COMPACT BLUE-GREEN LASERS This book describes the theory and practical implementation of three techniques for the generation of blue-green light: nonlinear frequency conversion of infrared lasers,upconversionlasers,andwide-bandgapsemiconductordiodelasers. The book begins with a discussion of the various applications that have driven thedevelopmentofcompactsourcesofblue-greenlight.Part1thendescribesap- proachestoblue-greenlightgenerationthatexploitsecond-ordernonlinearoptics, includingsingle-pass,intracavity,resonator-enhancedandguided-wavesecondhar- monicgeneration.Part2,concernedwithupconversionlasers,investigateshowthe energyofmultipleredorinfraredphotonscanbecombinedtodirectlypumpblue- greenlasertransitions.Thephysicalbasisofthisapproachisthoroughlydiscussed andbothbulk-opticandfiber-opticimplementationsaredescribed.Part3describes wide-bandgapblue-greensemiconductordiodelasers,implementedinbothII–VI and III–V materials. The concluding chapter reflects on the progress in develop- ingtheselasersandusingtheminpracticalapplicationssuchashigh-densitydata storage,colordisplays,reprographics,andbiomedicaltechnology. CompactBlue-GreenLasersprovidesthefirstcomprehensive,unifiedtreatment ofthissubjectandissuitableforuseasanintroductorytextbookforgraduate-level coursesorasareferenceforacademicsandprofessionalsinoptics,appliedphysics, andelectricalengineering. william p. risk received the PhD degree from Stanford University in 1986. He joined the IBM Corporation in 1986 as a Research Staff Member at the Almaden ResearchCenterinSanJose,CA.Hisworkthereforseveralyearswasconcerned with the development of compact blue-green lasers for high-density optical data storage.Morerecently,hehasbeenactiveintheemergingfieldofquantuminforma- tion,andnowmanagestheQuantumInformationGroupattheAlmadenResearch Center. Dr Risk has authored or coauthored some 70 publications in technical journalsandconferenceproceedingsandholdsseveralpatents. timothy r. gosnell has been a technical staff member at Los Alamos National LaboratorysincereceivinghisPhDinphysicsfromCornellUniversityin1986.He haspursuedresearchactivitiesintheareasofbiophysics,nonlinearoptics,ultrafast laserphysicsandapplications,upconversionlasers,andmostrecentlyinthelaser coolingofsolidsandapplicationsofmagneticresonancetosingle-spindetection. He is the author of over 40 scientific papers and editor of several books in these fields.Inadditiontohisresearchworkinthepublicsector,DrGosnellhasrecently enteredtheprivatesectorasaseniorscientistforPixonLLC,aninformaticsstartup company that applies information theory and advanced statistical techniques to imageprocessingandtheanalysisofcomplexalgebraicsystems. arto v. nurmikko received his PhD degree in electrical engineering from the UniversityofCalifornia,Berkeley.FollowingapostdoctoralpositionattheMassa- chusettsInstituteof Technology,hejoinedBrownUniversityFacultyof Electrical Engineeringin1975.HeispresentlytheL.HerbertBallouUniversityProfessorof Engineering and Physics, as well as the Director of the Center for Advanced Ma- terialsResearch.ProfessorNurmikkoisaninternationalauthorityonexperimental condensedmatterphysicsandquantumelectronics,particularlyontheuseoflaser- basedmicroscopiesandadvancedspectroscopyforbothfundamentalandapplied purposes. His current interests are focused on optoelectronic material nanostruc- turesandtheirdevicescience.ProfessorNurmikkoistheauthorofapproximately 270scientificjournalpublications. COMPACT BLUE-GREEN LASERS W. P. RISK T. R. GOSNELL A. V. NURMIKKO    Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge  , United Kingdom Published in the United States by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521623186 © Cambridge University Press 2003 This book is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2003 ISBN-13 978-0-511-06604-7 eBook (NetLibrary) ISBN-10 0-511-06604-X eBook (NetLibrary) ISBN-13 978-0-521-62318-6 hardback ISBN-10 0-521-62318-9 hardback ISBN-13 978-0-521-52103-1 paperback ISBN-10 0-521-52103-3 paperback Cambridge University Press has no responsibility for the persistence or accuracy of s for external or third-party internet websites referred to in this book, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Contents Preface page xi 1 Theneedforcompactblue-greenlasers 1 1.1 Ashorthistoricaloverview 1 1.2 Applicationsforcompactblue-greenlasers 3 1.2.1 Opticaldatastorage 3 1.2.2 Reprographics 5 1.2.3 Colordisplays 6 1.2.4 Submarinecommunications 8 1.2.5 Spectroscopicapplications 12 1.2.6 Biotechnology 14 1.3 Blue-greenandbeyond 17 References 17 Part1 Blue-greenlasersbasedonnonlinearfrequencyconversion 20 2 Fundamentalsofnonlinearfrequencyupconversion 20 2.1 Introduction 20 2.2 BasicprinciplesofSHGandSFG 21 2.2.1 Thenatureofthenonlinearpolarization 21 2.2.2 Frequenciesoftheinducedpolarization 23 2.2.3 Thedcoefficient 28 2.2.4 Thegeneratedwave 30 2.2.5 SHGwithmonochromaticwaves 34 2.2.6 Multi-longitudinalmodesources 34 2.2.7 Pumpdepletion 38 2.3 Spatialconfinement 43 2.3.1 Boyd–KleinmananalysisforSHGwithcircular gaussianbeams 43 2.3.2 Guided-waveSHG 51 v vi Contents 2.4 Phasematching 56 2.4.1 Introduction 56 2.4.2 Birefringentphasematching 57 2.4.3 Quasi-phasematching(QPM) 71 2.4.4 Waveguidephasematching 90 2.4.5 Otherphasematchingtechniques 97 2.4.6 Summary 101 2.5 Materialsfornonlineargenerationofblue-greenlight 101 2.5.1 Introduction 101 2.5.2 Lithiumniobate(LN) 101 2.5.3 Lithiumtantalate(LT) 108 2.5.4 Potassiumtitanylphosphate(KTP) 110 2.5.5 Rubidiumtitanylarsenate(RTA) 115 2.5.6 OtherKTPisomorphs 119 2.5.7 Potassiumniobate(KN) 119 2.5.8 Potassiumlithiumniobate(KLN) 121 2.5.9 Lithiumiodate 123 2.5.10 Betabariumborate(BBO)andlithium borate(LBO) 124 2.5.11 Othermaterials 126 2.6 Summary 130 References 130 3 Single-passSHGandSFG 149 3.1 Introduction 149 3.2 Directsingle-passSHGofdiodelasers 151 3.2.1 Earlyexperimentswithgain-guidedlasers 151 3.2.2 Earlyexperimentswithindex-guidedlasers 154 3.2.3 High-powerindex-guidednarrow-stripelasers 156 3.2.4 Multiple-stripearrays 157 3.2.5 Broad-arealasers 160 3.2.6 Masteroscillator–poweramplifier(MOPA) configurations 161 3.2.7 Angled-gratingdistributedfeedback(DFB) lasers 169 3.3 Single-passSHGofdiode-pumpedsolid-statelasers 170 3.3.1 Frequency-doublingof1064-nmNd:YAG lasers 177 3.3.2 Frequency-doublingof946-nmNd:YAGlasers 177 3.3.3 Sum-frequencymixing 178 3.4 Summary 178 References 179 Contents vii 4 Resonator-enhancedSHGandSFG 183 4.1 Introduction 183 4.2 Theoryofresonatorenhancement 187 4.2.1 Theimpactofloss 189 4.2.2 Impedancematching 191 4.2.3 Frequencymatching 193 4.2.4 Approachestofrequencylocking 194 4.2.5 Modematching 207 4.3 Otherconsiderations 213 4.3.1 Temperaturelocking 213 4.3.2 Modulation 214 4.3.3 Bireflectioninmonolithicringresonators 215 4.4 Summary 220 References 220 5 IntracavitySHGandSFG 223 5.1 Introduction 223 5.2 TheoryofintracavitySHG 224 5.3 The“greenproblem” 229 5.3.1 Theproblemitself 229 5.3.2 Solutionstothe“greenproblem” 231 5.3.3 Single-modeoperation 235 5.4 BluelasersbasedonintracavitySHGof946-nm Nd:YAGlasers 245 5.5 IntracavitySHGofCr:LiSAFlasers 249 5.6 Self-frequency-doubling 250 5.6.1 Nd:LN 251 5.6.2 NYAB 252 5.6.3 Periodically-poledmaterials 253 5.6.4 Othermaterials 253 5.7 Intracavitysum-frequencymixing 253 5.8 Summary 255 References 256 6 Guided-waveSHG 263 6.1 Introduction 263 6.2 Fabricationissues 264 6.3 Integrationissues 269 6.3.1 Feedbackandfrequencystability 270 6.3.2 Polarizationcompatibility 276 6.3.3 Coupling 282 6.3.4 Controlofthephasematchingcondition 283 6.3.5 Extrinsicefficiencyenhancement 284 viii Contents 6.4 Summary 286 References 287 Part2 Upconversionlasers:Physicsanddevices 292 7 Essentialsofupconversionlaserphysics 292 7.1 Introductiontoupconversionlasersandrare-earth opticalphysics 292 7.1.1 Overviewofrare-earthspectroscopy 295 7.1.2 Qualitativefeaturesofrare-earthspectroscopy 296 7.2 Elementsofatomicstructure 303 7.2.1 Theeffectivecentralpotential 303 7.2.2 Electronicstructureofthefreerare-earthions 306 7.3 TheJudd–Ofeltexpressionforopticalintensities 324 7.3.1 Basicformulation 325 7.3.2 TheJudd–Ofeltexpressionfortheoscillator strength 329 7.3.3 Selectionrulesforelectricdipoletransitions 336 7.4 Nonradiativerelaxation 338 7.5 Radiationlessenergytransfer 341 7.6 Mechanismsofupconversion 345 7.6.1 Resonantmulti-photonabsorption 345 7.6.2 Cooperativeupconversion 348 7.6.3 Rateequationformulationofupconversionby radiationlessenergytransfer 357 7.6.4 Thephotonavalanche 360 7.7 Essentialsoflaserphysics 363 7.7.1 Qualitativepicture 364 7.7.2 Rateequationsforcontinuous-wave amplificationandlaseroscillation 365 7.8 Summary 382 References 383 8 Upconversionlasers 385 8.1 Historicalintroduction 385 8.2 Bulkupconversionlasers 397 8.2.1 UpconversionpumpedEr3+ infraredlasers 398 8.2.2 Er3+ visibleupconversionlasers 410 8.2.3 Tm3+ upconversionlasers 420 8.2.4 Pr3+ upconversionlasers 424 8.2.5 Nd3+ upconversionlasers 425 8.3 Upconversionfiberlasers 427 8.3.1 Er3+ fiberlasers;4S3/2 → 4I15/2 transition at556nm 433 Contents ix 8.3.2 Tm3+ fiberlasers 436 8.3.3 Pr3+ fiberlasers 445 8.3.4 Ho3+ fiberlasers,5S → 5I transition 2 8 at∼550nm 455 8.3.5 Nd3+ fiberlasers 457 8.4 Prospects 458 References 460 Part3 Blue-greensemiconductorlasers 468 9 Introductiontoblue-greensemiconductorlasers 468 9.1 Overview 468 9.2 Overviewofphysicalpropertiesofwide-bandgap semiconductors 470 9.2.1 Latticematching 470 9.2.2 Epitaxiallateralovergrowth(ELOG) 472 9.2.3 Basicphysicalparameters 474 9.3 Dopinginwide-gapsemiconductors 475 9.4 Ohmiccontactsforp-typewide-gapsemiconductors 478 9.4.1 Ohmiccontactstop-AlGaInN 479 9.4.2 Newapproachestop-contacts 481 9.4.3 Ohmiccontactstop-ZnSe:bandstructure engineering 482 9.5 Summary 484 References 484 10 Devicedesign,performance,andphysicsofopticalgainofthe InGaNQWvioletdiodelasers 487 10.1 Overviewofblueandgreendiodelaserdeviceissues 487 10.2 TheInGaNMQWvioletdiodelaser:Designand performance 488 10.2.1 Layereddesignandepitaxialgrowth 488 10.2.2 Diodelaserfabricationandperformance 496 10.3 PhysicsofopticalgainintheInGaNMQWdiodelaser 501 10.3.1 OntheelectronicmicrostructureofInGaNQWs 506 10.3.2 Excitoniccontributionsingreen-blue ZnSe-basedQWdiodelasers 509 10.4 Summary 513 References 513 11 Prospectsandpropertiesforvertical-cavitybluelightemitters 517 11.1 Background 517 11.2 Opticalresonatordesignandfabrication:Demonstration ofoptically-pumpedVCSELoperationinthe 380–410-nmrange 518