Pre-Amplifier

technical contact: Udo Eisenbarth

The Pre-Amplifier employs two flashlamp-pumped Nd:glass amplifiers with free apertures of 19 mm and 45 mm diameter respectively, which are operated in double-pass mode. The input beam delivered by either the femtosecond or nanosecond frontend is stepwise magnified by Keppler telescopes up to a maximum exit beam diameter of 70 mm in order to keep the fluence within safe limits, below the damage threshold. Furthermore, a deformable mirror can correct wavefront aberrations. This mirror is actively driven in a closed-loop control cycle with a Shack-Hartmann sensor. Since the sensor is located at the end of the laser chain, the deformable mirror also precompensates wavefront aberrations introduced in the main amplifier (precompensation).

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In addition, the Pre-Amplifier uses a serratured aperture in combination with a spatial filter (pinhole) for generating round and elliptic beam shapes with an almost top-hat intensity profile. The apertures are produced as lithographic aluminum masks on glass substrates.

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Typical beam profiles at the exit of the Pre-Amplifier. Depicted are a round shape as well as an elliptic profile which is optimized for later use in the pulse compressor.

Key parameters are:

Maximum output energy (fs pulses):

8J

Maximum output energy (ns pulses):

15J

Cool down between shots:

3 min

Maximum gain (depending on spectral width):

>600 (dep. on the spectral range and beam shape)