Development of High Average Development of High Average Power Femtosecond Amplifiers Power Femtosecond Amplifiers with Ytterbium-doped crystals with Ytterbium-doped crystals Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with Amplitude Sytèmes
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Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with.
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Development of High Average Development of High Average
Power Femtosecond Amplifiers Power Femtosecond Amplifiers
with Ytterbium-doped crystalswith Ytterbium-doped crystals
Sandrine RICAUD
PhD supervisor: Frédéric DRUON
Thèse Cifre with Amplitude Sytèmes
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IntroductionIntroductionA femtosecond pulse or 10-15 second?
Pulses are Fourier limited if:
.t = 0,315
Pulses with t = 100 fs =12 nm centered at 1050 nm
Shorter pulses broader spectrum
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Hot topicsHot topics
• Diode-pumped solid-state laser
• High repetition rate, high energy
(high average power)
• Search for new materials, to generate ultra-short pulses ~ 100 fs
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Advantage of ytterbiumAdvantage of ytterbium
• Diode-pumped laser (980 nm)
• Large emission cross section– tens of nm for Yb3+
– < 1 nm for Nd3+
• Simple structure– No quenching even for closed
Yb3+ ions...
• Small quantum defect
Ideal candidate for diode-pumped
femtosecond laser
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ConclusionConclusion
- Diode-pumped room-temperature regenerative Yb:CaF2 amplifier operating at low and high repetition rate.
- Short pulses up to 1 kHz repetition rate (178 fs at 500 Hz).
- Maximum extracted energy : 1.6 mJ/0.7 mJ (before / after compression).
- Highest average power : 1.4 W/0.6 W (before / after compression).
- Optical efficiency ranging from 5 to 10%.S. Ricaud et al., "Short pulse and high repetition rate diode-pumped Yb:CaF2 regenerative amplifier" Opt. Lett. 35, 2415-2417 (July 2010)
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PerspectivesPerspectives
• Cooling crystals to cryogenic temperature
(better thermal and spectroscopic properties)S. Ricaud et al., “Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF2”, Opt. Lett. , vol. 35, p.3757 (2010)
S. Ricaud et al., “High-power diode-pumped cryogenically-cooled Yb:CaF2 laser with extremely low quantum defect”, submitted
• Thin-Disk technology
(better cooling, pump recycling)
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Thank you
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97 W !Absorption : - 74 W( saturated) without laser- Up to 150 W with laser
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Tunability curveTunability curve
Quantum defect 1.1% (992 nm)
Laser diode245 W @ 979 nm
Ø=400µm
Yb:CaF2
Prism2% OC
P
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Crystal choiceCrystal choice
Glass(amorphous)
Crystals with complex structure
Crystals with simple structure
Emission bandwidth
Thermal conductivity
Materials (W m-1 K-1)
Yb:YAG = 10
Yb:Verre = 0,8
(nm)
9
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Crystal choiceCrystal choice
Glass(amorphous)
Crystals with complex structure
Crystals with simple structure
Materials (W m-1 K-1)
Yb:YAG = 10
Yb:Verre = 0,8
Emission bandwidth
Thermal conductivity
Ideal crystal
(nm)
9
35
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ConclusionConclusion
• First laser operation of a singly doped Yb:CaF2 at a cryogenic temperature and high power level
• Promissing results at cryogenic temperature:– Efficiency up to 70%– Output power ~ 100W– Small signal gain: 3.1– Broad laser wavelength tunability– High gain at 992 nm
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OutlineOutline
• Material properties- Yb:CaF2 interest
- Advantages of cryogenic temperature
-Yb:CaF2 properties at 77K
• High power laser-Experimental setup-Cw regime results
• Conclusion
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Choix des matériauxChoix des matériaux
Cr4+ :fo
rste
rite
600 800 1000 1200 1400 1600 1800 2000
Cr3+ :L
iSAF
Cr4+ :Y
AG
Ti3+
:Sap
hir
Er3+
:ver
re
Tm3+
:ver
re
Yb3+
Nd3+
nm
• Pompage avec des diodes laser de puissance
-- 808 et 880 nm => ion dopant Néodyme
-- 940 et 980 nm => ion dopant Ytterbium
• Spectre d’émission large (lié à l’ion dopant et à la matrice)
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Yb:CaFYb:CaF22 background at room background at room temperaturetemperature
κ~6 W.m-1.K-1 2.7%-doped• ML oscillator: 99fs, 380mW• Regenerative amplifier:
215fs @1Hz, 17.3 mJ before compression
178fs @ 500Hz, 1.8mJ before compression• Multipass amplifier:
192fs @1Hz, 420mJ before compression
A. Lucca et al., “High-power tunable diode-pumped Yb3+:CaF2 laser ”, Opt. Lett., vol. 29, p.1879 (2004)J. Boudeile et al., “Thermal behaviour of ytterbium-doped fluorite crystals under high power pumping ”, Opt. Exp., vol. 16 (2008)F. Friebel et al., “Diode-pumped 99fs Yb:CaF2 oscillator”, Opt. Lett., vol. 34, p.1474 (2009) S. Ricaud et al., “Short-pulse and high-repetition-rate diode-pumped Yb:CaF2 regenerative amplifier”, Opt. Lett., vol. 35 (2010) M. Siebold et al., “Broad-band regenerative laser amplification in ytterbium-doped calcium fluoride (Yb:CaF2) ”, Ap. Phys. B 89 (2007)M. Siebold et al., “Terawatt diode-pumped Yb:CaF2 laser”, Opt. Lett., vol. 33, p.2770 (2008)
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Gain estimationGain estimation
Experimental small signal gain: Go=3.1
Inversion population estimated: β=0.4
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Watch out for the dopingWatch out for the doping
() 1
24ZNVm
32kB0
arctan 2
Vm4ZN
30
2kB
c ii
M i Mc iM i
i
2* R. Gaumé, et al. "A simple model for the prediction of thermal conductivity in pure and doped in saluting crystals," Appl. Phys. Let. 83, 1355-1357 (2003).
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Thermal propertiesThermal properties
G. A. Slack, "Thermal Conductivity of CaF2, MnF2, CoF2, and ZnF2 Crystals" Phys. Rev. 122, 1451–1461 (1961).
10 W/m/K @ 300K
68 W/m/K @ 77K
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Thermal propertiesThermal properties
* R. Gaumé, et al. "A simple model for the prediction of thermal conductivity in pure and doped in saluting crystals," Appl. Phys. Let. 83, 1355-1357 (2003).
using the Gaumé’s model [*] and assuming a sound velocity of 6000 m/s at 77 K