absorption rate to almost 100%. This is very important fact that the control of the
laser energy contrast is essential to carry out reliable experiment repeatedly.
Systematic experimental study of absorption for relativistic laser has been carried
out with Callisto laser in the Jupiter facility in LLNL [8]. The laser is 150 fs at
800 nm with energy up to 20 J focused on 5 μm width. The target is aluminum foil
with thickness 1.5–100 μm. In this experiment, the energy ratio of the ASE pedestal
to the main pulse is 2 Â 10
À4 , one order of magnitude larger than the case of Fig. 7.7.
The experimental results are compared to 2D PIC simulation. In Fig. 7.9, almost
normal incident experimental data with angle 6 degree (Fig. 7.9a) and p-polarized
oblique incident case data (Fig. 7.9b) are plotted for the intensity-dependent
absorption fraction.
1
0.8
10 -3
10 -4
10 -5
0.6
0.4
0.2
Intensity (W/cm
2 )
Better energy
contrast
t L ~50fs
Absorption fraction
0
10 15
10 16
10 17
10 18
10 19
10 20
10 21
10 22
Fig. 7.8 Absorption fraction as a function of intensity from the experiments with three different
lasers shown in [6, 7]. Note the contrast quoted here is the ratio of energy in the ASE to that in the
main pulse (opposed to intensity contrast). [Based on Fig. 6 in Ref. 7]
0.8
0.6
0.4
(a)
(b)
Absorption fraction
Absorption fraction
0.2
0.0
10
13 10
14 10
15 10
16 10
17 10
18
|λ 2 (μm 2 W/cm 2 )
I (W/cm
2 )
From [7] (400 nm)
This experiment
(800 nm)
KALOS & Vlasov
Exp. 1
Exp. 2
10
19 10
20 10
21
10
17
10
18
10
19
10
20
10
21
1.0
0.8
0.6
0.4
0.2
0.0
Fig. 7.9 Absorption fraction of the laser energy as a function of laser intensity at an incident angle
of 6 (a) and 45 (b). Each point represents the result of a single laser shot. [Figure 1 in Ref. 8]
7.2 Laser Absorption at Solid Targets
247