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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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Presentation on theme: "Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with."— Presentation transcript:

1 Development of High Average Power Femtosecond Amplifiers with Ytterbium- doped crystals Sandrine RICAUD PhD supervisor: Frédéric DRUON Thèse Cifre with Amplitude Sytèmes

2 2 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 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 3 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 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 4 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 4 Advantage of ytterbium Diode-pumped laser (980 nm) Large emission cross section – tens of nm for Yb 3+ – < 1 nm for Nd 3 + Simple structure –No quenching even for closed Yb 3+ ions... Small quantum defect Ideal candidate for diode-pumped femtosecond laser

5 5 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 5 Ytterbium-doped materials Y2O3Y2O3 YAG SFAP KGW LSOYVO4 YSO glass BOYS SYS CaF 2 SrF 2 CALGO YCOB Sc 2 O 3 GdCOB KYW GGG Thermal conductivity (W/m/K) Emission bandwidth (nm) For High power For Short pulses Collaborations: CIMAP LCMCP

6 6 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 6 CaF 2 interest Exception to the rule: good spectroscopic and thermal properties Well-known crystal (undoped), good growth control Cubic structure (isotrop) Yb(2.6%):CaF 2 grown by the Bridgman process Yb 3+ :CaF 2 Ca F Ca Ca F F F Ca Ca

7 7 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 7 Chirped Pulse Amplification D. Strickland and G. Mourou, "Compression of Amplified Chirped Optical Pulses," Optics Comm. 56, 219 (1985).

8 8 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 8 Chirped Pulse Amplification Yb:CALGO 15 nm, <100 fs 27 MHz Yb:CaF 2 regenerative amplifier 100-10 kHz D. Strickland and G. Mourou, "Compression of Amplified Chirped Optical Pulses," Optics Comm. 56, 219 (1985).

9 9 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 9 Yb:CALGO oscillator 27 MHz, sub 100-fs, 15 nm bandwidth centered at 1043 nm

10 10 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 10 Yb:CaF 2 regenerative amplifier

11 11 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 11 Yb:CaF 2 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 M 2 < 1.1

12 12 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 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 % Measured Retrieved 178 fs 8.5 nm 15 nm

13 13 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 13 Conclusion - Diode-pumped room-temperature regenerative Yb:CaF 2 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:CaF 2 regenerative amplifier" Opt. Lett. 35, 2415-2417 (July 2010)

14 14 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 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:CaF 2 laser with extremely low quantum defect, submitted Thin-Disk technology (better cooling, pump recycling)

15 15 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 15 Thank you

16 16 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 16Spectroscopy Broad absorption and fluorescence spectra Clusters Crystalline reorganization Charge compensation Yb 3+ Ca 2+ Hexameric cluster V. Petit et al (Appl. Phys. B, 2004) Diode pumping Tunability / ultrashort pulses Long emission lifetime (2.4 ms)

17 17 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 17 Thermal properties S-FAP YAG Y2O3Y2O3 LSO KGW glass YVO 4 YSO BOYS SrF 2 CaF 2 CALGO SYS Favorable directions Undoped crystal~ 2.7%-Yb-doped crystal Thermal conductivity (W.m -1.K -1 ) 9.76 Thermo-optic coefficient (10 -6 K - 1 ) - 17.8- 11.3

18 18 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 18 Regenerative Amplifier Diode-pumped CPA laser chain M2 Laser diode 16 W @ 980 nm Ø=200µm Mirror R=300mm Dichroic mirror 50 mm triplets Mirror R=300mm PC TFP M1 Grating stretcher 1600 l/mm 260 ps Fs-oscillator FWHM bandwidth: 15 nm 27 MHz FR TFP M4 M3 λ/2 Grating compressor 1600 l/mm TFP: Thin-Film Polarizer FR: Faraday Rotator PC: Pockels Cell Yb:CaF 2 : 2.6-%-doped 5-mm-long Yb:SrF 2 : 2.9-%-doped 4-mm-long Yb:XxF 2

19 19 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 19 Advantages of cryogenic temperature 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 20 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 20 Spectroscopic properties at 77K S. Ricaud et al., Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF2, Opt. Lett., vol. 35, p.3757 (2010) Saturation intensity: 17 kW/cm 2 compared to 33 kW/cm 2 at room temperature

21 21 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 21 Interest of cryogeny 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

22 22 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 22 Experimental setup OC: Output Coupler P: Powermeter

23 23 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 23 Cw regime results 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 OC: 10% Maximal incident pump power: 212W 97 W ! Absorption : - 74 W( saturated) without laser - Up to 150 W with laser

24 24 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 24 Tunability curve Quantum defect 1.1% (992 nm) Laser diode 245 W @ 979 nm Ø=400µm Yb:CaF 2 Prism 2% OC P

25 25 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 25 Crystal 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 35

26 26 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 26 Crystal 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

27 27 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 27 Conclusion First laser operation of a singly doped Yb:CaF 2 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 28 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 28 Outline Material properties - Yb:CaF 2 interest - Advantages of cryogenic temperature -Yb:CaF 2 properties at 77K High power laser -Experimental setup -Cw regime results Conclusion

29 29 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 29 Choix des matériaux Cr 4+ :forsterite 600800100012001400160018002000 Cr 3+ :LiSAF Cr 4+ :YAG Ti 3+ :Saphir Er 3+ :verre Tm 3+ :verre Yb 3+ Nd 3+ nm Pompage avec des diodes laser de puissance -- 808 et 880 nm => ion dopant Néodyme -- 940 et 980 nm => ion dopant Ytterbium Spectre démission large (lié à lion dopant et à la matrice)

30 30 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 30 Yb:CaF 2 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 Yb 3+ :CaF 2 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:CaF 2 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:CaF 2 laser, Opt. Lett., vol. 33, p.2770 (2008)

31 31 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 31 Gain estimation Experimental small signal gain: G o =3.1 Inversion population estimated: β=0.4

32 32 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 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 33 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 33

34 34 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 34 Thermal 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

35 35 Journées de lEDOM 7-8 mars 2011 www.elsa-laser.u-psud.fr/ www.elsa-laser.u-psud.fr/ 35 Thermal 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 Gaumés model [*] and assuming a sound velocity of 6000 m/s at 77 K


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