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Pre-Amplifier
The Pre-Amplifier employs three flashlamp-pumped Nd:glass amplifiers (2 x 19 mm diameter and 1 x 45 mm). 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 abberations. This mirror is actively driven in a closed-loop system 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.
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Schematic overview of the PHELIX Pre-Amplifier. The overall path length (input to exit) is about 12 m.
The PHELIX Pre-Amplifier. In order to avoid plasma formation in air of the focussed beam major parts of the beam path are build in vacuum tubes. In the picture's center one can see the 45 mm amplifier.
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.
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): |
5 J |
| ● Maximum output energy (ns pulses): |
10 J |
| ● Cool down between shots (19mm heads): |
3 min |
| ● Cool down between shots (45mm head): |
10 min |
| ● Maximum gain (depending on spectral width): |
> 200 |
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