The pulse shape and timing are common for all four beams within a single quad. Each quad may be independently configured for timing and pulse shape. NIF has the capability to produce a wide variety of precision pulse shapes. The flexibility of the pulse shaping is limited between the two quads within a single bundle due to amplifier configuration and residual gain issues.
In order to request a pulse shape, the user enters the desired pulse shape and energy at the target through the shot setup. This request is then transformed to a Master Oscillator Room (MOR) pulse shape request through the LPOM setup calculations, which take into account the pulse shape distortions due to the main laser gain saturation and also due to the frequency conversion. The requested MOR pulse shape is then created using an arbitrary waveform generator (AWG). The maximum pulse width for any quad is currently limited to 30 ns due to the current MOR pulse-shaping hardware and the regenerative amplifier round-trip time. Figure 4-6 shows some recent examples of the sorts of pulses that can be generated on NIF. In addition to shaped pulses, NIF also can generate 88 ps full width at half-maximum (FWHM) Gaussian pulses (called “impulses”) used for point x-ray sources.
Figure 4-6. Some recent examples of pulse shapes delivered on target on NIF. In the lower right image, a longer than 30 ns pulse at the target chamber center (TCC) is generated by concatenating two under-30 ns pulses from different quads.