Table Of ContentGraduate Texts in Physics
Ursula Keller
Ultrafast Lasers
A Comprehensive Introduction
to Fundamental Principles with
Practical Applications
Graduate Texts in Physics
SeriesEditors
KurtH.Becker,NYUPolytechnicSchoolofEngineering,Brooklyn,NY,USA
Jean-MarcDiMeglio,MatièreetSystèmesComplexes,BâtimentCondorcet,Université
ParisDiderot,Paris,France
SadriHassani,DepartmentofPhysics,IllinoisStateUniversity,Normal,IL,USA
MortenHjorth-Jensen,DepartmentofPhysics,Blindern,UniversityofOslo,Oslo,
Norway
BillMunro,NTTBasicResearchLaboratories,Atsugi,Japan
RichardNeeds,CavendishLaboratory,UniversityofCambridge,Cambridge,UK
WilliamT.Rhodes,DepartmentofComputerandElectricalEngineeringandComputer
Science,FloridaAtlanticUniversity,BocaRaton,FL,USA
SusanScott,AustralianNationalUniversity,Acton,Australia
H.EugeneStanley,CenterforPolymerStudies,PhysicsDepartment,Boston
University,Boston,MA,USA
MartinStutzmann,WalterSchottkyInstitute,TechnicalUniversityofMunich,
Garching,Germany
AndreasWipf,InstituteofTheoreticalPhysics,Friedrich-Schiller-UniversityJena,
Jena,Germany
GraduateTextsinPhysicspublishescorelearning/teachingmaterialforgraduate-and
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derivations,experimentsandapplications(asrelevant)fortheirmasteryandteaching,
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syllabisufficientlytoserveasrequiredreading.Theirdidacticstyle,comprehensive-
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Ursula Keller
Ultrafast Lasers
A Comprehensive Introduction to
Fundamental Principles with Practical
Applications
UrsulaKeller
PhysicsDepartment,
UltrafastLaserPhysics
ETHZürich
Zürich,Switzerland
ISSN1868-4513 ISSN1868-4521 (electronic)
GraduateTextsinPhysics
ISBN978-3-030-82531-7 ISBN978-3-030-82532-4 (eBook)
https://doi.org/10.1007/978-3-030-82532-4
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Preface
This graduate-level textbook starts with Maxwell’s equations. If the reader finds
thisreasonable,thisbookshouldbehelpful.Focusingonultrafastsolid-statelaser
oscillators, the book provides detailed derivations of most key equations. Subjects
such as nonlinear pulse propagation and frequency metrology are discussed, but
only to a level that should help the researcher to get started in this field. Certain
topics,suchasfiberlasers,areleftforothermorequalifiedcolleaguestoauthor.In
general, I would like to encourage more such textbooks, with detailed derivations
critical for new research fields, as this would greatly assist the current and new
generations of researchers.
Thisbookistheproductofnearly30yearsofresearchandteachinginultrafast
laser physics at ETH Zurich, Switzerland. I started my academic career in March
1993 as an associate tenured professor in physics at ETH Zurich, and taught my
firstcourseoneyearlater,in1994.Inadditiontoeducatingnewgraduatestudents,
onere-discovers,andmustevenre-learn,muchofthesubjectmatteragain.Ifound
that these re-learned basics ultimately strengthened my own research efforts, in
addition to engaging excellent students and postdocs.
Manystudentsofthiscoursewentontobecomemembersofmyresearchgroup,
and many have contributed to this textbook over the years. As this book goes to
press,Ihavegraduated87Ph.D.students,andexpecttohavegraduated100bymy
mandatoryretirementfromETHin2024.Scatteredacrossindustry,frommultina-
tionalcompaniestostart-ups,andacademiaincludinganumberofprofessorships,
they have strongly encouraged me to complete this textbook and will hopefully
use it to continue teaching the next generations in ultrafast lasers!
I have been active in ultrafast lasers for more than 30 years and have added,
on occasion, personal insights into how some of our progress was made. These
historical perspectives, based solely on my own experiences, attempt to show
how innovation and new discoveries come about. In any event, I encourage new
researchers to simply take action and push the knowledge horizon. It has been a
great experience for me.
Starting and finishing a textbook is always challenging. In this case, the covid
pandemicgetscreditforprovidingtheextrarequiredpush.OnMarch16,2020,all
labs at ETH Zurich were shut down. Now forced to work from home, I finalized
v
vi Preface
a plan for the textbook by April 6, and signed the book contract with Springer
on May 4, 2020. I also overcame my career-long resistance to learning LaTeX
(suchatextbookfilledwithequationsgoeswellbeyondthecapabilitiesofnormal
word processors I discovered), so with very good support from Springer, my old
wordfileswereconvertedintoLaTeXfiles,andwestartedthismorethanone-year
project.
My first taste of ultrafast lasers started during my Ph.D. at Stanford Univer-
sity. My ETH Diplom (master’s equivalent) in physics had me well-prepared with
respect to the basic physics and math. Key coursework at Stanford was often
taught by the authors themselves, and laid the necessary groundwork for lasers
and other essential topics. A standout in my memory was Prof. Anthony Sieg-
man with his laser textbook (published 1986), the go-to reference for most laser
challenges and issues. There were many other excellent professors and courses
in lasers and optics at Stanford. For example, we learned about Fourier trans-
forms from Ronald Bracewell, nonlinear optics from Steve Harris and Robert
Byer, diode-pumped solid-state lasers from Byer, and microwave measurement
techniques and laser noise characterization from my Ph.D. advisor Dave Bloom.
A visiting professor Geraldine Kenney-Wallace—the first woman professor I had
ever met in my education—encouraged me to join this very young and energetic
professorinelectricalengineering.BetweenmybuddingEnglishskillsandDave’s
electrical-engineeringtalk,usingforeign-soundingtermssuchasdBm,noisefloor,
and sampling, I barely understood what his research was about. Nonetheless, his
positive energy and maybe some further encouragement from Geraldine, and my
strong physics background from ETH, convinced him to offer me a Ph.D. student
position,andmetotakeit.AdecisionIneverregretted.Alloftheteachingofthese
great mentors at Stanford, in one way or another, is integrated into this textbook.
For those new to photonics, this Stanford-Ginzton Lab thread runs all the way
back to the origin of lasers. Anthony Siegman was the Ph.D. advisor of Steve
Harris. Harris supervised Byer and Bloom, my supervisor. Siegman is my aca-
demic great-grandfather, and the academic great-great grandfather for my Ph.D.
students. So if you happen to be studying under one of my former students, Sieg-
manisyourgreat-cubed(great3)-grandfather.TheodoreH.Maiman,whobuiltand
demonstrated the very first laser in 1960, learned key skills as a Ph.D. at Stan-
ford. There has been a long tradition in understanding and building better lasers,
cultivated in Ginzton Labs for many decades.
AftermyPh.D.,IjoinedAT&TBellLabs(Homdel,NJ)asaMemberofTech-
nical Staff (MTS), where I continued working with excellent scientists. One of
the last permanent hires for many years due to an economic recession, I was
empowered to pursue my own independent research efforts, with the guideline:
Dosomethingdifferentfromeverybodyelse,butitbetterbegood.ThisiswhereI
inventedtheSESAMforpassivemodelocking,andhowthishappenedisexplained
in this textbook. A key asset was the state-of-the-art semiconductor epitaxial
growth expertise at Bell Labs. Some of my great role models there were Chuck
Shank (who hired me, but had left for an academic position before I arrived),
DanielChemla,DaveAuston,DavidA.B.Miller,RickFreeman(whoofferedme
Preface vii
an MTS position in Murray Hill, based on a talk at my first Gordon Conference
duringmyPh.D.),somegreatofficeneighborsTedWoodwardandKeithGoossen,
and my first postdoc Gloria Jacobovitz Veselka, still a good friend to this day.
My work at Bell Labs, combined with growing political pressure to hire more
women professors at ETH Zurich, resulted in an unexpected call asking me to
consider a position in the physics department at ETH Zurich. At that time, many
professorsinSwitzerlandhadfirstbeenintheU.S.,veryoftenwithapostdocoran
MTS position at Bell Labs or at IBM Research Labs, in photonics, quantum elec-
tronics,orlasers.Followingthispattern,mynearlyfouryearsasMTSatBellLabs
had prepared me well, and resulted in an offer for a tenured position. The profes-
sorship meant I could multiply my work with many excellent Ph.D. students and
postdocs,andIknewexactlywhatIwantedtodo.Atfirstlackingsufficientclean-
room and semiconductor growth facilities at ETH Zurich, we eventually achieved
a critical mass of new professors and could fund and launch a shared ETH tech-
nologyplatform,theFIRSTlab.FIRSTstandsforFrontierInResearch:Spaceand
Time, and became a key building block for my research work here.
I came to greatly appreciate the warm welcome after arriving in Switzerland
from leaders in the European laser community, including Profs. Günter Huber,
OrazioSvelto,DavidHanna,andGerdLeuchs.PeerreviewformySwissproposals
ismostlybasedoninternationalexpertsandfortunatelywasoftenhighlyranked(in
SwitzerlandandatETHZurich,however,therewas,toooften,asurprisinglyless-
than-welcomefeedback,whichmaybethetopicofafuturebook).Intheend,the
resourcesatETHweresignificantlybetterthanatmanyotherplaces,andIalways
focusedonexcellentresults.Asanexperimentalist,mostofmylaserresultscould
be measured, and this helped me to continue to push the frontier in ultrafast laser
physics by always working on better lasers that had useful applications.
Inthemeantime,theleadershipinultrafastlasers,andindeedmanyothertypes
of lasers, has shifted from mostly in the U.S. to Europe, with key contributions
from many European universities and institutions, and innovative products from
many European start-ups. This has been a great trend to witness, and I can only
hope to continue to see it strengthen in the coming decades. Thinking back to my
start in lasers at Stanford in mid-80s, and looking at the technical performance
routinelyachievedtheninresearchlabsandmanycommercialproducts,thescope
oftoday’slaserperformanceinoutputpower,pulseenergy,pulsewidth,repetition
rate,timing,andevenopticalphasestability,isjaw-droppinglystunning.Manyof
thesefeatureswereconsideredimpossible,evenbysomeoftheleadersinthefield
of the time. In the meantime, we, and by this, I mean contributions of thousands
of scientists and engineers worldwide, have made it happen.
Ihopethatthistextbook,andthemanystudentsandresearchersIhavehadthe
pleasureandopportunitytoteachandlearnfrom,continuetocontribute.Iamsure
thatultrafastlasersstillholdmanyusefuldevelopments,applications,andpositive
surprises for the future.
Zürich, Switzerland Ursula Keller
Acknowledgements
I would like to acknowledge the many contributions from my current and for-
mer Ph.D. students and postdocs. The list of Ph.D. students is summarized below.
Three new Ph.D. students starting in 2020 (i.e., Sandro Camenzind, Erik de Vos,
and Alexander Nussbaum-Lapping) had, as their first assignment, a last check on
the current textbook while they were also learning the basics. I am very grateful
for their careful reading. Many postdocs over the years significantly contributed
to this textbook such as Franz Kärtner (1993–1997), Luigi Brovelli (1993–1995),
Rüdiger Paschotta (1997–2005), Günter Steinmeyer (1998–2002), Markus Haiml
(2002–2005),ThomasSüdmeyer(2005–2011),ClaraSaraceno(2013–2016),Chris
Phillips (since 2012), and Lukas Gallmann (since 2006). Professor Lukas Gall-
mann also took over the lecturing for many years during my additional leadership
duties within the NCCR MUST. Special thanks also goes to my MBE growers
in the FIRST lab, especially for the great long-lasting support from Dr. Matthias
Golling since 2002. I also would like to thank Stephen Lyle for his support in
LaTeX for the final preparation of this textbook and my former Ph.D. student
Birgit Gallmann-Schenkel for help in improving the growing lecture notes with
temporary assignments between 2006 and 2009.
Forourneweffortinfrequencymetrology(Chap.12)Iwouldliketoacknowl-
edge the great collaborations with Harald R. Telle (PTB Braunscheig, Germany),
and Prof. Pierre Thomann and his senior group leader Dr. Stephane Schilt (Uni-
versity Neuchatel, Switzerland). Especially the great tutorials from the group of
Prof. Thomann have been used in Chap. 12. In addition we had many other inter-
national collaborations which resulted in joint publications referenced throughout
this textbook.
A special thank you goes to my graduate students as follows (with year of
Ph.D. exam): Daniel Kopf (1996), Bernd Braun (1996), Isabella Jung (1997),
Regula Fluck (1998), Clemens Hönninger (1998), Nicolai Matuschek (1999),
Sebastian Arlt (1999), Dirk Sutter (2000), Gabriel Spühler (2000), Jürg Aus der
Au (2000), Jens Kunde (2000), Markus Haiml (2001), Marc Achermann (2001),
RetoHäring(2001),LukasGallmann(2001),LukasKrainer(2002),ThomasSüd-
meyer (2003), Felix Brunner (2004), Birgit Schenkel (2004), Alex Aschwanden
(2004), Florian Helbing (2004), Steve Lecomte (2005), Wouter Kornelis (2005),
ix
x Acknowledgements
Christoph Hauri (2005), Edith Innerhofer (2005), Dirk Lorenser (2005), Anastas-
siaGosteva(2005),RachelGrange(2006),ArneHeinrich(2006),AdrianSchlatter
(2006), Simon Zeller (2006), Valeria Liverini (2007), Sergio Marchese (2007),
Andreas Rutz (2008), Christian Erny (2008), Petrissa Eckle (2009), Deran Maas
(2008), Aude-Reine Bellancourt (2009), Florian Schapper (2009), Max Stumpf
(2009), Andreas Oehler (2009), Mirko Holler (2009), Benjamin Rudin (2010),
CyrillBär(2010),AdrianPfeiffer(2011),EkatarinaVorobeva(2011),MartinHoff-
mann(2011),OliverHeckl(2011),SelinaPekarek(2011),ClemensHeese(2012),
Valentin Wittwer (2012), Matthias Weger (2012), Clara Saraceno (2012), Oliver
Sieber (2013), Wolfgang Pallmann (2013), Reto Locher (2013), Mazyar Sab-
bar (2014), Christian Zaugg (2014), Jens Herrmann (2014), Robert Boge (2014),
AlexanderKlenner(2015),CiniaSchriber(2015),MarioMangold(2015),Florian
Emaury (2015), Sebastian Heuser (2015), Benedikt Mayer (2015), Andre Lud-
wig(2016),CorneliaHofmann(2016),SandroLink(2017),LamiaKasmi(2017),
AndreasDiebold(2018),AlineMayer(2018),DominikWaldburger(2018),Jannie
Vos (2018), Nicolas Bigler (2018), Cesare Alfieri (2018), Mikhail Volkov (2018),
Fabian Schläpfer (2019), Benjamin Willenberg (2019), Justinas Pupeikis (2019),
Ivan Graumann (2019), Francesco Saltarelli (2020), Luca Pedrelli (2020), Nadja
Hartmann (2020), Stefan Hrisafov (2020), Jacob Nürnberg (2020), Jaco Fuchs
(2021). My current Ph.D. students: Fabian Brunner, Leonard Krüger, Arthur Nie-
dermayr, Lukas Lang, Pierre-Alexis Chevreuil, Jonas Heidrich, Marco Gaulke,
Carolin Bauer, Erik de Vos, Alexander Nussbaum-Lapping, Sandro Camenzind,
Moritz Seidel.
I am particularly grateful for the excellent funding support in Switzerland,
within ETH Zurich, the Swiss National Science Foundation, the Innosuisse, and
from special programs such as NCCR quantum photonics and NCCR MUST. For
MUST I was also serving as a director. Additional support is also acknowledged
fromEUfundingprograms,especiallythetwoERCadvancedgrants.Myeffortsat
ETH Zurich for a joint new technology platform (i.e., FastLab) based on ultrafast
lasers is still an ongoing effort and I hope that this FastLab will become possible
soon to better empower the next generation of researchers in ultrafast science.
Last but not least, a very special thank you goes to my family, my husband
Kurt Weingarten, and our two sons Matthew and Christopher. My husband and I
focusedoncombiningbothourcareersandraisingourtwochildrentogether.And
manythankstoourgreaterfamilyandfriendssupportnetwork,astheywereoften
crucial when we had to ask for additional working time under difficult or tight
deadlines. In the end, our sons flourished and are currently completing degrees at
ETH Zurich.
Zürich, Switzerland Ursula Keller
April 2021
