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Stabilizing the Carrier-Envelope Phase of the Kansas Light Source. Eric Moon Zuoliang Duan 11-9-2005. Outline. Theoretical Description of the CE phase Why do we care about the CE phase? Can we control it? Yes! Here’s how it’s done for the KLS and why it works.

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Stabilizing the carrier envelope phase of the kansas light source

Stabilizing the Carrier-Envelope Phase of the Kansas Light Source

Eric Moon

Zuoliang Duan

11-9-2005


Outline
Outline Source

  • Theoretical Description of the CE phase

  • Why do we care about the CE phase?

  • Can we control it? Yes! Here’s how it’s done for the KLS and why it works.

  • Single-Shot CE Phase Measurement Setup

  • Results

  • Future Plans


Why do we care about controlling the change of the carrier envelope phase
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 year’s Nobel prize!

  • More applications to come!


Results from others
Results from Others carrier-envelope phase?

  • 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


Theory 1
Theory carrier-envelope phase?1

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.


Theory 11
Theory carrier-envelope phase?1

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.


Theory 12
Theory carrier-envelope phase?1

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.


Theory 13
Theory carrier-envelope phase?1

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.


Frequency comb and laser spectrum 1
Frequency Comb and Laser Spectrum carrier-envelope phase?1

[1] Fortier et al, IEEE J. Select. Topics Quantum Electron., vol. 9, pp.1002-1010,2003.


Theory
Theory carrier-envelope phase?

The regular spacing of the frequency comb allows access to the change of the carrier-envelope phase.

How?

Can use a self-referencing technique!


Theory 14
Theory carrier-envelope phase?1

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.


Theory1
Theory carrier-envelope phase?

  • 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.


Experiment
Experiment carrier-envelope phase?

  • The KLS utilizes a Kerr-Lens Mode locked Ti:Sapphire 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.


Why not use the amplifier output
Why not use the amplifier output? carrier-envelope phase?

One reason: Spectrum too narrow!


KLS Oscillator Cavity carrier-envelope phase?

Pump

M5

Lens

A1

Ti:S

M1

ECDC-Module

M0

M6

M7

CP

M9

M3

OC

M8

M2

M10

M4E

Ultrashort

Pulse

Output

M4


Stabilization Experimental Setup carrier-envelope phase?

offset frequency

photodiode

APD

collimating Lens

f=30mm

focusing Lens

f=30mm

focusing Lens

f=30mm

HR1064nm

mirror

HR532nm

mirror

BBO

crystal

λ/2

half wave plate 1064nm

polarizing

beam-splitter

532nm

filter RG715

HR532nm mirror

λ/2

half wave plate

532nm

λ/2

HR532nm mirror

half wave plate

532nm

dichroic beam splitter

HR 532nm,HT1064nm

polarizing

beam-splitter

532nm

out-coupling

objective

f=8.55mm

in-coupling

objective

f=7.5mm

IR mirror

Silver

mirror

PCF

λ/2

half wave plate 800nm

Chirped

mirror

Chirped

mirror

grating

900lines/mm

From fs Laser


532 nm carrier-envelope phase?

1064 nm


~1064 nm, Doubled in BBO Crystal carrier-envelope phase?


Offset frequency while phase locked
Offset Frequency while Phase Locked carrier-envelope phase?


Observation of beat note and frequency comb
Observation of Beat Note and Frequency Comb carrier-envelope phase?

frep-f0

f0=19.375MHz


Ce phase stability after pulse amplification 2
CE Phase Stability After Pulse Amplification carrier-envelope phase?2

  • 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.


Theory 2
Theory carrier-envelope phase?2

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.


Experiment carrier-envelope phase?

locking

electronics

Pump

AO modulator

M5

Lens

A1

Ti:S

M1

M0

M6

M7

HR IR mirror

BS

50:50

CP

M3

OC

M8

M2

M4E

M4

nonlinear

interferometer

spectral

broadening

HR IR mirror

BS 9:1

stretcher

compressor

amplifier

1kHz fs laser

HR IR mirror

Single-shot phase measurement


f-2f Interferometer after KLS Amplifier carrier-envelope phase?

1kHz fs laser

concave silver

Mirrors: f=100mm

half wave plate

half wave plate

spectrometer

FCWL

two silver mirrors

SHG

VNA

VNA

sapphire

d=2.3mm

FCWL: fundamental

Continuum white light

silver mirrors

silver mirror

polarizer

BBO

f=70mm

∆T=0.265ps

SHG

FCWL

532nm HR mirror

532nm HR mirror

f=75mm



Single shot not locked
Single-Shot: Not Locked carrier-envelope phase?


Line out of the interference pattern
Line-Out of the Interference Pattern carrier-envelope phase?


1 pulse carrier-envelope phase?

Phase-Locked

Not Phase-Locked


51 pulses carrier-envelope phase?

Phase-Locked

Not Phase-Locked


101 pulses carrier-envelope phase?

Phase-Locked

Not Phase-Locked


200 pulses carrier-envelope phase?

Phase-Locked

Not Phase-Locked


1000 pulses carrier-envelope phase?

Phase-Locked

10000 pulses

phase-locked

103000 pulses

Phase-locked


Summary
Summary carrier-envelope phase?

  • 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.


Future
Future carrier-envelope phase?

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


Thanks
Thanks! carrier-envelope phase?

  • 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


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