A New Generation of High-Power, Waveform Controlled, Few-Cycle Light Sources

242 Pages·2019·26.432 MB·English

by  Marcus Seidel

Springer Theses
Recognizing Outstanding Ph.D. Research
Marcus Seidel
A New Generation
of High-Power,
Waveform Controlled,
Few-Cycle
Light Sources
Springer Theses
Recognizing Outstanding Ph.D. Research
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Marcus Seidel
A New Generation
of High-Power, Waveform
Controlled, Few-Cycle Light
Sources
Doctoral Thesis accepted by
the Max Planck Institute of Quantum Optics,
Garching, Germany
123
Author Supervisor
Dr. Marcus Seidel Prof. Dr. FerencKrausz
Institut deScience etd’Ingénierie MaxPlanckInstitute ofQuantum Optics
Supramoléculaires Garching,Germany
Strasbourg, France
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-10790-1 ISBN978-3-030-10791-8 (eBook)
https://doi.org/10.1007/978-3-030-10791-8
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’
Supervisor s Foreword
Exploitingtheuniquepropertiesofcoherentlaserlighthasbecomeessentialinour
modernsociety.High-speedInternetisenabledbyopticallyencodeddatapackages.
Laser material processingis, for instance, indispensableintheautomotiveindustry
or in display manufacturing. Medical applications such as eye surgeries, cancer
diagnosis, and treatment have been established. Yet, the development of laser
technology, promising new exciting applications, is ongoing with no end in sight.
One of the unique properties of coherent light is its compressibility to extreme
timescales of femto- (10−15 s) or even attoseconds (10−18 s), resulting in two
outstanding properties: First, ultrashort laser pulses are capable of tracing all
motionsofelementarymatteroutsidethenucleusinrealtime.Second,laserpulses
can reach power levels of large-scale power plants (partially even orders of mag-
nitudemore)foranultrashorttimeandthusareabletoprovidethehighestdegreeof
control over molecules, atoms, and electrons.
Althoughfemtosecondpulsesweredemonstrated inthe1970sforthe firsttime,
their wide applicability was enabled by the progress in the development of
solid-state lasers. In particular, the demonstration of the Kerr-lens mode-locked
Ti:sapphire oscillator in 1990 set a milestone for ultrafast laser development.
Whereas Ti:sapphire lasers have enabled full control over the optical waveform,
lightpulsegenerationwithdurationsofaboutasinglecarrierwavecycleandoctave
spanning bandwidths as well as attosecond pulse formation via high harmonic
generation, it remains elusive to trigger these spectacular phenomena at least a
million times per second.
Here, the “new generation of high-power, waveform controlled few-cycle light
sources” comes into play. Peak and average power-scalable diode-pumped solid-
state lasers, e.g. thin-disk lasers, can nowadays readily deliver up to kilowatts of
optical average power. However, the available gain media are only capable of
generating pulses with at best about 100 fs of duration, being far away from the
few-cycle limit where full light field control becomes important and strong field
effects are attainable.
v
vi Supervisor’sForeword
This dissertation demonstrates ways of combining the best of both worlds.
Marcus Seidel achieved few-cycle pulse generation and waveform control, prop-
erties of the Ti:sapphire technology, from a high-power Kerr-lens mode-locked
thin-disk laser oscillator.
The workfirst brieflylooks backtomore than 50 years ofultrashortpulse laser
generation. By doing so, methods and goals of the technical development are
highlighted, setting the road map for 5 years of Ph.D. work. At the same time, an
introduction for newcomers to the field, which points out general ideas of the
research subject, is provided. In the experimental chapters, three major achieve-
ments are described: First, the implementation of an amplification-free multi-watt
few-cycle pulse source that can be carrier-envelope-phase stabilized yielding full
controlovertheopticalwaveformisreported.Second,power-scalablemethodsare
demonstratedwhichpresenttheprospectofwaveformcontrolledfew-cyclesources
with hundreds of watts average power. Third, frequency conversion to the
mid-infraredspectralregionisaccomplishedatunprecedentedhighaveragepowers.
This presents an excellent example for applications of the new powerful ultra-
short laser pulse sources. Experiments with low yield, for instance frequency
conversion to the ultraviolet or mid-infrared, will strongly benefit from the sig-
nificantlyincreasedpowerlevelsoftheultrafastnear-infrareddrivingsources.This
in turn promises novel applications in both fundamental and applied sciences. For
instance, my research group is exploring ways to employ this advanced laser
technology in early cancer diagnosis.
In this respect, Marcus Seidel’s Ph.D. thesis presents a very good reference for
laser scientists working on the forefront of ultrafast optics as well as graduate
students who are new to the field. Additionally, the reported results will have an
impact on multi-disciplinary research topics where short pulse lasers serve as
essential instruments.
Garching, Germany Prof. Dr. Ferenc Krausz
December 2018
Abstract
With the advent of peak and average power-scalable femtosecond lasers, in par-
ticular mode-locked thin-disk oscillators, the need for equally scalable pulse
compression, carrier-envelope-phase stabilization, and frequency conversion
schemes arose. These techniques have been routinely applied to lower average
power ultrafast lasers, for instance, the widely used Ti:sapphire based ones. But
they had to be reinvented for cutting-edge femtosecond sources with 100 W-level
average and 10 MW-level peak powers.
This dissertation presents how pulses emitted from a 45-W-average power
mode-lockedthin-diskoscillatorwerecompressedforthefirsttimetoadurationof
onlyafewopticalcycles.Pulsesasshortas7.7fswereattainedfromtwosequential
spectral broadening and chirped mirror pulse compression stages.
The same light source was also the first thin-disk oscillator, and simultaneously
the first oscillator with an average power of more than 10 W, which was
carrier-envelope-phase stabilized. Two stabilization methods are presented: The
first one utilized intracavity loss modulation by means of an acousto-optic modu-
lator. This resulted in 125 mrad in-loop and 270 mrad out-of-loop residual phase
noise. The second one employed pump diode current modulation by means of an
auxiliary power supply. This approach yielded a 390 mrad residual in-loop phase
noise.
Whereas the presented carrier-envelope-phase stabilization schemes are
power-scalable,thescalability oftheinitial few-cycle pulse generation approachis
restricted by the damage threshold of solid-core photonic crystal fiber. The thesis
reports in detail on the limitations of these fibers with respect to maximally
transmittablepeakpowersandattainablespectralbroadeningfactors.Moreover,an
alternative approach utilizing hollow-core Kagomé-type photonic crystal fibers is
demonstrated. A double-stage broadening and compression setup yielded pulse
durations of only 9.1 fs, but also showed a significant intensity noise increase in
comparison with the thin-disk oscillator output.
Therefore, spectral broadening in bulk crystals was studied. By exploiting the
optical Kerr effect, spectra with Fourier transform limits of 15 fs were achieved,
opening the perspective for all solid-state spectral broadening in bulk material.
vii
viii Abstract
Simulation results for a sequence of thin Kerr media predict a good power effi-
ciency of the method. Furthermore, an experimental realization of pulse compres-
sionfrom190fspulseswith90Waveragepowerto30fspulseswith70Waverage
power in self-defocusing BBO crystals is reported. The presented comprehensive
study on spectral broadening and pulse compression techniques paves the way to
few-cyclepulsegeneration athundredsofMWpeakpowerandhundredsofWatts
average power.
Eventually, the dissertation addresses the issue of transferring broadband,
powerful spectra to a wavelength region with a huge variety of characteristic
molecular absorptions—the mid-infrared. Frequency down-conversion via optical
parametricamplificationresultedinradiationwithupto5Wat4.1lmand1.3Wat
8.5 lm, corresponding to an order-of-magnitude average power increase for
compact femtosecond light sources operating at wavelengths longer than 5 lm.
In addition to the power measurements, both wavelength tunability and super-
continuum generation by means of cascaded quadratic nonlinearities are reported,
resulting in overall spectral coverage from 1.6 to 11 lm with power spectral
densities exceeding 1 lW/cm−1 over the entire range.
The pulse compression and carrier-envelope-phase stabilization schemes
demonstrated in this dissertation will serve as fundamental techniques for the fur-
ther development of a new generation of waveform-controlled few-cycle pulse
lasers which are capable of triggering extreme nonlinear effects at unprecedented
average powers and repetition rates. The multi-octave spanning, mid-infrared
femtosecond source offers exciting opportunities for molecular fingerprinting, in
particular by means of frequency up-conversion and field-sensitive techniques as
well as frequency comb spectroscopy.
Preface
The year 2018 was special in the history of femtosecond laser technology. On
December 10, the Nobel Prize in Physics was awarded to Gérard Mourou and his
former Ph.D. student Donna Strickland “for their method of generating
high-intensity, ultrashort optical pulses.” In their joint paper from 1985, the sci-
entists proposed and demonstrated the concept of chirped pulse amplification. By
means of this still very common optical amplification method, Strickland and
Mourou successfully tackled an ever-present dilemma in femtosecond laser tech-
nology: Owing to the compression of light energy to ultrashort time scales,
extremelyhighinstantaneousopticalpowerscanreadilybeachievedandnonlinear
effects in any material are triggered. On the one hand, these nonlinearities are
essential for femtosecond pulse applications. On the other hand, they are detri-
mental for femtosecond pulse generation as they induce distortions of the laser
beam or even material damage. Today, the lasers employing Strickland’s and
Mourou’s invention have found a large variety of applications in fundamental
science and industry. This demonstrates the significance of femtosecond laser
developmentwhichisstillasdemandedasinthe1980s,andtheolddilemmaisstill
challenged—yet on a significantly higher level.
The title of this dissertation: “A new generation of high-power, waveform
controlled,few-cyclelightsources”,alreadyindicatesthatscalingupopticalpower
hasnotlostitstopicality.WhereasStricklandandMourouachievedabreakthrough
in increasing instantaneous power, the currently developed femtosecond laser
technology aims for combining both high instantaneous and high average power.
This poses new challenges on retaining unique ultrashort light pulse properties at
anyopticalpowerlevel. Suchpropertiesarethecompressionoflightenergy down
toafewelectricfieldcyclesandtheprecisecontrolofthelightfieldwaveform.Ina
nutshell,thiswasthesubjectoftheresearchIconductedbetweenAugust2012and
June 2017 at the Laboratory for Attosecond Physics in the group of Prof. Ferenc
Krausz.
The first version of this thesis was submitted in February 2018. Only minor
changes of the text have been made since then. Consequently, some novel devel-
opments might be missing in Sect. 1.2 (History) or Chap. 5 (Outlook). The large
ix