1. Trident Laser Facility
Introduction to Laser-Plasma Interaction
(LPI) Physics
David S. Montgomery
LPI Principal Investigator
Plasma Physics Group (P-24)
Physics Division
Los Alamos National Laboratory
Onset behavior of SRS
Langmuir Decay Instability
cascades
4040
4080
4120
4160
ls (Å)
10Å
Los Alamos
Trident Laser Facility
Very exciting results obtained on the Trident laser that are:
- Good Science
- Can have a large impact on ICF program

2. Laser Plasma Interaction: extreme physics
target
Laser Intensity: W/cm2
(30,000 GV/m)
Pulse Widths: sec
Temperatures: °C
Plasma flows: cm/sec
(100’s mile/sec)
Plasma size: 1 µm - 1 mm
laser
• Inverse Bremsstrahlung
Absorption (e-i collisions)
• Parametric Instabilities
ncr
laser
scattered light
Heat
transport
fast
particles
X-rays

3. Major U.S. high-power laser facilities
Omega Laser
(Univ. of Rochester)
30 kJ, 30 TW
Z Backlighter
(Sandia, Albuquerque)
under construction, 40 kJ, 20 TW
Trident
(Los Alamos)
500 J
NIF - National Ignition Facility
(Livermore)
under construction, 2 MJ, 500 TW
Nova Laser
(Livermore)
Defunct
30 kJ, 30 TW
Nova
Target chamber
(defunct)

4. Cool Laser Fusion Pictures
X-ray micrograph of Hohlraum experiment on Omega
Inside Omega chamber
during a fusion experiment
NIF target chamber
(under construction)
Fusion Yield (DT) ≈ 1014 (14.1 MeV) neutrons
~ 300 J of fusion energy
~ 30 kJ of laser energy
~ 1% fusion yield
30 ft. dia.
1 million lbs.

5. Several important laser-plasma applications have been developed over the years
Heat
outside
• Inertial Confinement Fusion (laser fusion)
• X-ray lasers
• Plasma-based accelerators
• VUV and X-ray lithography
• Plasma processing
• Remote sensing (laser-induced breakdown spectroscopy)
• Ion, proton beam production
• Basic and applied physics research
- direct nuclear excitation
- high energy-density physics (high Te, pressure, density)
- laboratory astrophysics
- laboratory general relativity simulations?
- others... DT
Implosion
Fusion
Energy!!!

6. Plasma oscillations have a simple analogy to a mass on a spring
mass M suspended on a spring of constant k
(spring provides restoring force F = kx) k
Eq. of motion M x
x(t) = A sinwt + B coswt
mass oscillates with frequency w

7. Electron Plasma Oscillations: a simple derivation
Electric field is
restoring force
No magnetic Field
(B=0)
plasma uniform
density ne x
test electron
wp is the plasma frequency

8. Electron Plasma Wave Derivation: advanced
Continuity Eq.
Force Eq.
Goal: develop wave equation for density fluctuations.
Assumptions: B=0, small amplitude ∂n, fixed ions, adiabatic

9. Background on Waves in Plasmas
• Waves in unmagnetized plasmas
Electron Plasma Wave (EPW) or Langmuir wave
Ion Acoustic Wave (IAW)
Electromagnetic Wave (EMW) or Light wave
BACKUP
(c = ln)

10. Parametric instability of coupled oscillators: a mechanical analogy
Resonance occurs when the “driving frequency” w0 equals the
sum of the two “daughter” oscillation frequencies:
w0 = w1 + w2, oscillation amplitude exponentiates!! k1 k2 w0 w1 w2
w12 = k1/M1
w22 = k2/M2 M1 M2

11. Parametric coupling between intense laser wave, plasma wave and scattered light wavedn
Parametric Instability
Feedback loop
Self-focusing (filamentation)
high ne
low ne
intensity
increases
laser
hotspot
JT ~ dnE0
Force ~ (ES E0)
Instability occurs when growth rate
exceeds damping of wave energy in
interaction volume
Interplay and competition can occur
between these instabilities
Instabilities Remain a
Threat to ICF
Nova large plasma experiments
Up to 50% SRS
Up to 30% SBS
scattered wave ES
SRS and SBS:
• energy loss
• scattered light in undesired locations
• preheat due to hot electrons (SRS)
(killed Helios and Shiva)
• potential damage to NIF optics (SBS)
Self-focusing
• beam breakup, spraying, steering
• enhance SRS, SBS

12. Some of the important parametric decay mechanisms for laser plasmas
stimulated Brillouin scattering
(SBS)
stimulated Raman scattering
(SRS)
EMW
EPW
IAW
laser
EMW
Parametric Decay Instability
(PDI)
Two-plasmon Decay
(TPD)
EPW
IAW
EPW
laser
laser
EPW
IAW
Langmuir Decay Instability
(LDI)
EPW

13. Typical setup for a laser-plasma interaction experiment
beam-splitter
diagnostic
lens
focusing
lens
target
or plasma
incident
laser
Wavelength (nm)
Scattered light
diagnostics
• Energy, Power
• Spectra
• Images
X-rays
(energy, spectra, images)
particles

14. Typical day of shots at Omega (7am - 11pm)
Experiments team &
Junk food
Hmm… what’s for
lunch??
I want to
go home
now...
David, almost the
end of the day...
Experiments Team
Deciding who’s going
to pick up dinner...
I’m running the shot...
I’m really in
charge...
It’s not my
turn...
I went last
time...

15. Summary and Conclusions
• Laser-Plasma Interaction Physics
- extreme physics in a small lab environment
- complex, challenging
- interesting applications
• Laser Fusion
- Laser-plasma instabilities a potential threat
- need for understanding in order to control instabilities
Laser-plasma interaction physics is a challenging
and exciting area of research