1. SOUTHAMPTON High Average Power, High Energy, Femto-second Fiber Chirped Pulse Amplification System F. He, J. H. V. Price, A. Malinowski, A. Piper, M. Ibsen, D. J. Richardson Optoelectronics Research Centre University of Southampton, Southampton, UK J. W. Dawson, C. W. Siders, J. A. Britten, C. P. J. Barty Lawrence Livermore National Laboratory, 700 East Avenue, Livermore, USA

2. SOUTHAMPTON Outline nBackground and motivation nExperimental setup  Fiber oscillator  Chirped Fiber Bragg Grating (CFBG)  Large Mode Area (LMA) fiber  Modelling tools for bandwidth optimization  Dielectric grating compressor nExperimental results nConclusion and future work

3. SOUTHAMPTON Background and Motivation nFiber Chirped Pulse Amplification (CPA) system with high- quality, high-energy femto-second pulses, at high average power.  Applications: industrial materials processing, etc.  Fiber systems: high gain, compact and robust, less thermo-optical problems at high power.  Limitations: nonlinear effects nCompact  Fiber oscillator and stretcher nThe key for achieving high P ave + E P ave + E  Dielectric grating

4. SOUTHAMPTON Experimental setup Novel technologies: nMode-Locked Fiber Oscillator nCFBG (designed with both 2 nd and 3 rd order dispersion compensation matched to the compressor) nModelling tools for bandwidth optimization nDielectric Grating

5. SOUTHAMPTON Mode locked fiber oscillator pump HR SESAM Yb +3 Fiber nDiode pumped nRobust self start (SESAM) nPolarization rotation mode- locking nPulse energy ~ 60pJ at ~50 MHz nLow amplitude noise See: L. LEFORT, et Al., Optics Letters, v27 pp291 (2002)

6. SOUTHAMPTON Chirped Fiber Bragg Grating nFiber stretcher nDesigned with both 2nd and 3rd order dispersion compensation matched to the compressor nBandwidth ~12nm n~2.5dB reflectivity variation nMinimal spectral ripple (measured at 0.01nm resolution) See also: G.IMESHEV, Optics Letters, v29 pp679 (2004)

7. SOUTHAMPTON Large Mode Area Fiber nCore: diameter=20µm, N.A.=0.06 nInner cladding: diameter=200µm, N.A.=0.5 nV=3.77 nOutput M 2 ~1.06 at bending diameter~11cm nSlope efficiency ~77%

8. SOUTHAMPTON Bandwidth Modelling nA modelling tool was used for predicting the performance of complex Yb- fiber amplifier systems (prediction accuracy shown for single amplifiers below). nSimulations were applied to the design of our broad bandwidth multi-stage amplifier system. See: F.HE, et Al., Optics Express v14 pp12846 (2006)

9. SOUTHAMPTON Dielectric Grating nAdvantages:  High efficiency  High compression factor (larger size compared with silica transmission gratings)  High damage threshold (~10 times of gold gratings)  High average power handling nSpecifications of the grating in use  Groove density ~1780 l/mm  Size ~10cm*20cm  Efficiency ~95% See: J.BRITTEN, et Al., QELS 2005, JFB5

10. SOUTHAMPTON Experiment results nAverage output power ~135 W (at final amplifier output) nPulse energy ~13.5 µJ (at repetition rate of 10 MHz) nPulse FWHM ~360 fs (assuming Gaussian shape) nTime bandwidth product ~0.6 nCompressor overall transmission efficiency ~52% nSpectral clipping due to the size of the grating (performance has been improved now) (10 MHz)

11. SOUTHAMPTON Progress and Future work nCompressor optimization  Spectral clipping is removed by applying larger gratings and mirrors nNonlinear effects  SPM  B-integral ~ π @13.5µJ  Pulse distortion observed @20µJ  SRS  We observed at pulse energy ~ 200µJ nFuture work  System with high average power (>100W) and high pulse energy (>100 µJ). and high pulse energy (>100 µJ).

12. SOUTHAMPTON Conclusion nWe demonstrated an Yb-fiber CPA system incorporating a CFBG stretcher, a cascaded chain of bandwidth-optimised amplifiers and a dielectric grating compressor. nThe system produced 135 W average power with pulse energy of 13.5 µJ. The recompressed pulse duration was 360 fs. nRobust source of high pulse energies at high average powers should further broaden the applications of femto-second fiber- based CPA systems.