Stabilizing the Carrier-Envelope Phase of the Kansas Light Source

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Stabilizing the Carrier-Envelope Phase of the
Kansas Light Source

• Eric Moon
• Zuoliang Duan
• 11-9-2005

2
Outline

• Theoretical Description of the CE phase
• Why do we care about the CE phase?
• Can we control it? Yes! Heres how its done
  for the KLS and why it works.
• Single-Shot CE Phase Measurement Setup
• Results
• Future Plans

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Why do we care about controlling the change of
the carrier-envelope phase?

• Important for experiments utilizing few-cycle
  laser pulses, e.g. High Harmonic Generation
• Can use a stabilized frequency comb to perform
  spectroscopy.
• Related to this years Nobel prize!
• More applications to come!

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Results from Others

• Fortier et al1, have reported phase coherence
  times of 326 s.
• Witte et al2, have observed coherence times of
  500 s.
• Our group has observed coherence times of 85 s.
• The main goal is to achieve long term, on the
  order of hours, for running experiments.

1 Fortier et al, IEEE Journal Topics Quantum
Electron, Vol. 9, 1002-1010, 2003 2 Witte et
al, App. Physics B, 78, 5-12, 2004
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Theory1
Mode-locked lasers emit a regular train of
pulses.
For a single laser pulse
Envelope-function
Carrier-frequency
Carrier-envelope phase
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Theory1
Time-Domain Description of the Mode-Locked Pulse
Train
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Theory1
Due to material dispersion inside the laser
cavity, the CE phase changes.
The laser cavity length
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Theory1
Mode-Locked Pulse Train in the Time Domain
Mode-Locked Pulse Train in the Frequency Domain
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Frequency Comb and Laser Spectrum1
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Theory
The regular spacing of the frequency comb allows
access to the change of the carrier-envelope
phase.
How?
Can use a self-referencing technique!
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Theory1
The self-referencing technique requires an
octave-spanning spectrum of the laser.
Beating the second harmonic and fundamental
frequency combs of the laser yields a frequency
proportional to the change of the
carrier-envelope phase.
1 Fortier et al, IEEE J. Select. Topics Quantum
Electron., vol. 9, pp.1002-1010,2003.
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Theory

• The CE phase change can be controlled by locking
  the offset frequency, f0, to a known frequency.
• In the case of the KLS, f0 is set equal to
  one-quarter of the repetition rate of the
  oscillator.

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Experiment

• The KLS utilizes a Kerr-Lens Mode locked
  TiSapphire Oscillator emitting a 77 million
  pulses per second.
• The pulses are roughly 12 fs at the output of the
  laser and carry nJ energy per pulse.
• The oscillator is the starting point for the
  self-referencing technique.

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Why not use the amplifier output?
One reason Spectrum too narrow!
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KLS Oscillator Cavity
Pump
M5
Lens
A1
TiS
M1
ECDC-Module
M0
M6
M7
CP
M9
M3
OC
M8
M2
M10
M4E
Ultrashort Pulse Output
M4
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Stabilization Experimental Setup
offset frequency photodiode APD
focusing Lens f30mm
collimating Lens f30mm
HR1064nm mirror
focusing Lens f30mm
HR532nm mirror
BBO crystal
?/2
half wave plate 1064nm
polarizing beam-splitter 532nm
filter RG715
HR532nm mirror
?/2
half wave plate 532nm
?/2
HR532nm mirror
half wave plate 532nm
dichroic beam splitter HR 532nm,HT1064nm
polarizing beam-splitter 532nm
out-coupling objective f8.55mm
in-coupling objective f7.5mm
IR mirror
Silver mirror
PCF
?/2
half wave plate 800nm
Chirped mirror
Chirped mirror
grating 900lines/mm
From fs Laser
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532 nm
1064 nm
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1064 nm, Doubled in BBO Crystal
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Offset Frequency while Phase Locked
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Observation of Beat Note and Frequency Comb
frep-f0
f019.375MHz
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CE Phase Stability After Pulse Amplification2

• A second f-2f interferometer after the KLS
  amplifier provides a means for quantifying the CE
  phase stabilization stability.
• 10 of the KLS amplifier output is sent to the
  experimental setup.
• White-light is generated in a sapphire plate and
  a BBO crystal provides second-harmonic generation.

• 2 Baltuska et al.,IEEE J. Select. Topics
  Quantum Electron., vol. 9, pp. 972-989, 2003.

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Theory2
Interference between the white light and second
harmonic pulses
Phase of the Interference Signal
The shot-to-shot change of this phase can be
monitored by the second f-2f setup.

• 2 Baltuska et al.,IEEE J. Select. Topics
  Quantum Electron., vol. 9, pp. 972-989, 2003.

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Experiment
locking electronics
Pump
AO modulator 
M5
Lens
A1
TiS
M1
M0
M6
M7
HR IR mirror
BS 5050
CP
M3
OC
M8
M2
M4E
M4
nonlinear interferometer
spectral broadening
HR IR mirror
BS 91
stretcher
amplifier
compressor
1kHz fs laser
HR IR mirror
Single-shot phase measurement
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f-2f Interferometer after KLS Amplifier
1kHz fs laser
concave silver Mirrors f100mm
half wave plate
half wave plate
spectrometer
FCWL
two silver mirrors
SHG
VNA
VNA
sapphire d2.3mm
FCWL fundamental Continuum white light
silver mirrors
silver mirror
polarizer
f70mm
BBO
?T0.265ps
SHG
FCWL
532nm HR mirror
532nm HR mirror
f75mm
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Spectrum of the Second Harmonic generated in the
BBO Crystal
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Single-Shot Not Locked
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Line-Out of the Interference Pattern
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1 pulse
Phase-Locked
Not Phase-Locked
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51 pulses
Phase-Locked
Not Phase-Locked
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101 pulses
Phase-Locked
Not Phase-Locked
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200 pulses
Phase-Locked
Not Phase-Locked
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1000 pulses Phase-Locked
10000 pulses phase-locked
103000 pulses Phase-locked
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Summary

• The change of the carrier-envelope phase of the
  KLS has been stabilized.
• A technique for observing the carrier-envelope
  phase change shot-to-shot has been utilized.
• CE phase coherence times of up to 85 seconds have
  been observed.

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Future

• Send a slow CE phase drift signal from the second
  f-2f interferometer back to the locking
  electronics to achieve longer locking times.

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Thanks!

• Dr. Zenghu Chang
• Al Rankin
• KLS Members Mahendra Shakya, Shambhu Ghimire,
  Chris Nakamura, Chengquan Li, and Steve
  Gilbertson
• Zuoliang Duan for being a great partner on this
  project.
• Dr. Corwin and Dr. Washburn