  Ultrahigh peak power lasers are important scientific tools for frontier
laser-physics researches, in which both the peak power improvement and
operating safety are very important meanwhile limited by the damage threshold
and size of compression gratings currently. Based on a recent reported method
"multistep pulse compressor (MPC)", a multistage smoothing based MPC (MS-MPC)
is proposed here to further improve the running safety, operating convenience,
and simplify the whole setup of the MPC. In this optimized design, the beam
smoothing is not simply executed in the pre-compressor or main-compressor, but
separated into multistage. Then, it can protect important optics in every stage
directly and reduce the executing difficult of typical MPC at the same time.
The prism pair based pre-compressor will induce suitable spatial dispersion
which is easier to be achieved and enough to protect the first grating
directly. At the same time, the asymmetric four-grating compressor (AFGC) will
also induce spatial dispersion to further smooth the laser beam which helps to
protect the last grating directly. In this way, 10s-100s PW lasers can be
compressed by using current available optics with improved operating safety
owing to remove random spatial intensity modulations. Furthermore, an
additional beam smoothing stage can be added before the main amplifier to
protect the biggest amplification crystal away from damage. This MS-MPC optical
design can be easily extended to be used in all exist PW laser facilities to
improve their potential compressed pulse energy and running safety.
