Pechenkin2019.

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telegraphy.Mandelstamand Papaleksistudied andcollaborated with Braunin Strasbourg andBerlinand acquiredtheir expertiseand earlyacademicrecognition in thefield of radiotechnology.TheybothreturnedtoRussiain1914, with the outbreak of WorldWar I, andcontinued theirresearchonradiotechnology there. Thewar,the Revolution,and theCivil Warinterrupted most of theexistingfor- eign contacts forRussian scientists.Mandelstamand Papaleksinow relied on the fundingand institutionalsupport from thedevelopingSovietindustryand also establishedanacademicbaseatMoscowState University,where Mandelstam helped trainanewgenerationofphysicists. Theirresearchprogramseventually diverged from thosefollowed by Braunand hispupilsinGermany in twofunda- mental aspects. Whilethe origin of many of hisideas andapproaches, andthe main thrust of hisefforts,remainedfocused on radiophysics,Mandelstamunder- stood that similarpowerfulmethods andthe common conceptual apparatusof themathematicaltheoryofoscillationscould also veryeffectively applytounre- solved problems in otherbranchesofphysics,including optics,electronics,acous- tics,mechanics,control devices,and thequanta. Many of hisstudentsexpanded into thesevariousresearchfields, andmoredifficult problems that they encoun- teredrequiredthe useofnonlinear oscillations,the mathematical method that helped establishthe Mandelstam school as amajor pioneerinthe emerging field of nonlinear physics.14 TheSchool of Oscillationsmadegreat stridesduringthe 1930sand expanded institutionally.By1936itincludedanetworkofsix importantresearchinstitu- tionsinthree cities:FIANand Moscow StateUniversityinMoscow; theLenin- grad Electro-Physical Institute(LEFI), theIndustrialInstitute andthe Central RadioLaboratoryinLeningrad;and theGorky StateUniversityinGorky.Man- delstamshunned administrativepositions andresponsibilitiesbut consultedand provided intellectual guidance to awidenetworkofscientists, engineers, andtech- niciansworking in academic institutions,applied research labs,and industrial set- tings, effectivelyensuringwhattheyregardedasa“unified research strategy.” The Sovietstate’s view of radioand relatedtechnologies as animportant priority for therapidlymodernizing country helped supportanumber of research programs of theMandelstamschool. Reflecting thehighprestige andresources grantedto thefield,radiophysics wasrecognizedasaseparateacademicdisciplineinthe Sovietuniversitysystemand curriculum.The School of Oscillations’research style didnot separate fundamentalscience from technology,but successfully de- velopednovel approaches in basic scienceinconjunctionwithmanypractical ap- plications andtechnological inventions, to thelikingofSovietofficials.15 Circa1930, nonlinearphenomena andmathematicalmethods becameamajor preoccupationfor many scientists in theSchool of Oscillations. Theinitial impe- tuscamefromthe analysis of some radiodevices butdeveloped into ageneral un- derstandingthatthe physical world wasessentiallynonlinear andrequiredanew, more sophisticatedand rigorous mathematical treatment.The major theoretical

14 Physical systemsare usuallyidealized so that they canbedescribed by linear equationswithrelative- ly simple solutions. Thenextlevel of complexity,for exampleevenasimple pendulum with oscilla- tionsthatare nottoo small, requires nonlineardifferentialequations. 15 Pechenkin2019.

380 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics breakthrough in that directioncamewiththe conceptofself-oscillation. Alexand- er A. Andronov (1901–1952),one of Mandelstam’sfirst students whoalsopos- sessed outstandingmathematicalskills,discoveredalargeclass of non-idealsys- tems—withresistanceorfriction, andalsowithapermanentsourceofenergy— forwhich theresulting behavior takesthe form of stable undamped oscillations with characteristic parameters determinedbyinnerfeaturesofthe system itself, rather than itsinitial conditions or externalforce. Andronov labeled such phe- nomena “self-oscillations,” understood them as essentiallynonlinear,and proceed- ed to develop asophisticated mathematical apparatuscapable of describing theirfrequentoccurrences in the real world. As acollectiveeffort, othermembers of theSchoolofOscillationsenrichedthatframework further, into what becameknown as thegeneral theory of nonlinearoscillations, andapplied it to solvechallengingproblems in diverse rangeoffields, includingradio physics, acoustics, mechanics, chemistry (periodicreactions), andbiology.Inthe wordsof AmyDahan Dalmedico, “Self-oscillations provided thebasis forAndronov’selab- orationofthe newparadigmofnonlinear physicsthatMandelstamhad called for.”16 By themid-1930s theschoolhad developed theanalysis forseveral paradigmat- ic examples of self-oscillating systemsthatweredescribed in textbooksand used forthe training of subsequent generationsofstudents. Thefirst such textbook, Theory of Oscillations,writtenbyAndronov, Semion Khaikin, andAlexander Vitt, waspublished in 1937.17 Amongthe self-oscillating systems that couldproduce undamped oscillations were musical instruments, pendulum clocks,and vacuum tubes.The firstfundamental question handledinthose studiesconcerned the transformation from apermanent,non-periodicsourceofenergy, forexample constant blowing, loweringofweights,orconstanttension from apower supply, into aperiodic, oscillatorybehavior by thesystem. Furtherquestions focusedon variousfactors that determinedand influenced thepropertiesofself-oscillations, theirformand frequency,and in particular thecharacteristics of thestationaryos- cillations,which occurwhenthe saturation effect takes place, namely when one of thesystem’sparameters reachesaphysical limit. In 1950 GabrielGorelik,one of Andronov’s collaboratorsinGorky,published anotherinfluential textbook, Os- cillationsand Waves, with additional paradigmatic examples andapplicationsof thetheoryofoscillations. Radio physicsstill remained themainareaofapplica- tion of itsbasic concepts,but furtherextensionsand elaborations of thetheoryin- cluded an ever widening rangeofdisciplines,fromnuclear physicstoastronomy, from biologytogeophysics, andcontrol devices.18

16 Pechenkin2002; Dalmedico2004, on 237. Unlike themorefamiliarforced oscillations caused by aperiodicexternal force, self-oscillationsare sustainedbyanon-periodic source of energy anddo notdependoninitial conditions. 17 Andronov andKhaikin 1937. Alexander Vitt wasarrestedin1937, during theStalinist purges,and hisnamedid notappearonthe titleofthe firstprinted edition. Acondensed Englishtranslation waspublished as part of theproject on nonlineardifferentialequations undercontractwiththe Office of NavalResearch, edited underthe directionofSolomon Lefschetz. See: Andronov and Khaikin1949. 18 Gorelik1950.

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Thetradition of theSchoolofOscillationsdemonstratesthatalready before WorldWar II,Sovietphysics developed andsustained some of theimportant fea- turesthathavemoreoften beenseenascharacteristicofthe postwarstyle of aca- demicphysics,including closeentanglementbetween fundamentaltheoryand thepractical developmentoftechnologicalgadgets,interdisciplinarity,and the abandonment,atleast in theactualpractice, of therestrictive ideology of pure sci- ence.19 We shallnow seethatthose featuresbecameimportant andnecessary,al- though notyet sufficient conditions forthe invention of themaser,the accountof whichrequiresseveral additional factorsassociatedwiththe militarization of phys- icsresearchafter WorldWar II.

2. Militarization andSecrecy During Prokhorov’sfirst years as agraduatestudent in FIAN’s Laboratory of Os- cillations,hetookpartinamajor studyonthe propagationofradio waves throughthe ionosphere usingaspecial rangefinderdesignedbyMandelstamand Papaleksi. Theirapparatus used radio-interferometry to measuredistances andthe velocity of propagationofradio wavesindifferent conditionswithhighaccura- cy.20 With thestart of thewar in 1941,Prokhorov interruptedhis doctoral studies andvolunteeredfor military service. Lieutenant Prokhorovservedinthe infantry division in whichheusedhis technicalskills in reconnaissance. Afterhavingbeen woundedtwice anddemobilized from thearmy, he returned to FIAN andre- sumedhis graduatestudies in 1944.21 Hisnew research assignment linked the theory of nonlinearoscillationswithone of themajor tasksofscience during WorldWar II—the development andapplication of radartechnologies.Prior to thewar,several of Mandelstam’s collaborators worked as consultants forthe mili- tary andin1934 demonstrated to Sovietmilitaryofficials thefeasibility of radio- location.Several poorly coordinatedresearchgroupsyielded promisingresults andtestedthe firstprototypesofradar forthe RedArmyasearly as 1939. The startofthe war,however,disrupted most of theseactivities. Awell-funded andco- ordinatedradar program was resumedbythe Sovietmilitaryonlyin1943, with allied help.22 By thetimeProkhorov returned to hisscientificworkatFIANin1944, radio- locationhad moveduptothe topofresearchprioritiesfor physicists. TheLabora- tory of Oscillationsdefined itsmainfocus as “extremely relevant presentquestions on generation,modulation, andapplication of super-high-frequency oscillations,” i.e.,microwavesusedinradiolocation. Itsresearchers busied themselves with de- veloping nonlinearmethods to createatheory suitable formicrowave frequen- cies.23 Prokhorov’sdissertation, accordingly, dealtwiththe problemoffrequency

19 Forman 1995;Leslie1993. 20 Thesemethods helped Soviet mathematical physicists BorisVvedensky,VladimirFock, and MikhailLeontovich(thelatterastudentofMandelstam) developand improve thetheoryofprop- agationofradio waves. See: Wait 1959. 21 Prokhorov1996. 22 Erickson 1972;Kobzarev2007. 23 Prospective plan for1944onthe theory of oscillations andradio-physics by Sergei Vavilov, Archives of theRussian Academy of Science (ARAS),532-1-90,l.10.

382 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics stabilizationoftubegenerators. He obtainedhis degree of CandidateofSciences (kandidatnauk,roughlythe equivalentofaPh.D.) in 1946. That work,which Prokhorovconducted underthe supervisionofSergei Rytov, canillustratehow thetheoryofnonlinear oscillation handledrealdevices and practical problems.Althoughnot directly part of amilitaryradarproject,the lab- oratoryworkedongeneral theoreticaltasks relatedtothatoverall goal. As Rytov laterrecalled, “The appeal of theworkonstabilization of frequency wasnot acci- dental,but dictated by the‘social needs’ of that time.Radiolocation, radiocom- munication, television:theyall demanded generators with more andmorestable frequencies.”24 Rytovhad improved thesmall parameter perturbation method to make it applicable to studyfrequency stabilizationand guided Prokhorov’sand anothergraduatestudent,MarkE.Zhabotinskii’s, work on thestability of atube generatorwithquartzstabilizer.25 Theirtheoretical treatmentpredicted original phenomenathatwerelater verified experimentally,suchasthe existence of islands of stabilityamidmismatching intervalsinsomespecificconditions. In aseparate paperaddressed to engineers, Zhabotinskii provided an intuitive pictureofthe stabilizationprocess andasummarywithcalculatedformulasfor stable frequen- cies that couldbeusedtoproduce more stable generators of microwaves.26 Thethreecollaborators,Rytov,Prokhorov,and Zhabotinskii,received the 1947 Prizefor best work in radiophysics,named aftertheir late teacher, Mandel- stam,who haddiedin1944.27 Theirresearchwas conductedinthe spirit of the School of Oscillations andinaccordancewithits characteristic approaches.Start- ingfromsophisticated mathematical methods, it proceededtoconcreteapplica- tionstowardssolving an importantpractical problem, withresults expressed in engineeringlanguageand materialized in workable devices. Thesamepattern characterizedmanyother research programsdeveloped by Mandelstam,Andro- nov, andtheir collaboratorsand reflected generalexpectationsplaceduponSoviet physicists.The generalprospective plan fortheir institute, FIAN,developed by Vavilov in 1944,displayed thetypical Soviettendencytodefinethe value of asci- entificproject in termsofits possible future applications,ratherthanits contribu- tionstopureknowledgeassuch. Paul Forman identified asomewhatsimilar ten- dencyinpostwar American physics, namely the“gadgeteering,” that steeredphys- icists’researchgoals towardsthe developmentofdevices such as atomic clocks and, eventually,the maserand thelaser.28 In both countries, postwarimprovementsand developments in radartechnolo- gy demanded newmethodsofgeneratingradio waveswithevershorter wave- lengths, from thecentimeter into the millimeterregion, wherethe existingtech- nology of generators based on vacuum tubescametoits technicallimit.Joan Bromberg describedthe demand fornew reliable sourcesofmicrowavesas coming from twosides.The military wanted more compactsources of millime- ter-waves forreducingthe weightofguidedmissilesand radars,and forgreater se-

24 As quoted in Prokhorova 2006,on48–49. 25 ARAS,532-1-122,l.1–10. 26 Rytovetal. 1945;Zhabotinskii1946. 27 Rytovetal. 1948. 28 Seenote23(Prospectiveplanfor 1944…);Forman1996.

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crecyinshort-range communications.Anewsubdiscipline in physics, microwave spectroscopy andits growingcohortofresearchers,utilizeddecommissioneddevi- cesfromthe wartimeradar project andapplied them to thestudy of atomic and molecularspectra in previously unexplored wavelengthscirca andbelow 10 cm. Formanyimportant molecules, theabsorptionspectra layinthe millimeter range andrequiredcorresponding sources of radiation.29 In 1948 Prokhorov startedanew, independentresearchprojectthateventually formed thebasis of hissecond, more advanceddissertationfor thedegreeof Doctor of Sciences (Doktor Nauk), whichheobtainedin1951. This time he movedbeyondthe core focusonradio physics, butfollowedthe School of Oscil- lations’ interdisciplinaryagendabybringingits methods andapproachesto aneighboring laboratory in FIAN that worked on nuclearphysics.Aspartofthe Sovietatomicbombeffort, FIAN builtanaccelerator of particles, thesynchro- tron, anduseditfor thestudy of nuclear reactions. In 1944 Dmitry Ivanenko andIsaak Pomeranchukpredicted what eventually cametobecalledthe “synchro- tron radiation,”which determined thelimitsofpossible energy acquired by accel- eratingparticles.For nuclearphysicists, theeffectpresented amajor difficulty for furtherimprovementsinacceleratingpower of thesynchrotron,but Prokhorov wanted to investigateits potentialusefulapplication as apossiblenew source of microwaveradiation.30 This time he startedsupervising hisown studentswho formed thecoreofhis future research group. Sincethe fall of 1948 he washelped by Basov, asecond-year studentofthe Moscow Mechanical Institutewho joined thelaboratoryasanengineering assistant. Thefollowing year Prokhorov’sgroup acquired theirown accelerator, abetatron. With thedevicecameits handler, AlexanderI.Barchukov,astudentofthe Bauman Moscow StateTechnical Uni- versitywho was alreadyfamiliarwiththe acceleratortechnology.31 Workingatthe intersection of atomic andradio physics, Prokhorovstudied ex- perimentally thepropertiesofthe synchrotronradiation.While importantfor the functioningofthe acceleratoritself, then oneofthe newest technologiesinhigh- energy physics, theresults couldalsoprovide apractical device,anewkindof generatorofmicrowaves, or so,atleast,was Prokhorov’shope.32 Accordingtohis analysis,the powerofnon-coherentradiation emittedbyelectronbeams in the synchrotronwas proportional to thenumberofelectrons,N,while thepower of coherent radiation, duetoelectrons moving in bunches, couldbeproportionalto N2 forelectronbeams with ahighdegreeofbunching. Electronscirculatedinside thesynchrotron with afrequency equaltothatofthe high-frequency external fieldusedtoacceleratethem. Thesynchrotron radiationincludedmanyhigher

29 Bromberg 1991,on13–14. 30 FIAN physicists also worked on anotherpossiblestrategyfor generating shortmicrowavesbased on theCherenkov (orVavilov-Cherenkov)radiation,which they haddiscoveredinthe 1930s. See: “Cherenkov,Pavel Alekseevich”2008. In theUnitedStates, Townes also explored thestrategyof usingthe Cherenkoveffectfor microwavegeneration. See: Forman 1992. 31 Prokhorova 2006. 32 Basovlaterrecalled: “In ourinvestigations, we aimedatthe creation of such radiationsources that wouldcontinuouslycover awiderange of centimeter waves.”See:N.G.Basov,interviewby Arthur Guenther, 14 September1984, NielsBohrLibrary &Archives,AmericanInstitute of Phys- ics(AIP),College Park,MDUSA,http://www.aip.org/history-programs/niels-bohr-library/oral- histories/4495 (lastaccessed27November2019).

384 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics harmonics, permitting thegenerationofmuchshorter waves. In Prokhorov’sin- vestigation, thefrequency that corresponded to the16thand 24thharmonics gen- erated 3cmand 2cmwavelength, correspondingly,withthe achieved power 6 output of about10À W. He estimatedthatthe synchrotroncould be used as agenerator of microwaves rangingfrom1mm to 0.1mmwithpower output be- 6 4 tween10À Wand 10À W, “considerablevalues[then]hardlyachievablebyother methods,”heconcluded.33 Though useful forthe analysis of accelerators andtheir radiation, theresults ul- timately proved somewhatdisappointing:the synchrotronradiation wasstill too weak andincoherentfor apractical generator of microwaves.Eventually,the syn- chrotron wouldnot be able to competewithother,morepowerfulgeneratorsin thecentimeter-waveregion. Basedonhis estimatesfor millimeter waves, Prokhor- ov stillexpressed ahopethatwithasignificantincreaseinthe number of acceler- atingparticles,the synchrotroncould be used as asourceofshortwave radiation forthe needsofspectroscopic research.34 In 1951 thefield of microwavespectros- copy wasstill an Americanspecialty,practically nonexistentinthe USSR,where wartimemilitaryradar equipmentwas notyet made accessible to academic re- searchers. ButProkhorov’s synchrotronradiation projectwas classified,not so much becauseofits direct interesttothe military,but becauseofits association with theparticleaccelerator,adevice initiallybuilt as partofthe Soviet atomic bombproject.The resultsofhisresearchwerepublished only in 1956, when it becamesufficientlyclear that they wouldnot lead to anew powerful generatorof microwaveradiation.Safelydeclassified, they werestill original andrelevant enough as astudy of thesynchrotron radiationtowarrant publicationinanaca- demicjournal.35 Thetwo American physicists whoconceived of theprinciple of themaser, Townes andJosephWeber,had also beeninvolved with thedevelopment of radar technologyduringand afterthe war. Thehistoricalconnectionbetween themaser andmilitary-relatedradar research,and with theclassifiedquest fornew schemes of generating microwaves,isanestablishedand well-studiedphenomenoninthe American case,but hasnot been previously discussedaspartofthe Sovietpathto- wardsthe maser.36 It is possible to conclude nowthat, similar to theirAmerican colleagues,Prokhorov andhis firststudentsalsotookpartinthe classified search fornew technologiestogeneratemicrowaves,withaview towardstheir possible applications in military radiolocation. In theirlater comments on thedevelop- ment of theirresearchonmasersand lasers, theSovietphysicists, just like their American counterparts,did notwanttoacknowledge this military connection. Such denial relied,inpart, on standard secrecyrestrictions, andinpartonthe fact that after1955, military-relatedclassifiedresearchwas losing itsmantleofprestige in theeyesofmanySovietscientistsand thescience-interestedpublic, whowere increasingly looking at international-oriented,basic researchasamore prestigious

33 Tr anscript of thedefense session. ARAS,532-1-194.l.15–16. 34 ARAS,532-1-194. 35 Prokhorov1956. 36 On thecrucialimportanceofthe radarproject as asourceofbothexpertise andhardwarefor the subsequent developmentofquantum electronics, see: Bromberg 1991;Forman1995.

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andrespected occupation foracademicscientists. In lateraccounts, Prokhorov andhis collaborators preferredtodescribetheir invention of themaser as originat- ingfromfundamental scientific concerns with thedevelopment of microwave spectroscopy.37 Whilepresent in both cases, thedegreeofmilitary involvementwas notthe same,however.Inthe US,Towneshad been much more explicitly andcentrally involved with military projects, as researcher,consultant, andmanager of classi- fied work.Bycomparison, Prokhorov andBasov werefull-time employeesinan academic researchinstitute,FIAN, whichhad ashare of itsfunding coming from military projectsand apartofits research conductedinsecrecy,but stillprimarily focusedonopenlypublished investigationsinphysics evenduringthe most mili- tarizedperiod, 1947 to 1953. Still, eveniftheir part-timeinvolvement in classi- fied researchwas only potentially relatedtopossiblemilitaryapplications, such an awareness must have been presentintheir minds, at leastrhetorically.Among Prokhorov’sfirst publicationswas ashort postwarpaper in thepopular science magazine NaukaiZhizn (Science andLife) andaseparately published booklet ex- plaining to layaudiences thefundamentalsofmilitary radiolocation. Thetexts reveal hisfamiliaritywithradar physicsand an understandingofthe importance of hisworkonfrequency stabilizationand newschemes forthe generation of shortmicrowavesfor radartechnology. 38 Prokhorov’sclassifiedworkonthe synchrotronradiation coincided with the last yearsofStalin’srule, theperiodofutmostsecrecy,Cold Warparanoia, and spymania in theSovietUnion.While many Soviet scientists privatelyand grudg- ingly disapprovedofthe excessivesecrecy,manyothers, especially in theProkhor- ov generation, whorosetoprofessionalmaturitybetween 1940 andthe mid- 1950s,consideredclassifiedworkonmilitarytasks highly important, prestigious, andrewarding.The values of theSoviet frontovik (war veteran) generationwere formed underthe decisive influenceofthe GreatPatriotic Warand continuedto generate that ethosalsothrough theearly Cold Waryears.Asecretaryofthe Komsomol organization at theLeningrad Electro-TechnicalInstitute captured the mood of many of Prokhorov’scontemporarieswhenheaffirmedinaninterview that people of histimewere“deeply influenced by thespiritofthe frontovikgen- eration,”characterizedbywar-related virtuessuchasheroicpatriotism, loyalty, collectivism,and self-sacrifice, whichdominated thelandscape of theInstitute untilthe mid-1950s.39 Both Prokhorovand Basov became membersofthe Com- munist Partyinthe early1950s and laterperformed leadingroles in defense-relat-

37 Forexample,N.G.Basov in hisoralhistory interview(seenote32) denied anylinkwithmilitary investigations.Suchdenials were more typicalofthe 1980sratherthanthe 1950s. In 1984 Soviet physicists were publicly opposing Reagan’s StrategicDefense Initiative.Inaninterview recorded on thesameday as Basov’s, Prokhorovvoicedhis opposition to military applications of lasers:“Iwish that thedream of ah…the warbylasers,Ithinkso, it’srathersilly thing, andthat oneway in whichwemustnot go.” Prokhorov, Aleksandr, interview by Arthur Guenther, 14 September1984, NielsBohrLibrary&Archives,AIP,College Park,MDUSA,http://www.aip.org/history-pro- grams/niels-bohr-library/oral-histories/5048(last accessed 27 November 2019). 38 Prokhorov1946;Prokhorov 1948. 39 Fürst2006, on 224–225.

386 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics ed research in theSovietUnion. Both remained supporters of thesocialist system to theend of theSovietUnion.40 Many physicists of that generation accepted as normal andjustified themobili- zation of scienceand scientists fordefense-related projects, worked in mission-ori- entedinstitutions, ofteninrelativeisolation,under conditions of utmost secrecy andsurveillance, withoutpermissiontopublish openly theirmostimportant re- sultsand receivepubliccreditfor them.Thisespecially appliedtoscientistswho were involved in theatomicbombresearch, such as Igor Kurchatov, whosaw his scientific responsibility forthatproject as adirectcontinuationofthe wartime effort,requiring comparable disciplineand self-sacrifice.41 Thus, secrecyand com- partmentalization, the essential elements of the historyofthe maser in the United States, were also strongly present on the otherside of theIron Curtain. Growing fromthe entanglementbetween physicsand militaryresearch during andimmedi- ately after World WarII, this similarity extended over mattersoforganization, pro- fessional ethos, andmanagement of major projects in science. It also affected,aswe shallsee in thenext section, matters of intellectualcontent, ideas, and inventions.

3. Catching up andSurpassing:fromMicrowave Spectroscopy to the Maser AfterProkhorov defended hisdissertationand moved up theacademicladder from agraduatestudent to asenior research associateatFIAN, hislivingcondi- tionsbegan to improvedramatically.Not only didhis salary rise significantly, but he also acquired other, no less importantprivilegesofSovietsociety,suchasaccess to stores with betterquality food andgoods, andasmall plot of land foradacha outside Moscow.For awhile,however,hestill hadtoliveinacrowded15.5m2 room whichhesharedwithhis wife,son,and mother-in-law, andwithone table used forbothworkand eating.Insummers he couldhavealittle more privacy with an improvised writingdeskmadeofapiece of plywood nailed to acornerof hisbalcony. Hislivingconditionsimprovedin1950 when thefamilymoved to anew apartmentofthree roomsinacondominiumbuilt specially forFIAN’s workers, located near thenew building of hisinstitute.42 Prokhorov’s newliving standard reflectednot only hisacademicdegreeand position,but thegeneral priv- ileged status of scienceinthe postwar SovietUnion.Those privileges camewith stringsattached. In exchange fortheir improved fundingand prestige,Stalinex- pected Sovietscientists“notonlytoovertakebut also…to surpassthe achieve- mentsofscience outside theboundariesof[their] country.”43 Although hispri-

40 In the1980s,Prokhorov andBasov advisedthe Soviet government on military scienceand security. “Theiropinion wasconsideredtobeveryimportant.The leadersagreedtowhattheysaid,evenif they didn’t understand what they said.” See: Hey2006, on 41.For theAmericansideofthe story, see: Wilson 2015.Prokhorov also signed an official letter attackingthe dissidentAndreiSakharov forthe viewsonnuclear deterrentpublished in ForeignAffairs. See: Dorodnitsynetal. 1983. 41 Kojevnikov 1999,on241. 42 Prokhorova 2006. 43 “SpeechDelivered by Stalin at aMeeting of Voters of theStalinElectoral District,Moscow,”9Feb- ruary1946, Historyand Public PolicyProgram DigitalArchive (Gospolitizdat,Moscow, 1946), https://digitalarchive.wilsoncenter.org/document/116179 (lastaccessed27November2019).

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mary audience were scientists workingonthe Sovietatomicproject,Stalin’smes- sage,and theassociatedprivileges, didnot remain restrictedtonuclear physics, butextendedtoother scholarlyfieldsaswell. Sovietphysicists, in particular,were expected to competewithAmericans across theentirespectrumofadvancedaca- demicfields, old andnew.44 Onesuchnovel field, microwavespectroscopy, emergedinsomeAmerican lab- oratories just beforethe endofthe war,but boomed especially during theearly postwar years, when many physicists returned to theiruniversitiesarmed with ex- pertiseand hardware byproductsofthe wartimeradar project. AccordingtoPaul Forman,microwavespectroscopybecamethe “premier exampleofaflourishing fieldofphysicalresearchcreated—inevery sense—by radar.”45 Theresults of its investigationsalsoinfluencedsignificantly otherprestigiousdirectionsofresearch in atomic andnuclear physics. Thenew,muchmoreaccuratemeasurementsof theabsorptionspectra of atomsand moleculesenabled importantconceptualad- vances in quantumelectrodynamics andforcedtheoreticians to reformulatetheo- reticalmodelsofnuclear physicstofit thenew experimental data.46 With thedefense of his DoktorNauk dissertation in 1951 (the second academic titleinthe Soviet system,comparable to theGerman Habilitation), Prokhorov becameanaccomplishedresearcherready to lead hisown fieldofinvestigations andalaboratoryinthe institute. Following asuggestion by Sergei Vavilov, he chosemicrowave spectroscopyasabranch of sciencethatwas notyet developed in theUSSR,but wasrapidlyadvancing in theUS.47 Most spectroscopicresearch wasunclassifiedand openly publishedinacademicjournals, butincompliance with common patterns of thetime, it wasstill useful,for thepurpose of connec- tionsaswellasfunding,tohaveatleastpartofthe research activities associated with some secret military-relatedproject.According to archival reportsthatsum- marizedthe work of Prokhorov’slaboratorystartingin1952, aboutathirdofits research was classified andaimed at precise “determination of nuclearmoments, as orderedbythe decision of theUSSR Council of Ministers.”48 This aspect of hisworkwas obviously,evenifmarginally, relatedtothe atomic bomb project.In particular,precise measurementsofnuclear moments weresupposedtohelptheo- reticiansimprove thenuclear shellmodel,which struggledtohaveits numerical calculations conformtoavailableexperimentaldata.49 Prokhorov’smovetoanew directionofresearchthusappears to have beenmotivated by thegeneral stimulus to catchupwithWestern physicsinanovelfield that was also relevant forpresti- giousand militarily importantnuclear physics. Hisgroup’sfirst challengewas to build aspectroscope with high sensitivityand resolution, similar to those “described in generaltermsinthe foreign literature.”50 In the meantime, they mastered the new field theoretically and suggested solutions

44 Kojevnikov 2004;Kojevnikov2011. 45 Forman 1995,on422. 46 Schweber 2014. 47 InterviewofAleksandr Prokhorov(seenote37). 48 Laboratory report of 1955,ARAS, 532-1-251. l. 83-39. 49 Recentlypublished archival report:Basov 1997a; andBasov’s 1953 dissertation publishedinthe same volume,51–123. 50 Basov 1997b, on 17.

388 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics and possibleimprovements that, in their ownestimate, matched the level offoreign research in theoretical quality,while lagging behind in hardware. Their microwave equipment, as in the Americancase,camefrom radardevices thatwerestill manu- factured by the Soviet industrybut no longer neededbythe military. Initially,they acquiredareflex klystron that produced radiationofwavelengths between 5cm and 2.6cm. By usingits secondharmonic, theycouldgeneratewaves twice as short, but at reduced power andsensitivity ofthe spectroscope, which still didnot allowthem to study molecularabsorption spectrabelow1.3 cm.51 By comparison, transmitters of the k-bandradarswidely available to US physicists after the war could generate radiation of wavelength 1.25 cm with enough power to be employed in radars,muchmore thanwhataspectroscope required.52 Prokhorov’snextproblem,commonfor allspectroscopists,concerned the limits on spectral resolution.Inagasofmolecules,someare randomly moving to- wardsthe incoming radiation, whileothersawayfromit, whichaffects thefre- quency of theabsorbedradiationdue to theDoppler effect.The resultingDop- pler broadening of thespectrallines registered by thedetectorcan preventthe identification of twoseparatelines,iftheir frequenciesare close. Apossiblesolu- tion wasalready discussedinthe literature,following theproposalbythe Prince- tonUniversityphysicistsGeorgeNewelland RobertDicke to replaceagas of ran- domlymovingmoleculeswithabeam, in whichall moleculesmoveinthe same direction. By 1952, several teamsofAmericanresearchers were alreadyconstruct- ingoroperating microwavespectroscopes with molecular-beam absorption.53 Thetechnologyofmolecularbeams hadbeeninuse in physicssince thelate 1930s,thoughfor somewhat different purposes.One of theleading teams, Isidor IsaacRabi’sgroup at Columbia University,employedtheminamethod to deter- mine magneticmoments of atomic nuclei,under thenameof“molecularbeam magneticresonance spectroscopy.”54 In themid-1940s,Rabi’s collaborator Harold Hughes proposed afurther extensionofthe method to studymolecules with largedipolemoments.Electricresonance spectroscopywas analogoustothe magneticresonance method,but used anon-uniform electric field, insteadof amagneticfield,tomanipulatethe molecularbeam.55 In theresonance method, theabsorptionwas measured by thechangeinintensity of themolecular beam rather than by thechangeinintensity of theradiation,aswas more traditionalfor spectroscopy. Upon reviewing the literature, Basovand Prokhorovopted to construct their ownversionofamicrowave spectroscope that combined different existingideas in anew pattern. They planned to replace the gaswith amolecular beam in order to decreasethe Doppler broadening, to rely on Hughes’electric method to createand manipulate the molecular beam, buttomeasure the absorption bythe outbound radiation, ratherthan by the intensityofthe beam, as in theresonancemethod. Ac- cording to theircalculations, theyexpected suchacombination of the molecular

51 Laboratory report of 1955 (see note 48); Basov1997b;Kojevnikovand Mokrova2003, on 117. 52 Bromberg 1991,on13. 53 Newell andDicke 1951;Forman1992. 54 Forthe history of themolecular beam method andRabi’sgroup,see:Goldstein 1992;Forman 1995,on404–407. 55 Hughes 1947.

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beam resonance method with microwavespectroscopy to decreasethe broadening of spectrallines from 60 kHz, typical forgases, to approximately8kHz.56 They firstpresented theirproposalfor building amolecular-beam spectroscope on 22–23January 1953, at aclassifiedconferenceonmagneticmoments of nuclei.According to theproceedings,their calculations included an additional original idea:using thenon-uniform electromagneticfield to separate themole- culesinthe beambytheir quantumenergies. Atypical molecularbeamleavesthe oven as amixture of molecules,someinthe ground stateand some in excited, higher-energystates. Thedifferencebetweenthe numbersofmolecules in these states,which is usually afractionofapercent, determines therateofquantum ab- sorption.Ifone canseparateand only putintothe cavitythose moleculesthatare in thegroundstate,the spectroscope’s sensitivitycan increase by up to athousand times. Basovand Prokhorovpossiblyarrived at this idea as atrick to compensate forthe lowpower of theirmicrowave radiationsource.57 Theideaofseparationopenedupyet another, previously undiscussedopportu- nity.Oncethe moleculeswereseparated,explained Basovand Prokhorov, anew spectroscopicmethodwas at hand,namelytostudy emission spectrainstead of absorption spectra.For this,one hadtosendthrough thecavitythose molecules that were in an excited, higher energy state. Theirflight time throughthe cavity wastypically much shorterthanthe time needed forspontaneous emission,but theincomingradiation couldstill causeinduced emission.“Theobservedradia- tion will be, of course,induced,” wrotethe authors, concluding that “ifthe cavity hasagood enough qualityfactor…theprobability of emission of molecular energy approaches one. Allthe moleculespassing throughthe cavity irradiate.”58 In theirJanuary 1953 presentation,Basov andProkhorov didnot yetmention thecapacityofsuchadevice to generate or amplifyradiation;theytalked aboutit only as aspectroscope. Thepossibility that “Using amolecular beam in whichthe moleculesinthe lowerstate of thetransitionunder studyare absent, we canmake amolecular generator,”was firstdiscussed by them by theend of theyearinan extended,improved versionoftheir conference presentation,the papersubmitted forpublication in January1954.The last pagesofthatpaper discussedthe work- ingprinciplesand estimatedparametersofsuch adevice: Thesortedout molecularbeam, in whichmolecules in thelower stateofthe transi- tion understudy areabsent, is passingthrough acavity. During theflightinside the cavity,partofthe moleculesundergoes transitionsfromthe uppertothe lowerstate, impartingtheir energy to thecavity. If intracavitylossesare smallerthanthe emission powerofmolecules, self-excitation takesplace andthe radiationpower in thecavity increasesuptothe valuedeterminedbythe saturation effect.59

56 Paperpresented at themeeting on themagneticmoments of nuclei,January 22-23, 1953,ARAS 1522-1-59. l. 36-47. Thepaper waslater reprinted as Basovand Prokhorov1997a. 57 They estimatedthatmoleculeseparationcould increase thespectroscopesensitivity athousand times: Basovand Prokhorov1997a,on40–41.According to Basov1997a,the lowpower of their microwavesourcelimited thesensitivity of thespectroscope. 58 Basovand Prokhorov1997a,on41. 59 Basovand Prokhorov1954, on 437, emphasis added. Thesubmission date is 19 January 1954. However, accordingtosomeaccounts, thepaper wasinitiallysubmittedinDecemberof1953, but theneedfor asmall numericalcorrectioncausedits resubmission onemonth later. Thepaper was publishedinOctoberof1954. See: Karlov et al.2010, on 34.

390 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics

Basovand Prokhorov’sunderstanding of themaser principlereferredtothe conditionofself-excitation andthe energy of thestationary stateofthe oscillator determined by thesaturationeffect. It wasbased upon theconcept of self-oscilla- tion as developed by theSovietschoolofoscillationsand provided yetanother ex- ampleofaself-oscillating system.60 Theirpathtowardsthe inventionofthe maser, as revealed by thedocuments,can be summarized in thefollowingsteps. They puttogether, first, theproposalbyNewell andDicke to eliminatethe Dop- pler broadening by replacingagaswithamolecular beam; second,the method of manipulating molecularbeamsbynon-homogeneous electric fields developed by Hughes;and third, theconceptualapparatus of theSoviettheoryofoscillations whichpermitted them to envisage that underspecificconditions, stimulated radi- ationwould buildupinsidethe cavity andallowthe device to amplifyand to gen- erateradiation.Weare nowinabetterpositiontocompare the differencesand thesimilaritiesbetween theSovietand theAmericanconceptualizationsofthe maser.

4. ComparativeApproach: Experiment andTheoryinthe Inventionof theMaser In thecourseof1953, theSovietand theAmericanworktowards themaser were on converging paths. Townes conceivedhis initialideaofamicrowavegenerator based on stimulated emission in thespringof1951, andin1952,under hissu- pervision, hisPh.D. studentJames Gordon andpostdoctoralfellowHerbert Zeiger startedputting togetherexperimentalpiecesofthe possible device.In 1953 theyadjustedthe projectasaimingatamicrowavespectroscopeand ampli- fier,justtobesurethatevenifthe generatordid notwork, Gordon wouldstill have an accomplishment to defend hisdissertation.61 Basovand Prokhorov movedinthe opposite order: in 1952, they startedworking towards amicrowave spectrometer,beforeeventually shifting towardsanamplifier andagenerator.At thetime, neithersidewas awareofthe other’sproject. Archival recordsindicatethatBasov andProkhorov learnedabout Townes’s project in thesecondhalfof1954, afterthe Physical Review issuewith ashort paperbyGordon, Zeiger,and Townes reached theUSSR.Inthatlettertothe editor,the authorsdescribedingeneral termsthe workingprinciple of the“molec- ular microwaveoscillator” andannounced itssuccessfuloperation as ahigh-reso- lution microwavespectroscope.62 TheSoviets then hurrieduptopublish their owndetailed“Theory of theMolecularGenerator andMolecularPower Amplifi- er”inthe Proceedingsofthe USSRAcademy of Sciences.63 That they took almost

60 Thesaturation effect occurs when aparameter of thesystem, here theradiation power, reachesits physical limit. This is anonlinear effect.See:Gorelik 1950. 61 Forman 1992;laboratory report of 1955 (see note 48). 62 Gordon et al.1954. Earlierprogressreports appeared in the QuarterlyReportofthe Columbia Radia- tion Laboratory,aninternal publicationthatwas availableinColumbia University’sLibrary.There is no indication that theSovietteamwas awareofthese reportsand of Townes’project priortothe publicationinthe Physical Review. Starting with thesecondhalfof1954, thedocuments by Basov andProkhorov systematically included references to Townes’work. 63 Basovand Prokhorov1955a.

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twoyears to submit that paper, whichconceptually was notfar beyondthe paper deliveredinJanuary 1953, indicatesthattheyhad notbeenaware of theworkof Townes’s team.WithanEnglish version of thepaper in hand,inearly April1955 ProkhorovflewtoEngland,where he metTownesfor thefirst time anddiscussed theirapproaches to thenew device face-to-face.64 By comparingthe earlypapers andlecturenotes by theSovietand theAmericanteams,wecan analyzehow their respective scientific cultures influenced theirdifferent understandings of the maser. In thefirst official presentationspecifically devotedtothe moleculargenerator, at themeeting of theAll-Union SocietyofRadiotechnologyand Radiocommuni- cation in October1954,Basov andProkhorov definedthe device as a“self-oscil- lating system that uses theenergyassociatedwithtransitions betweendifferent molecularlevels.”65 Theirearly explanations andcalculationsofthe newdevice’s operationwereusually basedonananalogywiththe vacuum-tubegenerator,the paradigmatic,well-studiedexample forthe theory of self-oscillations. Thecavity andthe electromagneticradiation inside it played rolessimilar to thecircuit and theelectricchargefor thevacuumtube. Many of theterms andconceptsusedin theanalysiswerefamiliartoradio engineers. Prokhorovwould laterexplain the analogy in hisNobellecture: As is well-known from radioengineering,any system able to amplifycan be made to oscillate. Forthispurpose,afeedback coupling is necessary. Atheory forordinary tube oscillatorsiswelldeveloped in theradio range…Thereforethe conditionof self-excitationfor thequantum oscillator [maser or laser] should be writteninasimi- larway as foratube oscillator.66 As with otherself-oscillatingdevices,their theory of themaser was basedfrom theoutsetonanonlineardifferentialequation. That definition dictated thesys- tem’scharacteristics to be observed (namely, thecondition of self-excitationofthe stationary state),the main questionstoask (What qualityfactorQwasnecessary forself-excitation to happen?Whatare thefeaturesofthe stationary state?), and howtoanswerthem. Themaser differed from thepreviouslystudied self-oscillat- ingsystems by itsspecificsourceofenergy, whichwas quantumratherthanclassi- cal. That part of thesystem, thebeamcontainingalargeensembleofquantum oscillators(molecules),had to be describedwiththe help of quantumstatistics. Theresulting semiclassicaltheorycombinedaquantumapproachfor molecular transitionsand aclassical,but nonlinear theory forthe descriptionofthe cavity radiation. Overall, theSovietpathtowards themaser canbecharacterized as theory- driven.Their commandofarelatively advancedtheoryallowed Basovand Pro- khorov to calculate, envision andpredict certaincharacteristics of thesystem, whilethe actual building of thedevicelaggedbehinddue to thelackofsufficient- ly advancedhardware. As an example, in oneofthe firstpaperstheycalculated

64 Basovand Prokhorov1955b. 65 Basovand Prokhorov1997b,on127. 66 Prokhorov, Alexander, “Nobel Lecture: QuantumElectronics,1964,”110 –16, on 112–113: http://www.nobelprize.org/nobel_prizes/physics/laureates/1964/prokhorov-lecture.html (lastac- cessed 27 November 2019). “Mandelstam’stypical wayofspeaking,”acommentonthispassage in Pechenkin2002, on 291.

392 Ber. Wissenschaftsgesch. 42 (2019):375 –399 Convergence in ColdWar Physics theminimum qualityfactorQand themaximum powerfor amolecular genera- torbased on quantumtransitions in cesium fluoride CsF, whichwould generate 3.7cmwaves.Havingconcluded that thestate-of-the-arttechnology couldnot produceacavity with Qsufficienttoachieve theself-oscillationregime, they argued that it wouldbenecessary to usemolecular beams with higher than usual density. Forthe usualmolecular beams,theypredicted,the device couldstill be useful as an amplifierand spectroscope of very high resolution andverylow noise, butnot as aquantum generator.67 Guided by similarcalculations, from 1954on, Basov ledthe work on technicalimprovements of theirapparatus,focus- ingespecially on thequality of thecavityand thefocuser that sorted themole- cules, in ordertoincreasethe densityofthe molecularbeamand eventually ach- ieve thegenerationregime.68 Accordingtothe initialannouncementbyGordon, Zeiger, andTownes, “[a]n experimental device,which canbeusedasaveryhigh-resolution microwavespec- trometer,microwave amplifier, or averystableoscillator, hasbeenbuilt andoper- ated.” This formulationconveys theabsence of thegeneral conceptofself-oscillat- ingsystems.Theyrefer to themaser simply as an “experimentaldevice” defined by itsfunctions—whatitcould do—ratherthanits generaltype. Corresponding- ly,Gordondescribed themaser in mostly operationalist terms, presenting the block diagramofthe apparatus, itsmainparts andthe workingprinciple,and the conditions in whichitcould function as an oscillator,anamplifier,orspectrome- ter. He discussedthe power,stability of oscillation, noisefigure, andresolution (spectrallinewidth)asexperimentally measurable, rather than calculated,charac- teristics. Hisonlycalculation concernedthe spectral linewidth, whichtheyesti- matedat4kHz, of thesameorder of magnitudeasthe observedvalue of 6–8kHz.Fromthe useofthe device as spectrometer,theyalsoreportedexperi- mental measurementofthe hyperfinestructure of ammoniainversion transi- tions.69 Citing theAmericanannouncementofthe maserintheir October1954pre- sentation, Basov andProkhorov mentionedcriticallythat“no theoreticalconsid- erationisgiven,and theestimateofthe linewidthshows that theauthors do not understand wellenoughthe workingprinciple of themoleculargenerator.”70 Ac- cordingtoBasov’s analysis,the spectral linewidthcan either be determined by the time of flight of themolecules throughthe cavityorbythe lifetime of theirexcit- ed state. In thestationaryregime, when theradiationfield inside thecavityisin- tense, thelifetimeofthe moleculesisshorter than thetimeofflight, in whichcase thesaturationeffectdeterminesthe spectral linewidth. Gordon’s calculated value of thelinewidth at 4kHz depended on thetimeofflight. Taking into account thesaturationeffect, or nonlinearity, Basovobtainedanestimateof7kHz, in complete agreement with theobserved values. Later, in response to theSoviet theory of themaser,Gordon, Zeiger,and Townes publishedtheir owndetailed calculationbased on thelinear, first-order perturbation theory.Theyacknowl-

67 Basovand Prokhorov1954. 68 Laboratory report of 1955 (see note 48). 69 Gordon et al.1954. 70 Basovand Prokhorov1997b,on127.

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edgedthatwhen“themoleculartransitions begintosaturate,” theirequationwas no longersufficientfor estimating thelinewidth andpromisedthat“theeffects of this saturation will be considered in detail in alater paper.”71 Theabove exchange revealsthatthankstotheir commandofthe theory of self- oscillations,the Soviet team relied on amoreadvancedtheoretical understanding of themaser’s generation regime as an essentially nonlinear effect that required nonlinearequations forits description. TheAmericanpathtowards themaser can be characterized, by contrast,asgadget- or experiment-driven, relyinguponthe availabilityofhardwarewithadvancedcharacteristics inheritedfromthe wartime radarproject.Existingaccountsdescribe theinventionofthe maserbythe Co- lumbia University team as alongprocess with many experimental iterations,ad- justments,and agooddealoftweaking. Betweenthe “early-morning epiphany” on aparkbench in Washington,D.C., in thespringof1951, when Townes wrotehis firstnotes on what wouldeventuallybecomethe maser, andthe moment in April1954,whenGordonbroke into aseminar room announcing that he hadfinally obtainedthe long-sought oscillations,the anticipateddevice changedmultipletimes,fromageneratorof5mm wavestoaspectrometerand amplifierof1.25 cm waves. Thisevolution was long, costly,and tiresome,which prompted Townes’superiors at theColumbiaRadiation Laboratorytorecom- mend thetermination of theproject,because thechances of successseemed scanty.Townespersisted nevertheless, andthe eventual result vindicated hisre- solve. Thenovel device quickly attracted much attention, andyoung physicists showed theirinteresttomovetoColumbiaUniversity to learnthe “maser art.”72 Theexpressionalsoshows that theworkwas primarilyanexperimentalimprovi- zation with alifeofits own,asIan Hacking wouldhavesaid. To be more precise,wecan distinguishtwo levels of theory at work in this case. Thefirst is theEinsteintheoryofspontaneous andstimulatedemissionofradia- tion,the basis of thequantum theoretical analysisofspectraltransitions.73 This leveloftheorywas shared by both teams, whohad asimilar understandingthat thedevicereliedonanewsourceofenergy, theenergyofstimulatedquantum transitionsinthe molecularbeam. Thesecondlevel concerns theexplanation of thebehavioroftheradiation emittedbythe molecules andinteracting with the cavity andthe incoming beam.Atthislevel,the practice of thetwo teamswas quitedifferent. PhilosopherIan Hackinghas argued that theexistence of amaturetheoryisanimportant factor in influencing thechangingdynamics be- tweentheoryand experimentationovertime. When workinginacontextin whichawell-developed theory is available, scientists usually follow amorededuc- tive approach,whereas thelackofsuchtheoryprompts scientists towardsinduc- tive approaches andrelianceuponexperimentation as amoreautonomousen- deavor.74 Hacking’sdistinction seemstograsp wellthe apparent difference be- tweenthe Sovietand theAmericanroads towardsthe inventionofthe maser.

71 Gordon et al.1955, on 1268–1269. 72 Polykarp Kuschand Rabi putpressureonTownestoabandon the“moleculargenerator.” See: Forman 1992,on133.The term “maser art” is used by Bromberg 1991, on 24. 73 Einstein 1917. 74 Hacking1983, on 155–165.

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5. Conclusions

Theinvestigation of theparalleldiscovery/invention of themaser principleinthe USSR andthe USA in the1950s reveals importantcomparable trends notonly in thedevelopment of scientific ideasand researchprojects, butalsoinmuch more generalprocesses underlying theprofoundtransformationofscience during theearly Cold Warera.Basic questionsand problemsidentifiedand raised by his- torianswho have earlierstudied theAmericansideofthe story—such as thepene- tratingeffects of military patronage, gadgeteering andcompartmentalization, atransitiontobig scienceinstitutionsand mass training of scientists,ashiftfrom theideologyofpurescience to goal-orientedresearch, tensions betweenthe na- tional security stateand scientific internationalism,changes in theethos and social standing of scientists,the entanglement between open andclassifiedre- search,and thescientists’ denials of thelatter75—all thesemajor trends hadtheir deeply meaningful parallelsonthe Soviet side.Ananalysisofthese processesfrom acomparative perspectivesupportsthe conclusion aboutafundamentalconver- gencebetweenAmericanand Soviet scienceduringthe postwarperiod. This mutual approximationcannotbeunderstoodwithout taking into account thebroad social contextofthe time,namelyWorld WarIIand theCold War, andthe dramatically increasedrole of scienceinpoliticsand society, both in the East andinthe West,despite politicaland ideologicaldifferences.Someofthe powerfulsources of such converging tendencies canbecharacterized as structural: they reflectedsimilar lessonsderived from thewartime experience, thecommon attachment to progressive modernism, andthe rising importance of sciencefor themilitary. Othersources wererelationaland depended on mutual learning and frequent borrowing, whichcould sometimesbeacknowledgedopenly, andsome- timeshiddenorcamouflaged.Itisnot an uncommon phenomenon that rivals payincreased attentiontothe chiefenemy andoften endup, intentionally or as reflex,imitating each otherincertain methodsand behavioralaspects.The Cold Warcompetition in scienceand technologyexemplifies this tendency. In themaser case discussedhere, themostimportant structural similarity argu- ably came from theintimaterelationshipbetween scienceand themilitaryforged by WorldWar II.The fact that masers andlasers were notinventedearlier has puzzledsomescientists, because many of thenecessary concepts andexperimental methodshad alreadybeenathandbeforethe war, includingthe theory of stimu- latedemissionand thetechnologyofmolecular beams. Thepracticeofcombining advanced theories of quantum mechanicswithengineering skills andtasks also hadits rootsinthe interwar period,and some scientists,inparticular Vladimir Fabrikantinthe USSR, diddiscuss thepossibilityofusing stimulated emission forthe generation of radiation, butdid notsucceed in thepractical realizationof this idea at thetime.76 Themaser only becamepossibleafterthe war,withthe ex- perience physicists acquired whileworking in large-scalemilitaryprojects, with increasedmilitaryfunding forresearch, andwiththe knowledgeand technology createdinthe processofradar development.

75 Oreskes2014. 76 Lukishova2010.

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Therelationalconvergence during theColdWar offeredstrongmotivations forscientiststofollowattentivelythe work of theirrivals, butalsounprecedently strong obstacles createdbysecrecy andbybarrierstopersonalcommunications. Typically, as in themaser case,scientistshad accesstoopenlypublished worksby theother side, whichrepresented only theunclassifiedportion of theoverall re- search program,while trying to make informed guessesabout therestofthe re- search agenda andthe work that remained classified andhiddenfrompublic view.Thisartificialsituation,asifdeliberatelycreated by theIronCurtain at the height of theColdWar,helps demonstratethe theoreticalpoint that parallel in- ventionsand technology transfer couldtakeplace withoutmuchpersonalcontact andtacit knowledge, throughthe attentiveuse of formal publications andcom- munications,however censored andrestricted. Theconvergence of practicesstill left plentyofroomfor important differences in styleaswellasinsubstance.Inthe maserstory,one of ourmaintasks as histori- answas to uncoverthese differences, whichare sometimesobscuredbythe official storyofthe caseasaparalleldiscoveryand by thejoint award of theNobelprize. Ouraccount hasrevealedalternative heuristicpaths,background in differentsci- entificcultures, adifferent dynamics between theory andexperiment, andsignifi- cant disagreementsinconceptualizationand interpretation of themaser by the twoteams.Following thepersonalmeeting between Townes andProkhorov in 1955, theirsubsequentexchanges,and in thecourseofextensive furtherworkby many scientists on thedevelopment of masers andlasers,suchdisagreements were usuallyresolved, or superseded,and theirtraces made largelyinvisible.Theycan nevertheless be recoveredand understood with thehelpofarchivalsources. In many otherspecificcases,however,officialstories of theColdWar rivalry tended to adoptanapproachthatemphasizedoppositions,polarities, andmade convergencepaths invisibleorhiddenunder deliberately differentlabels. Histori- ansinfluencedbyideologicaldiscourse framed theirnarrative in such away as to downplay or brushaside comparable trendsand similarities. Theconvergingprac- ticesidentifiedinthisstudy hadbroader implications farbeyondthe maserstory andcertainly affected many otherresearchprojectsand developmentsinCold Warscience that arestill awaiting appropriatehistoricalanalysis. It is also impor- tant to note that theprocess of Cold Warconvergence was notlimited to science andtechnology,but extendedtoother areasofsociallife, with seriousconsequen- cesfor globaldevelopments in that era. Bringing theseprocesses to thefocus of historical attentioncan alsobring about areconceptualization of theacceptednar- rative of theCold War.

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