Optical Amplifier Development (for Stochastic Cooling)

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Optical Amplifier Development (for Stochastic
Cooling)

• Franz X. Kaertner
• MIT-Optics and Quantum Electronics Group

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Outline
I. Amplifier Requirements for Optical
Stoachastic Cooling II. Optical Parametric
Amplification (OPA) III. Cavity Enhanced Optical
Parametric Amplification IV. Precise Dispersion
Compensation
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Amplifier Requirements for Optical Stoachastic
Cooling
1-100mJ
20ps, 20-30 MHz repetition rate
Dispersion free 30-40 dB Amplification

• Ultra broadband amplification
• Group delay control to a fraction of an optical
  cycle
• ? Large amplification in a short medium?
  Optical Parametric Amplification

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Optical Parametric Amplification
Idler
Pump
Signal
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Periodically Poled Lithium Niobate (PPLN)
For L30.4 mm
Fuji et al. Ultrafast Optics, Sept. 2005, Nara,
Japan
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Large Gain
20-100 ps, 1064mm Laser 30 MHz, 2-5mJ
PPLN
Pump laser 100 ps, 60-80 W average power OPA
non-saturated 0.1 conversion ? 6-8 W output
power
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Cavity Enhanced OPA
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(No Transcript)
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Single-Pass Parametric Amplification
PPLN Crystal with 6 gratings
30 ps, 1064mm Laser 1kHz, 1mJ
To OSA
Pump pulses
Experimental Setup
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Single-Pass Parametric Amplification
3.21mV
7.09V
Gain 7.09V/3.21mV 2200
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Cavity Enhanced OPCPA
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Current Enhancement Cavity Setup
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Dispersion of 2mm Lithium Niobate
1 cycle _at_ 2mm (6.7 fs)
0.1 cycle
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Double-Chirped Mirrors
Chirped Mirrors R. Sizpöcs, et al. OL 19, 201
(1994).
Mirror-Pairs Covering One Octave
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DCM-Pairs Covering One Octave (Fabrication by Ion
beam sputtering, Nanolayers)
Pump Window
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Broadband, Prismless Tisapphire Laser
1mm BaF2
f 10o
Laser crystal 2mm TiAl2O3
OC
PUMP
L 10 cm
Silver mirror
BaF2 - wedges
Base Length 15cm for 200 MHz Laser
BaF2 highest ratio of second to third order
dispersion ? repetition rate scaling
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Spectra from 80 MHz and 150 MHz laser with
broadband OC

Matos et al., OL 29, 1683 (2004)
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Conclusion
An Ultrabroadband Optical Amplifier for Optical
Stochastic Cooling can be built using PPLN and
OPA at 2 mm Dispersion in this wavelength range
is low and can be precisely compensated by
chirped mirrors (maybe even with prisms)
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Thermo-Optic Properties of YAG
Data is from new material property measurements
performed at or procured by MIT Lincoln
Laboratory R. L. Aggarwal et. al., Photonics
West (2005) Previously published values for
material properties R. Wynne et. al., Applied
Optics 38, 3238 (1999). G. A. Slack et. al.,
Phys. Rev. B 4, 592 (1971).
Thermal Conductivity (W/m K)
CTE (ppm/K), dn/dT (ppm/K)
Temperature (K)

• Key material properties (k, a, dn/dT) scale
  favorably at lower temperature in bulk single
  crystals
• Thermo-optic effects expected to be gt 30x smaller
  in 100 K YbYAG compared with 300 K NdYAG
• gt12x smaller than 300 K YbYAG (assuming equal
  optical efficiencies)

T. Y. Fan MIT Lincoln Laboratory
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Thermal Dissipation at Cold Tip

• About 9 of absorbed pump power dissipated in
  YbYAG by quantum defect
• Additional cold-tip thermal load from absorbed
  trapped fluorescence
• Cold-tip thermal load measured to be lt 0.3 J
  dissipated per J of laser output
• N2 Heat of Vaporization 200 J/g

T. Y. Fan MIT Lincoln Laboratory
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165-W Power Oscillator
Thin-Film Polarizers
YbYAG Crystal
LN2 Dewar
gt 165-W Output Power
Output Coupler
Pump Diodes

• Breadboard features
• YbYAG cryogenically cooled with LN2 cryostat
• Efficient end-pumping with high-brightness diode
  pump lasers
• Large beam radius to avoid optical damage

T. Y. Fan MIT Lincoln Laboratory
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165-W Results

• 165-W output power for 215-W incident pump power
• 85 slope efficiency, 76 incident power to
  output power efficiency
• M2 lt 1.1 measured at full power (automated
  scanning knife-edge)
• No measurable thermal lensing, thermal
  birefringence
• Results from unstable resonator using Gaussian
  variable reflectivity output coupler with 10
  effective output coupler

T. Y. Fan MIT Lincoln Laboratory
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Thermo-Optic Effects
295 K
80 K

• No observable thermal lensing with HeNe probe
• Negligible thermally induced birefringence
• Performance identical with and without
  intracavity polarizing Brewster plate

T. Y. Fan MIT Lincoln Laboratory
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255-W Single-Pass Amplifier
250-W Average Power Near-Field Beam Profile M2
1.1
Amplifier Performance

• 255-W generated by amplifying 110-W in a
  single-pass amplifier
• M2 1.1 measured from amplifier
• 54 optical-optical efficiency of single-pass
  amplifier
• Beam size 0.9-mm radius
• Low-risk approach to boost power

T. Y. Fan MIT Lincoln Laboratory
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300-W Power Oscillator
Output Coupler
LN2 Dewar
YbYAG Crystals
Near-Field Profile at 275 W
Polarizers
Polarization Multiplexing
Pump Diodes

• 308-W average power polarized
• 64 optical-optical efficiency
• M2 1.2 (wavefront sensor)
• gt 99 linearly polarized
• OC reflectivity 25, L 1 m, Near-flat-flat
  resonator
• Smaller volume, simplified design compared with
  single-pass amplifier

T. Y. Fan MIT Lincoln Laboratory
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Summary

• Results
• 308-W linearly polarized output power for 478-W
  incident pump
• 64 optical-optical efficiency, cw waveform, M2
  1.2
• Alternative single-pass amplifier demonstrated up
  to 255 W
• Negligible thermo-optic distortion, birefringence
• Thermo-optic material properties of YAG measured
  as a function of temperature

Near-Field Profile at 275 W
Cryogenic YbYAG is enabling for
high-average -flux and high-fluence ICS sources
T. Y. Fan MIT Lincoln Laboratory