Focusing quality of a split short laser pulse

For multiple laser pulse experiments, it is necessary to split a laser pulse. In order to split a short laser pulse without stretching the pulse width, the laser pulse should not pass through thick materials. For this reason, a pellicle beam splitter (BS) and/or a mirror with a hole are required as a BS for the short laser pulse. The focusing qualities of the laser pulse after passing through the pellicle BS and the mirror with a hole are the same as without the BS's. The laser pulse quality reflected by the BSs should be considered for the laser pulse. A pellicle BS is a thin foil, so, it is weak against vibrations. One should be careful about airflows and isolation from vibration sources. The spot size of the reflected laser pulse is consistent with the size reflected by a normal mirror. The energy loss is about 10% compared with a normal mirror. A mirror with a hole is strong against external vibrations. The reflected laser pulse has a doughnut shape. The reflected laser pulse is interfered due to the shape. In order to cleanly focus the laser pulse, the inside size of the doughnut should be smaller than a half size of the outside portion of the doughnut.