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Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals

Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals. Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with Amplitude Sytèmes . Introduction. A femtosecond pulse or 10 -15 second ?. Pulses are Fourier limited if:  .  t = 0,315

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Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals

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  1. Development of High Average Power FemtosecondAmplifierswith Ytterbium-dopedcrystals Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with Amplitude Sytèmes

  2. Introduction A 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

  3. Hot 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

  4. Advantage 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

  5. Ytterbium-dopedmaterials Collaborations: CIMAP LCMCP Sc2O3 Y2O3 YAG Thermal conductivity (W/m/K) CaF2 GGG CALGO SrF2 LSO YVO4 SFAP YSO KGW YCOB glass BOYS KYW SYS GdCOB Emission bandwidth (nm) For High power For Short pulses

  6. Ca Ca F F Ca F F Yb3+:CaF2 Ca Ca CaF2 interest • Exception to the rule: good spectroscopic and thermal properties • Well-known crystal (undoped), good growth control • Cubic structure (isotrop) Yb(2.6%):CaF2 grown by the Bridgman process

  7. Chirped Pulse Amplification D. Strickland and G. Mourou, "Compression of Amplified Chirped Optical Pulses," Optics Comm. 56, 219 (1985).

  8. Chirped Pulse Amplification Yb:CALGO 15 nm, <100 fs 27 MHz Yb:CaF2 regenerative amplifier 100-10 kHz D. Strickland and G. Mourou, "Compression of Amplified Chirped Optical Pulses," Optics Comm. 56, 219 (1985).

  9. Yb:CALGOoscillator 27 MHz, sub 100-fs, 15 nm bandwidth centered at 1043 nm

  10. Yb:CaF2regenerative amplifier

  11. Yb:CaF2 amplifier • Maximum energy plateau up to 300 Hz : 1.6 mJ / 700 µJ (uncompressed / compressed) • Higher repetition rate : 10 kHz 1.4W / 0.6W • (uncompressed / compressed) Beam profile : Gaussian shape with M2 < 1.1

  12. SHG FROG trace at 500 Hz At 500 Hz repetition rate : - pulse duration : 178 fs - pulse energy : 1.4 mJ before compression 620 µJ after compression - optical-to-optical efficiency : 4.5 % 178 fs 8.5 nm Measured Retrieved 15 nm

  13. Conclusion • 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)

  14. Perspectives • 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)

  15. Thank you

  16. Spectroscopy V. Petit et al (Appl. Phys. B, 2004) Ca2+ Yb3+ Charge compensation Crystalline reorganization Clusters Broad absorption and fluorescence spectra • Diode pumping • Tunability / ultrashort pulses • Long emission lifetime (2.4 ms) Hexameric cluster

  17. Thermal properties Y2O3 Favorable directions YAG CaF2 SrF2 CALGO LSO YVO4 KGW YSO BOYS SYS S-FAP glass

  18. Regenerative Amplifier Grating compressor 1600 l/mm M4 Diode-pumped CPA laser chain FR PC Fs-oscillator FWHM bandwidth: 15 nm 27 MHz Grating stretcher 1600 l/mm 260 ps M2 M3 λ/2 TFP TFP Mirror R=300mm M1 TFP: Thin-Film Polarizer FR: Faraday Rotator PC: Pockels Cell Laser diode 16 W @ 980 nm Ø=200µm Mirror R=300mm 50 mm triplets Dichroic mirror Yb:XxF2 Yb:CaF2 : 2.6-%-doped 5-mm-long Yb:SrF2 : 2.9-%-doped 4-mm-long

  19. Advantages of cryogenictemperature • Lower laser levels become less thermally populated: lower laser threshold, higher efficiency • Better thermal properties (thermal conductivity, coefficient of thermal expansion) • Emission and absorption cross sections increase: higher gain but more structured Higher average power system

  20. Spectroscopicpropertiesat 77K Saturation intensity: 17 kW/cm2compared to 33 kW/cm2 at room temperature S. Ricaud et al., “Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF2”, Opt. Lett. , vol. 35, p.3757 (2010)

  21. Interest of cryogeny 68 W/m/K @ 77K 10 W/m/K @ 300K G. A. Slack, "Thermal Conductivity of CaF2, MnF2, CoF2, and ZnF2 Crystals" Phys. Rev. 122, 1451–1461 (1961).

  22. Experimental setup OC: Output Coupler P: Powermeter

  23. Cwregimeresults OC: 10% Maximal incident pump power: 212W 97 W ! Absorption : - 74 W( saturated) without laser - Up to 150 W with laser • High pump power: 245W • High efficiency > 60% • Good beam quality maintained • Measured thermo-optic coefficient around -11 x10-6 K-1 (theory -3.1 x10-6 K-1 ) • Small signal gain estimation: 3.1

  24. Tunability curve Quantum defect 1.1% (992 nm) Yb:CaF2 Laser diode 245 W @ 979 nm Ø=400µm Prism 2% OC P

  25. Crystal choice Glass (amorphous) Crystals with complex structure Crystals with simple structure (W m-1 K-1) Materials l (nm) Yb:YAG = 10 9 Yb:Verre 35 = 0,8

  26. Crystal choice Glass (amorphous) Crystals with complex structure Crystals with simple structure Ideal crystal (W m-1 K-1) Materials l (nm) Yb:YAG = 10 9 Yb:Verre 35 = 0,8

  27. Conclusion • 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

  28. Outline • Materialproperties -Yb:CaF2interest - Advantages of cryogenictemperature • Yb:CaF2propertiesat 77K • High power laser • Experimental setup • Cwregimeresults • Conclusion

  29. 600 800 1000 1200 1400 1600 1800 2000 Choix des matériaux • Spectre d’émission large (lié à l’ion dopant et à la matrice) Nd3+ Cr4+:YAG Cr4+:forsterite Ti3+:Saphir Cr3+:LiSAF Tm3+:verre Yb3+ Er3+:verre nm • Pompage avec des diodes laser de puissance • -- 808 et 880 nm => ion dopantNéodyme • -- 940 et 980 nm => ion dopantYtterbium

  30. Yb:CaF2 background at room temperature • Laser wavelength tunability: 50nm • Thermal behaviour: κ~9.7 W.m-1.K-1 undoped, 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)

  31. Gain estimation Experimental small signal gain: Go=3.1 Inversion population estimated: β=0.4

  32. Watch out for the doping * 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).

  33. Thermal properties 68 W/m/K @ 77K 10 W/m/K @ 300K G. A. Slack, "Thermal Conductivity of CaF2, MnF2, CoF2, and ZnF2 Crystals" Phys. Rev. 122, 1451–1461 (1961).

  34. Thermal properties using the Gaumé’s model [*] and assuming a sound velocity of 6000 m/s at 77 K * 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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