The final stage of the Z-Beamlet short-pulse efforts will be the Z-Petawatt facility. The Compressor for Z-Petawatt will be located in Building 983, where the Z-Accelerator is located. Thus the beam transport from compression to target (Z) will be minimized. A seperate Petawatt targe tarea will be installed, too.
Z-Petawatt will use 94cm gold compression gratings which have been poduced at Lawrence Livermore National Laboratories and were used with the Livermore Petawatt laser before its shutdown in 1999. As grating technology improves, These gratings may later be replaced by multi-layer-dielectric (MLD) gratings, which tolerate higher laser fluences. The compressed pulse width is epected to be 500 fs. The following table gives the approxiate specifications for Z-Petawatt:
|Z-Petawatt Specifications||Ongoing Project||Possible Upgrade|
|Year of completion||2007||?|
|Grating technology||94cm gold, double path||94cm MLD, double path|
|Output energy||400-650 J||> 1 kJ|
|Power||0.8-1.3 PW||> 2 PW|
|Possible intensities||1-7×1020 W/cm²||1021W/cm²|
An extension of the Z-Building (983) has been built to house the compressor and the new target area. The buildings for Z and Z-Beamlet/Z-Petawatt are connected via evacuated relay telescopes for laser beam transport. There is a beam transport line for both laser systems, and either one can be transported and focused into the Z-Target chamber. The laser target area next to the Z-Petawatt compressor can be served by both systems simultaneously. The picture below shows a technical drawing of the two buildings (986:Z-Beamlet/Z-Petawatt below and 983: Z above) with the double laser installation.
The final focus optic that has to be installed for Z-Petawatt has a unique design, which can accomodate all of the following requirements:
These requirements are met with a design using a 90 degree off-axis parabola (OAP), which has a two-wavelength dielectric coating. The converging beam is pointed by a two-wavelength steering mirror, which is the last optical element in the line of sight of the target*. The assembly of steering mirror and parabola can be rotated around the incident axis of the parabola in order to be able to steer without a deterioration of the focus. The design of the final focusing assembly has been completed, however, the construction is not yet done.
*: As the steering mirror is an expensive long-lead-time item, too, many experiments will be made with a thin debris-shield to protect this optic.