Page 422 - High Power Laser Handbook

390 So l i d - S t at e La s e r s The National Ignition Facility Laser 391

1.0
Calculated
Measured
0.8 1.0 MJ
Encircled energy fraction 0.6 1.8 MJ

0.4

0.2

0.0
0 200 400 600 800 1000 1200
Major axis radius (µm)

1.000
Calculated
Measured
Fractional power above intensity 0.100 1.8 MJ 1.0 MJ

0.010

0.001
0 0.5 1.0 1.5 2.0 2.5
15
2
Intensity (10 W/cm )
Figure 14.31 Comparison of the encircled energy fraction and the fractional
power above intensity (FOPAI) for the 1-MJ and the 1.8-MJ shots described in
Fig. 14.30. The encircled energy was calculated in elliptical coordinates, with
eccentricity of 0.55 for the 1-MJ case and 0.88 for the 1.8-MJ case. The total
power is normalized to 1 TW for each case.

is separable in time and space: I(x, y, t) = F(x, y)*P(t)/E, where F is the
measured near-field fluence, P the time-dependent whole-beam
power, and E the total energy. Equation (14.2) is, again, evaluated at
the time of peak power. Our models indicate that for these pulses,
intensity-dependent effects, such as nonlinear refractive index and
frequency conversion, do not cause significant changes in the focal
spot characteristics as a function of time, thus justifying the separability