1. Formatvorlage des Untertitelmasters durch Klicken bearbeiten 1/26/15 1 kHz, multi-mJ Yb:KYW bulk regenerative amplifier 1 Ultrafast Optics and X-Ray Division, Center for Free-Electron Laser Science / DESY, Notkestrasse 85, 22607 Hamburg, Germany 2 Department of Physics and the Hamburg Centre for Ultrafast Imaging, University of Hamburg Luruper Chaussee 149, D-22761 Hamburg, Germany 3 Department of Electrical Engineering and Computer Science, MIT-RLE, Cambridge, Massachusetts 02139, USA Anne-Laure Calendron1,2, Huseyin Cankaya1,2, Franz Kärtner1,2,3 Characteristics: Cavity: - Dual-crystal resonator similar to Ref. [1] - Insensitive to variation of thermal lenses for fth = 280 – 800 nm Crystals: - 3 mm, 2%-Yb:KYW crystals - ng – cut, lasing on nm Pump: - Fiber coupled laser diode NA=0.15, MFD = 200 µm - Wavelength λ = 981 nm - Maximal pump power PP = 120 W Motivation Experimental set-upExperimental results References Conclusions High-energy lasers are sought for Pumping of Optical Parametric (Chirped Pulse) Amplifiers Micro-machining Surgery Aim at >5mJ, low repetition rate (~kHz) Design criteria: Distribution of thermal load Minimization of non-linearities  Solution: Regenerative amplifier with short crystals and increased pump spots Fig. 1: Layout of the resonator. [1] A.-L. Calendron, ”Dual-crystal Yb:CALGO high power laser and regenerative amplifier”, Opt. Express, (2013) [2] Eksma Website: http://www.eksmaoptics.comhttp://www.eksmaoptics.com [3] R. Peters, C. Kränkel, S. T. Fredrich-Thornton, K. Beil, K. Petermann, G. Huber, O. H. Heckl, C. R. E. Baer, C. J. Saraceno, T. Südmeyer, and U. Keller, “Thermal analysis and efficient high power continuous-wave and mode-locked thin disk laser operation of Yb-doped sesquioxides” Appl Phys B 102, 509 (2011) [4] R. Peters, C. Kränkel, K. Petermann, and G. Huber, “Broadly tunable high-power Yb:Lu2O3 thin disk laser with 80% slope efficiency”, Opt. Express 15, 7075 (2007) [5] Roditi Website: http://www.roditi.com/Laser/Yb_Yag.html Fig. 3: Variation of the beam size in the crystal versus thermal lens. Fig. 5: Tuning curve with beam quality M2 < 1.1 Small signal absorption: 60%. Fig. 4: Slope efficiency. Free running laser output wavelength: 1031 nm Fig. 6: Extraction in cavity-dumped operation for 850 ns extraction time, at 1 kHz and for quasi-CW pumping. Pulse duration (20 ns) corresponds to cavity round-trip. Limitation: pump power. - Demonstration of a high power laser head with two 2% doped Yb:KYW crystals - In CW operation: nearly 20 W output power from 2 crystals pumped with 123 W – free running wavelength: 1031 nm - In cavity dumped operation, extraction up to 5.5 mJ @ 1 kHz - Seeded with 0.6 nJ energy, 6.5 mJ extracted @ 1 kHz with 3.6 nm broad pulses supporting < 1 ps - Outlook: - White-light generation with compressed pulses - Scaling up to higher energies and higher average powers Seeded operation: Continuous-wave operation: Yb:KYW[2]Yb:Lu2O3[3,4]Yb:YAG @300K[5] κundoped [W/m/K]3.61211 σemission [10-20 cm2] 61.22.1 σabsoption [10-20 cm2] 1.83.10.8 τ [µs]300820951 Δλemission [nm]1020-10351027-10391029 Tab. 1: Material properties. Fig. 7: Spectra of the seed, in cavity-dumped and seeded operations. The gain narrowing after the regenerative amplifier corresponds to the overlap of seed and CD spectra. 19.4 W 1030.5 nm Fig. 8: Long-term measurement of the regenerative amplifier. RMS < 1% S Fig. 2: Variation of the waist at “S“ with the thermal lens. Constant spot sizes in the rest of the cavity. Of importance for: - Output beam: same parameters for thermal lenses between 280 mm and 800 mm. - Pumping in QCW or CW regimes possible Fig. 9: Pointing stability measurement of the regenerative amplifier. M2Xtal M3M5M6