4.6. Focal Spot Conditioning

Large aperture, high power beams such as on NIF generally produce non-diffraction limited irradiance profiles at focus because of optical aberrations on the beams caused by the large number of optical surfaces. NIF beams produce about 150 mm spots (containing 50% of the bam energy) (see Figure 4-9). To limit the peak intensity and to lower the backscatter risk from targets, the focal spot is typically conditioned using continuous phase plates, smoothing by spectral dispersion and polarization smoothing.