7.8.4 Common Rule of Better Coupling
It is challenging to predict the absorption fraction and hot electron temperature based
on some theory even for simple targets. It is more challenging when the relativistic
lasers are irradiated on a variety of structured targets. The physics of such relativistic
laser and plasma interaction will be reviewed later. Within the experimental and
computational results, nevertheless, it is seen that laser-matter coupling is enhanced
and the hot electron generation is also enhanced in energy conversion rate and
average energy (temperature) with use of complicated targets. Such resultant
knowledge helps the engineering applications of ultra-intense lasers. Let us
summarize the common role in the structured targets. We can enumerate the
following advantage compared to the flat target case:
1. The structured plasma can confine the electrons for a long time in the laser
interaction region.
2. The laser is also controlled so that the effective interaction surface with plasmas is
enlarged by a complicated structure.
3. The laser is reflected in the structure, and a complicated laser intensity
distribution is formed, enhancing the stochastic heating and direct laser.
4. The sheath field and self-generated DC magnetic field, to be explained below, are
generated and are used to confine the hot electrons inside the structured region so
that they gain more energy via interaction with laser electric field.
7.9 Magnetic Field Generation
Strong non-oscillating magnetic field generation is observed when intense or ultraintense lasers are irradiated on any kind of materials. In the case of relativistic intense
lasers, the strength of non-oscillating magnetic field is roughly evaluated by a
dimensional analysis as follows:
d
dt
p ¼ Àev  B ) B $
mω
eN
$
107
N
MG
½
for λ ¼ 1 μm
ð
Þ ,
ð7:9:1Þ
where we assumed p ~ mc and v ~ c. The time derivative is replaced with the pulse
duration (¼N/ω), where N is the number of oscillation. Anyway, roughly speaking
magnetic field of the order of tens of mega-gauss is possibly generated as DC field
over the laser pulse duration.
It is better compared to the strength of laser magnetic field. It easily shown
B 0 ¼ E 0 =c ¼
mω
e
a 0 ¼ 107a 0 MG
½
ð7:9:2Þ
107 MG is the strength for a 0 ¼ 1.
7.9 Magnetic Field Generation
279
It is challenging to predict the absorption fraction and hot electron temperature based
on some theory even for simple targets. It is more challenging when the relativistic
lasers are irradiated on a variety of structured targets. The physics of such relativistic
laser and plasma interaction will be reviewed later. Within the experimental and
computational results, nevertheless, it is seen that laser-matter coupling is enhanced
and the hot electron generation is also enhanced in energy conversion rate and
average energy (temperature) with use of complicated targets. Such resultant
knowledge helps the engineering applications of ultra-intense lasers. Let us
summarize the common role in the structured targets. We can enumerate the
following advantage compared to the flat target case:
1. The structured plasma can confine the electrons for a long time in the laser
interaction region.
2. The laser is also controlled so that the effective interaction surface with plasmas is
enlarged by a complicated structure.
3. The laser is reflected in the structure, and a complicated laser intensity
distribution is formed, enhancing the stochastic heating and direct laser.
4. The sheath field and self-generated DC magnetic field, to be explained below, are
generated and are used to confine the hot electrons inside the structured region so
that they gain more energy via interaction with laser electric field.
7.9 Magnetic Field Generation
Strong non-oscillating magnetic field generation is observed when intense or ultraintense lasers are irradiated on any kind of materials. In the case of relativistic intense
lasers, the strength of non-oscillating magnetic field is roughly evaluated by a
dimensional analysis as follows:
d
dt
p ¼ Àev  B ) B $
mω
eN
$
107
N
MG
½
for λ ¼ 1 μm
ð
Þ ,
ð7:9:1Þ
where we assumed p ~ mc and v ~ c. The time derivative is replaced with the pulse
duration (¼N/ω), where N is the number of oscillation. Anyway, roughly speaking
magnetic field of the order of tens of mega-gauss is possibly generated as DC field
over the laser pulse duration.
It is better compared to the strength of laser magnetic field. It easily shown
B 0 ¼ E 0 =c ¼
mω
e
a 0 ¼ 107a 0 MG
½
ð7:9:2Þ
107 MG is the strength for a 0 ¼ 1.
7.9 Magnetic Field Generation
279