Bin Qiao
Office: Room 544 (South), Physics Building
Tel: 62745005
2014 Autumn Semester, course for graduate student Lecture notes: Physics of Laser-Plasma Interaction
What is Laser? Laser—Laser Amplification by Stimulated Emission of Radiation Before the Birth of Laser : Albert Einstein (1916-1917)
Stimulated Emission
1. EINSTEIN, ALBERT. Strahlungs-Emission und -Absorption nach der Quantentheorie [Emission and Absorption of Radiation in Quantum Theory]. Verhandl. D. Deutch. Phys. Ges., 1916, Vol 18, pp. 318-323.
2 EINSTEIN ALBERT Z Q t th i d St hl [O th Q t Th f R di ti ] Ph ZS 19172. EINSTEIN, ALBERT. Zur Quantentheorie der Strahlung [On the Quantum Theory of Radiation]. Phys. ZS., 1917, Vol. 18, pp. 121-128.
EINSTEIN, ALBERT. Strahlungs-Emission und -Absorption nach der Quantentheorie [Emission and Absorption of Radiation in Quantum Theory]. Verhandl. D. Deutch. Phys. Ges., 1916, Vol 18, pp. 318-323.
EINSTEIN, ALBERT. Zur Quantentheorie der Strahlung [On the Quantum Theory of Radiation]. Phys. ZS., 1917, Vol. 18, pp. 121-128.
Maiman(1958) Laser: Light Amplification by Stimulated Emission of Radiation
Theodore Harold Maiman
Maiman(1958) Laser: Light Amplification by Stimulated Emission of Radiation
Theodore Harold Maiman
Key laser parameters 1. Power
ξLPL = ξL τ ,
1/2 (V /m),
: laser energy, τ : pulse duration (FWHM)à fs to ns
Units : J/s (W) ; range from 10-6W to 100s of TW (Terawatt, 1012W) up to Petawatt
2. Intensity S = πr2 : the area of laser focal spot
Units : W/cm2; range from 1014~1015 W/cm2 (conventional ICF), 1018~1024 W/cm2
3. Electric field
4. Wavelength and frequency
= 2πc ωL
, λL =1.053µm : Nd glass laser λL =10.6µm : CO2 laser λL = 0.35µm, 3ω laser (ICF)
Key laser parameters
10 2 2 1/ 2 0 8.5 10 [ ( / ) ( ) ]La I W cm mO P u
I0 (W/cm2)
1016 5u1016 1017 5u1017 1018 5u1018 1019 5u1019 1020 1021
8.37 26.55.922.651.87140.8370.5920.2650.1870.084a0 (O0=1Pm)
2 18 2 21.37 10 ~LI W cm m v cO P u
TXLYHU
Normalized laser amplitude a0 = eE0 /mecω0
Laser progress
2 ultrarel p
2 comp rel
e E = m c e E = m c e E = m c
O O
Fundamental intensity dependent regimes of interaction
Very compact accelerators can be built
a0 = posc mec
Laser progress
Courtesy of Prof. Todd Ditmire, UT Austin
What is plasma? Plasma: A plasma is a quasineutral “gas” of charged and neutral particles which exhibits collective behavior. (F. F. Chen) Coulomb Because the plasma is composed of charged particles, the electromagnetic fields govern their motion, and the motion changes the electromagnetic fields in turn. Therefore, the particle motion and the EM fields are strongly coupled. The plasma properties appears only when a gas is ionized sufficiently that the electric characters are more significant than the neutral characters. By “collective behavior”, which means that depend not only on local conditions but on the state of the plasma in remote regions as well. Collisionless plasma: The long range EM force is much larger than the local force associated with collisions.
What is plasma? Quasineutral:
E = 4 3 πr3 ncr
106 e r2 = 6×109 r(V /m)
2. ωp
n(r, t) = n0 + !n (r, t), ni = n0, !n << n0 ∇⋅E = −4π $n e
∂n ∂t +∇⋅ (nu) = 0
me ∂u ∂t = −e E
∂2 "n ∂t2
What is plasma? Quasineutral:
O /|| 02 ,4
”(quasineutral)“
ni|ne| n(n )

Derivation of Debye Length
n = n0 exp(e / kBT ) !n = !nδ(r)
e(r) / kBT <<1
≈ 4πn0e
2
λD = ( kBT 4πn0e
1) OD<<L,OD;
LOD L

OD<<L
2) ND>>>1,1 ;
22 3
443 4
3 4
ne kT
3) ZW>1,


Key plasma parameters 1. Debye length
λD = ( Te
4πn0e 2 ) 1/2,
• Screen radius of the electrostatic potentials • Local spatial dimension of charge separation
2. Critical density of laser propagation:
ω 2 =ω pe 2 + c2k2 nc =ω0
2me / 4πe 2 =1.1×1021 / λL
2
vg = dϖ dk
vp = ϖ k =
ϖ pe 2
ϖ 2 = 1− ne ncr
Laser propagation always from low to high refractive index à from high to low plasma density region
4. Plasma density scale length: L = (1
n ⋅ dn dx )−1 n = n0 exp(−x / L)