57-mJ multi-Hz multipass laser amplifier
based on Yb:CaF2 Crystals
JNCO – Cherbourg – June 11th 2013
http://www.lcf.institutoptique.fr/lcf-en
Florence Friebel*1, Alain Pellegrina2, Dimitris N.Papadopoulos2, Patrice Camy3, Jean-Louis Doualan3, Richard Moncorge3, Patrick Georges1, Frédéric Druon1
1. Laboratoire Charles Fabry, Institut d'Optique (LCF), CNRS, Univ. Paris Sud, Palaiseau, France
2. Laboratoire d’Utilisation des Lasers Intenses (LULI), Ecole Polytechnique, Palaiseau, France
3. Centre de Recherche sur les Ions, les Matériaux et la Photonique(CIMAP), Caen, France
2 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 2
Outline
• Cilex-Apollon project
• High-energy Yb:CaF2 multipass amplifiers
• High energy multipass amplifier at 20 Hz
• Thermal survey of crystals at 100Hz
• Conclusion
3 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 3
Apollon 10 PW laser
Amplification Stages
based on Ti:Sa 300 J @ 800 nm
Compressor 15 fs, 150 J
@ 800 nm,
1pulse/mn
Pump Laser Nd:glass
0.8 KJ, 1pulse/mn
Front End OPCPA based
10fs,100mJ, >20Hz
LABORATOIRE CHARLES FABRY
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The Apollon front end source
Nonlinear pulse
compression/cleaning
<10 fs, CR>1012
Ti:Sapphire CPA
25 fs, 1.5 mJ
Signal source @ 800 nm
Diode pumped high energy amplifiers
based on Ytterbium doped crystals
J range@ 515 nm by SHG
>20 Hz
Pump source @ 515 nm
Ti:Sapphire oscillator
< 7 fs
1030 nm
800 nm OPCPA Multi-stages
based on BBO
crystals
< “10 fs”
stretched to > 1 ns
100 mJ, >20 Hz
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1030-nm CPA chain
Ti:Sapphire oscillator
YDFA
Stretcher, 0.5ns/nm
Yb:KYW regen.
2mJ
MP2
Yb:CaF2
~200 mJ, >20 Hz
SHG
>50%
MP1
CaF2
>20 mJ, >20 Hz
ns-OPCPA
J,~1.5 ns
>20 Hz
@515 nm
Nanosecond Stage
…to OPCPA signal
@800nm
BS
MP3
Yb:CaF2
1030 nm injection
~4 pJ@1030nm
Co
mp
r. ~
16 p
s ps-OPCPA
>80 mJ, ~12 ps
100 Hz
@515 nm
Picosecond Stage
Yb:YAG regen (M.B.I.)
>200 mJ
100Hz
SHG
~60%
6 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 6
Material for high-energy amplifiers
Yb:CaF2
• Large Bandwidth
(<100fs)
• Good thermal
conductivity(~YAG)
• Long fluorescence
lifetime (2.4 ms)
• New revival of an
old Crystal
W. Humphreys, Astrophysical Journal, 266 (1904)
A. Lucca, et al. Opt. Lett. 1879 (2004)
A. Lucca, et al. Opt. Lett. 2767 (2004)
M. Siebold, et al. Opt. Lett., 2770 (2008).
F. Friebel, et al. Opt. Lett.,1474–1476 (2009)
F. Druon, et al. IEEE Photonics Journal Vol. 3, 2, 268 (2011)
F. Druon, et al. Opt. Material Exp. 1, 489 (2011)
− Low Emission cross section
− Low gain
7 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 7
Outline
• Cilex-Apollon project
• High-energy Yb:CaF2 multipass amplifiers
• High energy multipass amplifier at 20 Hz
• Thermal survey of crystals at 100Hz
• Conclusion
8 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 8
Experimental setup
1:3.75
30cm
115cm
ROC: 2m Yb:CaF2
2mm,2,2%
S-pulse Yb:KYW
regenerative amp.
1kHz, 2mJ,
3-5nm,1030nm
λ/2
…~pJ @1030nm from the
Ti:Sapphire oscillator
Reinjection
980nm, 400W, 20 Hz,
2,25 ms, 1.8 J, 36 W
Output
Npass = 8
9 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 9
Experimental setup
1:3.75
30cm
115cm
ROC: 2m Yb:CaF2
2mm,2,2%
S-pulse Yb:KYW
regenerative amp.
1kHz, 2mJ,
3-5nm,1030nm
Output
53mJ,100Hz
3.1nm, 1030nm λ/2
…~pJ @1030nm from the
Ti:Sapphire oscillator
Reinjection
980nm, 400W, 20 Hz,
2,25 ms, 1.8 J, 36 W
x 2 Total Npasses = 16
Npasses =8
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Outline
• Cilex-Apollon project
• High-energy Yb:CaF2 multipass amplifiers
• High energy multipass amplifier at 20 Hz
• Thermal survey of crystals at 100Hz
• Conclusion
11 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 11
Simulation-Expected output
E o
ut (J
)
E s
tore
d (
J)
Population inversion level
in the CaF2 Crystal
Number of passes
• Stored energy estimation: Esto~150mJ (Ep~1.2J,
Δtpump~ 2,25 ms)
• With: Np.max = 15 Eout,theory > 60 mJ
980nm, 400W, 20 Hz,
2,25 ms, 1.8 J, 36 W
Stored energy & extraction efficiency estimation
Operating point
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• Eout~57,4 mJ @ 20 Hz , Np~15,
Einput ~1,1mJ Gain is 32
Results
Eo
ut /
mJ
Einjection / mJ
EFirst pass / mJ
Eout / mJ
57,4 mJ
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Beam Quality
•30 min running @ 50 mJ
•The pointing stability<20μrad
Output
Excellent beam
quality
M2 ~ 1.1
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Temperature Profile
Local surface temperature profile at maximum pumping
Image By Thermal Camera (7.5 – 13 µm)
Surface of CaF2-Crystal in Mount (right)
(Below)
Heat conduction on the crystal for pumping
from 0 - 400 W in three steps
• max. surface temperature 28 ºC (max.
increase of +15 ºC)
30
28
26
24
22
20
18
16
14
1) 28 ºC
2) 23 ºC
3) 15 ºC
Trace 1)
Trace 2)
Trace 3)
Te
mp
era
ture
/
Cº
AR-coating HR – coating
heat
Active mirror
Heat
spre
ader
Te
mp
era
ture
/
Cº
30
28
26
24
22
20
18
16
14
Time/ min
0 2 4 6 8
Good thermal management
Low heating
1) 28 ºC
2) 23 ºC
3) 15 ºC
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Spectrum
•∆λ=3.1 nm, FTL~600 fs (∆t~1.5 ns) / Injection spectrum limited
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Outline
• Cilex-Apollon project
• High-energy Yb:CaF2 multipass amplifiers
• High energy multipass amplifier at 20 Hz
• Thermal survey of crystals at 100Hz
• Conclusion
17 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 17
Thermal Profile
Local surface temperature profile at maximum pumping
Image By Thermal Camera (7.5 – 13 µm)
Surface of CaF2-Crystal in Mount (right)
(Below)
Heat conduction on the crystal for pumping
at 400 W
• max. surface temperature 28 ºC (max.
increase of +15 ºC)
30
28
26
24
22
20
18
16
14
Te
mp
era
ture
/
Cº
Trace across
diameter of crystal
including the
central
heating part
Cooling very efficient
Using the active mirror configuration - from the backside
Te
mp
era
ture
/
Cº
30
25
20
18
16
14
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Thermal lens measurement
Dio
ptr
ic P
ow
er
[ m
-1]
Incident pump power [W]
Thermal lens 100 Hz
Thermal lens dependency on pump power
The thermal lens is
POSITIVE
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Thermal lens: Positive ?
BUT
Crystal in active mirror configuration
AR-coating
(thin= softer)
HR – coating
(thick= harder)
Add an asymetric
mechanical distortions
heat
Yb:CaF2
Even with thermo-
optic coefficient
cCaF2 < 0
Our hypothesis
« Bilame » effect
20 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 20
Thermal lens: Dynamics
Time / ms
Dio
ptr
ic p
ow
er
vari
ati
on
[%
]
Pu
mp
[a.u
]
Thermal lens
Theoretical current
Fluorescence
Pump
Measurement of the instantaneous thermal lens
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Thermal lens: Dynamics
Pu
mp
[a.u
]
Temporal delay between thermal lens and heat load
The thermal load follows the fluo and not the pump !
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Thermal lens: Dynamics
View from the energetic scheme
Pump
We have to wait for the
fluorescence before the
heating Fluo
Temporal delay between thermal lens and heat load
Non-radiative
deexcitation = HEAT
Quasi exclusive heat source
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Outline
• Cilex-Apollon project
• High-energy Yb:CaF2 multipass amplifiers
• High energy multipass amplifier at 20 Hz
• Thermal survey of crystals at 100Hz
• Conclusion
24 JNCO 2013 – M12 http://www.lcf.institutoptique.fr/lcf-en 24
Conclusion
• High energy multipass amplifier Eout = 57 mJ
• Repetition Rate 20 Hz
• Excellent beam quality M2 ~ 1.1, with 16 Passes
• The crystals handle 100 Hz heat load
• Positive thermal lens : active mirror≠brewster crystal
• Thermal lens dynamic linked to fluorescence shape
Current stability issues:
management of the fluorescence irradiation that
could heat the closest mounts to the crystal =>
air turbulences.
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Merci pour votre attention