4.6.1 Continuous Phase Plates

A continuous phase plate (CPP) is an optic that is presently located in the NIF final optics assemblies (FOA) between the SHG and the THG crystals. CPPs consist of deterministically imposed surface variations that add phase aberrations to the laser beams propagating through them. A typical CPP surface profile is shown in Figure 4-10. The effect of these phase aberrations is to broaden the focal spot profile in a controlled manner.

Figure 4-9

Figure 4-9. Typical focal spot of the NIF beam without a phase plate.

Figure 4-10

Figure 4-10. Example of the surface profile of a typical continuous phase plate (CPP).

Different CPP phase profiles can be applied to produce different sized focal spots. Table 4-3 below lists currently available CPP designs for use on NIF and the present default installation on the NIF beamlines. Figure 4-11 shows the expected focal spot sizes for the four currently installed CPP designs on NIF. The user can request removal of the CPPs from selected beamlines for a given experiment and can also request replacement of the default CPPs with the 400 mm designs in selected beamlines.

Figure 4-11

Figure 4-11. Focal spots for the default CPPs currently installed on NIF beamlines.

If a user requires CPP designs (focal spots) other than those listed in Table 4-3, adequate time and resources need to be allocated for the design, fabrication, installation and commissioning of the new CPPs on NIF beamlines. Users are encouraged to work with the NIF final optics team to realize this.

Table 4-3. Currently available CPPs for use on NIF.

Table 4-3