Ultrafast amplifiers

Transcription

1 ATTOFEL summer school 2011 Ultrafast amplifiers Uwe Morgner Institute of Quantum Optics, Leibniz Universität Hannover, Germany Centre for Quantum Engineering and Space-Time Research (QUEST), Hannover, Germany Laser Zentrum Hannover, Hannover, Germany

2 introduction Pulse energy mj µj amplifier MHzoscillator nj oscillator Up to 100 khz 1-10 MHz > 10 MHz Pulse repetition rate

3 Intensity = power per unit area Direct sunlight 1000 W/m 2 = 0.1 W/cm 2 Hot plate 3 W/cm 2 Sun + lens (burning glas) 1000 W/cm 2 Laserpointer on the retina: 1000 W/cm 2 Welding apparatus W/cm 2 Laser (cw 10W) + lens: W/cm 2 =10 9 W/cm 2 Laser (pulsed) + lens: W/cm 2 =10 18 W/cm 2

4 Field strength forces on free electrons E(V/cm) = 27.4 I(W/cm W/cm Lorentz force: r F = m & r e 9 2 ) V/cm r r r = e( E + v B) E r t Ponderomotive energy: U P = m r & e 2 W/cm e E = 2 4meω0 60 ev v=r

5 Laser pulse intensities Laser intensity - Intensität (W/cm (W/cm 2 ) 2 ) nuclear optics relativistic optics electron bond Quelle: Mourou Jahr year

6 Chirped Pulse Amplification

7 Section I cavity dumping

8 Dynamic output coupling SAM Pump diode Crystal TFP HR Ē Dispersive mirrors Output coupling Pockels-cell cw-mode-locking cavity dumping regenerative amplification T rep output T rep output T rep output coupler dumping depth seed 100% time time

9 Yb:KYW oscillator Diode-pumped Yb:KY(WO4)2 oscillator with electro-optical cavity-dumping

10 Experimental set-up Yb:KYW 2 x nm Cavity-dumping G. Palmer et al. OE 18, (2010)

11 Experimental results Intensity Time Maximum dumping efficiency: 67 % Pulse energy (@ 1 MHz): 7 µj Pulse duration: 450 fs G. Palmer et al. OE 18, (2010)

12 Take home from section I Cavity dumping bridges the gap between oscillators and amplifier systems Production of µj / MHz pulses from a compact source

13 Section II regenerative amplifier

14 Dynamic output coupling SAM Pump diode Crystal TFP HR Ē Dispersive mirrors Output coupling Pockels-cell cw-mode-locking cavity dumping regenerative amplification T rep output T rep output T rep output coupler dumping depth seed 100% time time

15 Regenerative Yb:KYW amplifier U. Bünting, OE 17, 8046 (2009)

16 Combined gain spectra 1025 nm 1040 nm Absorption-/ Emission cros section (10-12 cm 2 ) wavelength (nm) Pujol et al, PRB 65, (2002)

17 185 fs 0.5 mj 20 khz U. Bünting, OE 17, 8046 (2009)

18 Thin disk regenerative amplifiers pulse energy (µj) Yb:YAG Yb:KYW repetition rate (khz) Cavity dumping!

19 Take home from section II Small single pass gain / long upper state lifetime regenerative Amplifier Regenerative amplifiers allow for increasing the pulse energy by reducing the repetition rate Combined gain spectra lead to short pulses

20 Section III fiber amplifier

21 Fiber amplifier

22 CPA with chirped fiber gratings Appl. Phys. Lett. 66 (1995)

23 Fiber CPA system Summary of all limiting effects in fiber CPA system J. Limpert et al, IEEE JSTQE 12 (2006)

24 Fiber amplifier results Highest avarage power: 830 W (78 MHz, 640 fs, 12 MW) [1] Highest peak power: 3.2 GW [2] Highest pulse energy: 3 mj (5kHz, 15 W, 480 fs (dechirped)) [2] [2] [1] Eidam et al., OL 35 (2010) [2] Eidam et al., OE19 (2010)

25 Take home from section II Ultrafast fiber amplifier approaching the kw average power / mj pulse energy Fiber amplifiers outperform many solid state systems especially in the high-rep rate regime

26 Section IV multipass amplifier

27 Innoslab

28 Innoslab power amplifier (MOPA) 1,1 kw 640 fs 20 MHz 55 µj Russbueldt et al. OL 35, 4169 (2010)

29 Multipass amplifier A. Krüger, spie s oe magazine (2002)

30 Typical commercial CPA laser system 776 nm 3 khz 1,5 mj 35 fs 776 nm 80 MHz 6 nj 14 fs

31 Ultrashort pulse generation Spectral broadening (hollow core fiber 1, filamentation 2 ) Recompression [1] M. Nisoli, et al., Opt. Lett. 22, 522 (1997) [2] C. P. Hauri et al., Appl. Phys. 33 B 79, 673 (2004)

32 Nonlinear pulse propagation II Self-phase modulation [1] time time [2] Bergmann Schaefer, Optik, Walter de Gruyter. (1993) 34

33 Nonlinear pulse propagation I Self-focusing Phase fronts Transversal beam profile nonlinear medium

34 Filamentation Self-guiding model self-focusing Balancing effects: Kerr self-focusing Nonlinear absorption free electron plasma de-focusing ~ 20 cm 2 λ = Pkr πn0 2 n 2

35 D. S. Steingrube et al., OE 17, (2009) Few-cycle pulses from filamentation Spectrum Reconstructed pulse duration

36 Filamentation for strong field physics Filament as compressor: A. Zair et al. Opt. Exp. 15, 5394 (2007) Eckle et al. Nat. Phys. 4, 565 (2008) J.-H. Lee et al. Appl. Phys. B 96, 287 (2009) Mansten et al. PRL (2009) Filament as generating medium for HHG: Couairon et al. J. Mod. Opt. 53, 75 (2006) C.P. Hauri et al. JTuE5 OSA/CLEO (2006) Filament as compressor AND generating medium?

37 Filament as compressor AND generating medium Generating HHG directly out of a filament No dispersive reshaping of the pulse Generation of isolated attosecond pulses?

38 M. B. Gaarde, A. Couairon, PRL 103, (2009) HHG within a filament Theoretical prediction: Intensity spikes at certain positons inside the filament

39 M. B. Gaarde, A. Couairon, PRL 103, (2009). 41 Spatio-temporal evolution

40 Experimental setup - HHG 42

41 43 Experimental setup - HHG 1000mbar mbar

42 D S Steingrube et al, New J. Phys (2011) 44 Comparison experiment and theory Experiment (1 bar) Theory (1 atm) Theoretical model : (M.B. Gaarde, A. Couairon) Real field propagation Equation Strong field approximation Ionization rates (Keldysh, PPT, ADK, Ilkov et al.) Experimental observation of intensity spikes

43 Take home from section IV Multipass amplifiers (Ti:sapphire) are the current workhorses for mj fs pulse generation With external spectral broadening/pulse compression few-cycle pulses are generated A novel scheme allows for broadening/compression and HHG in a single truncated filament

44 Section V parametric amplifier

45 Parametric amplification ω p ω s Conservation of energy: ω p ω s χ (2) ω i Conservation of momentum: ω s ω p χ (2) ω i ω p ω s ω p ω s ω i λ p = 515 nm λ s = 800 nm λ i = 1450 nm

46 Noncollinear Amplification (NOPA) OPA-Efficiency Optical frequency (THz) 48

47 Difference between OPA and NOPA process Collinear geometry: Signal and idler: different group velocities pulse broadening and bandwidth reduction Non-collinear geometry: Pulses stay effectively overlapped Phase matching condition: Cerullo et al., Rev. Sci. Instrum. 74, 1 (2003)

48 High rep rate parametric amplifier Existing OPCPA systems at 800 nm: High repetition rate concepts above 1 MHz: [1]: white light generation in YAG: High energetic systems between 1 and 100 khz: 1 MHz, 9.6 fs, 420 nj [3]: Ti:sa oscillator + Yb fiber amplifier chain: [2]: white light generation in sapphire: 98 khz, 68 µj, 8 fs 2 MHz, 14 fs, 860 nj [4]: Ti:sa oscillator + Yb fiber amplifier chain: 30 khz, 100 µj, <5 fs [1] Emons et al, OE 18 (10) [2] Schriever et al, OL 33 (08) [3] Rothhardt et al, OE 18 (10) [4] Hädrich et al, OL 36 (11)

49 Schematic setup

50 Double-stage parametric amplifier SPIDER 3.3 µj khz FL- pulse duration: 5.2 fs Peak power: ~ 260 MW

51 Take home from section V Parametric amplifiers behind Yb-solid state technology are the future! Based on high energy solid-state femtosecond pump lasers they can produce high energy few-cycle pulses in many different wavelength regions

52 Thank you for your attention! special thanks to: Milo Kovacev, Emilia Schulze, Daniel Steingrube, Guido Palmer, Moritz Emons, Martin Siegel, Thomas Binhammer, Stefan Rausch, Anne Harth, Marcel Schultze