1. Max-Born-Institut M.Boyle, A.Thoß, N.Zhavaronkov, G.Korn Max Born Institute; Max-Born-Str. 2A, 12489 Berlin, Germany T.Oksenhendler, D. Kaplan Fastlite, Xtec,Ecole Polytechnique, 91128 Palaiseau Cedex,France Amplitude and phase shaping in a high average power 1kHz CPA-laser Motivation To create designer temporal shapes from active control of spectral phase and amplitude components Temporally modulated shapes used for optimization of laser and experimental systems, for example: GVD Compensation Amplifier output bandwidth increase signal output from feedback controlled physical processes (ionization and fragmentation of molecular species and x-ray generation) Further amplification to 10-100W Schematic of Modulator Operation of Modulator z(  ) Ordinary (fast) Extraordinary (slow) The pulse is shaped by acousto-optic modulation. The pulse enters along the ordinary axis of a crystal and with a rf signal. Individual frequency components are coupled to the extraordinary axis and then compose the shaped pulse. [F.Verluise, et al. Optics Letters April 15, 2000] Results Shaping Results after Amplification: A LabView interface allows the user tp adjust pulse separations and ratios easily with the Dazzler acousto-optic modulator. In the example on the left, the left panel shows the calculated spectrum resulting from a pulse separation of ~1800 fs with equal pulse heights (shown on the right plot). Amplification of this ‘double pulse’ resulted in a pulse train of numerous equally spaced pulses dependent on amplitude ratio. Pulse amplitude ratio Control of number of pulses Reason why this happens: Auto-correlation for different ratios of pulse amplitudes The closer the ratio is to 1:1, the increased number of pulses. Practical Result: High order nonlinear temporal diffraction of overlapping pulses in the stretched pulse*. *[Ref Liu, et al Optics Letters, 20, 1163-1165 (1995)] An adaptive feedback control loop was developed for optimization. Each pixel is varied randomly while the desired output signal is maximized. In the graph on the right, the SHG signal from auto- correlation was optimized after detuning the amplifier by one round trip. The result was better than if the detuned pulse was compressed correctly, which indicates the procedure compensates for the higher order dispersion. Results Optimization: Conclusions and Future: Amplitude Shaping Results: The oscillator spectrum is shown on the left for various depths of a transmission hole. The resulting amplifier spectrum is shown on the right for the two indicated cases. Temporal modulation of femtosecond pulses allows for the laser-matter interaction to be controlled in a desired manner. Many physical systems require high energy pulses and thus the shaped pulses need to be amplified. It has been demonstrated amplitude and phase pulse shaping can be done prior to amplification, although the nonlinear amplification must be considered in generating arbitrary shapes. The extension seems possible to 100W. For Further Info: boyle@mbi-berlin.de