Fig. 1. Scheme of the principle of the SEPPL (blue boxes) integrated into the PHELIX facility (black boxes). It shows the main components of the SEPPL, namely the pulse conditioning, amplification, pulse compression and transport of the pulse.

Fig. 2. Schematic drawing of the seed-pulse conditioning. The incoming pulse can be sent into the FPC (dark blue mirrors), which can also be bypassed before sending the output pulse into the fiber coupler. In addition, a sample of the FPC transmission is monitored on a camera to control the cavity alignment.

Fig. 3. Schematic drawing of the regenerative amplifier with a total size of 915 mm × 455 mm. The input pulse enters the amplifier through a fiber coupler (red input), passes two Faraday isolators and enters the main cavity, delimited by the flat and concave mirrors (blue). The cavity is set up around a Yb:YAG crystal, which is being pumped by a 12-pass pump system, powered by a laser diode.

Fig. 4. Dependency of the pulse duration at 1030 nm (black) and 515 nm (blue) on the length of the FPC used for the seed generation. The black and blue lines correspond to the calculated pulse duration at central wavelengths of 1030 and 515 nm, respectively, given by the cavity ring-down using a reflectivity of 99.7% for both mirrors.

Fig. 5. Shape of the pulse duration using FPC distances of 0.3 mm (purple), 1.3 mm (yellow) and 2.3 mm, as well as the resulting pulse using the overload (OL) mode of the amplification cavity (blue).

Fig. 6. Pulse duration stability over 23 minutes for different FPC lengths. Only the shortest cavity shows a deviation after 10 minutes.

Fig. 7. Experimental setup using the SEPPL as a probe laser for the characterization of a preplasma induced by the PHELIX laser. The probe can be sent into an MZI for measuring the density profile or used for streaked shadowgraphy of the plasma expansion.

Fig. 8. Streaked shadowgraphy of a 20 μm thick gold target located at μm. The initial position is indicated by the red dashed lines. The laser hits the target at from the left-hand side, leading to an expansion of the plasma, which is monitored for a duration of almost 10 ns.

Fig. 9. The left-hand side shows an interferometric measurement of a plasma expansion, and the inlet shows a zoomed region of the resulting interference fringes. The right-hand side shows the electron density distribution, extracted from the plasma refractive index of the left-hand side measurement.