Two experimental areas of the HERCULES house two separate experimental vacuum chambers for gas and solid targets interaction experiments. Both chambers are connected to the Hercules (100 TW and PW) compressor chambers with vacuum beam lines (Fig. 1) and are equipped with vacuum pumps, target positioning stages, plasma diagnostics and data acquisition equipment.

Fig. 1. Petawatt compressor and vacuum beam lines.

Both experimental areas have radiation shielding. 60 cm thick cement walls surround the solid target chamber (Fig. 2) while the gas target chamber has local shielding made of lead bricks. There are a few primary experiments in solid target chamber (Fig. 3a): ion acceleration, electron transport and high harmonics generation. All these experiments require intensities in excess of 5.10²⁰ W/cm^(2) and high temporal contrast of the laser. High intensities are achieved by using a short focal length parabolic mirror (f/1 or shorter) to focus laser light into a diffraction limited spot size. For this purpose we use a 4 inch diameter dielectric coated deformable mirror (DM) (Xinetics Inc.) (Fig. 3b) with a feedback from the wavefront sensor. To achieve high temporal intensity contrast of 10^-11 a special pulse cleaning technique is implemented at the front end of Hercules. Further improvement of the laser contrast by 3 orders of magnitude will be achieved by using 2 plasma mirrors in a separate vacuum chamber. After these mirrors the laser pulse will be sent to the interaction chamber where it will be corrected for any arising wavefront errors using the DM.

Fig.2 Solid target experimental areaFig.2 Solid target experimental area

Fig.2 Solid target experimental area

Fig. 3. (a) Solid target chamber. (b) 4" Deformable mirror.

In the gas target chamber (Fig. 4) we investigate laser wakefield electron acceleration using gas jets and capillary discharge plasmas. This chamber is equipped with a sector magnetic spectrometer to study spectral characteristics of the accelerated electrons, a probe line to monitor plasma dynamics and magnetic field generation due to electron current and various optical diagnostics. By sending multi-hundreds MeV electron beams from the laser wakefield into the undulator we plan to produce ~10 femtosecond bursts of directional monochromatic keV x-rays to perform different pump-probe experiments on a table-top. In collaboration with Mike Downer's group (University of Texas) we will continue to characterize laser wakefield accelerating structures using Frequency Domain Holography. In collaboration with Paul Drake's group (University of Michigan) we will study instability of electron beams propagating in underdense plasmas.

Fig. 4. Gas target chamber.