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, Germany2 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-up Experimental 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.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 < 1.1Small 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] 3.6 12 11

σemission [10-20 cm2]

6 1.2 2.1

σabsoption [10-20 cm2]

1.8 3.1 0.8

τ [µs] 300 820 951Δλemission [nm] 1020-1035 1027-1039 1029

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.

M2 Xtal Xtal M3 M5 M6