57-mj multi-hz multipass laser amplifier based on yb:caf2...

57-mJ multi-Hz multipass laser amplifier

based on Yb:CaF2 Crystals

JNCO – Cherbourg – June 11th 2013

[email protected]

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

mailto:[email protected]

mailto:[email protected]

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


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


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


1030-nm CPA chain


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%


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


Outline





• Conclusion


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


Reinjection

980nm, 400W, 20 Hz,

2,25 ms, 1.8 J, 36 W

Output

Npass = 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

Output

53mJ,100Hz

3.1nm, 1030nm λ/2

…~pJ @1030nm from the


Reinjection

980nm, 400W, 20 Hz,

2,25 ms, 1.8 J, 36 W

x 2 Total Npasses = 16

Npasses =8


Outline





• Conclusion


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


• 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


Beam Quality

•30 min running @ 50 mJ

•The pointing stability<20μrad

Output

Excellent beam

quality

M2 ~ 1.1


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


Spectrum

•∆λ=3.1 nm, FTL~600 fs (∆t~1.5 ns) / Injection spectrum limited


Outline





• Conclusion


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


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


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


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



Pu

mp

[a.u

]

Temporal delay between thermal lens and heat load

The thermal load follows the fluo and not the pump !



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


Outline





• Conclusion


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.


Merci pour votre attention

57-mj multi-hz multipass laser amplifier based on yb:caf2...

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