E. M. Campbell Deputy Director, University of Rochester Laboratory for Laser Energetics Presentation at George Washington University Washington, DC 14 December 2015 Ultrahigh Brightness Laser Development at the Laboratory for Laser Energetics 1 Seed Pump Time Plasma wave Depleted pump Amplified seed EP OPAL beamline EP OPAL compressor Ultra-broadband front end OMEGA EP OPAL Short-pulse transport and focusing
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Ultrahigh Brightness Laser Development at the Laboratory … · – ~12-kJ (0.532-nm), 2.5-ns pulse pump (OMEGA EP) for OPA – large-aperture (80-cm), high-damage (300-mJ/cm2) grating
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E. M. CampbellDeputy Director,University of RochesterLaboratory for Laser Energetics
Presentation at George Washington University
Washington, DC14 December 2015
Ultrahigh Brightness Laser Development at the Laboratory for Laser Energetics
1
Seed
Pump
Time
Plasma wave
Depleted pump
Amplified
seed
EP OPAL beamline
EP OPAL compressorUltra-broadband front end
OMEGA EP OPAL
Short-pulsetransport
and focusing
Collaborators
D. Haberberger, A. Davies, S.-W. Bahk, J. Bromage, J. D. Zuegel, and D. H. Froula
University of RochesterLaboratory for Laser Energetics
J. Sadler and P. A. Norreys
University of Oxford
...and many others
2
LLE and collaborators are pursuing two paths for the development of multipetawatt, high-brightness lasers
Outline
I2270
• Raman plasma-wave amplifier
– parametric amplification of a short seed pulse by stimulated Raman scattering in a matched plasma medium
• Optical parametric amplifier (OPA) pumped by multikilojoule Nd:glass laser
– ~12-kJ (0.532-nm), 2.5-ns pulse pump (OMEGA EP) for OPA
Raman amplifiers: Exploit the nonlinear physics of laser–plasma interactions (LPI)’s
I2271
4
• Intense laser radiation can excite electrostatic waves in plasmas
Laser light propagates through the plasma
Oscillations in the plasma begin to radiate scattered light (linear Thomson scatter)
The beating of the two light waves creates a ponderomotive force, pushing the particles into the troughs of the envelope
If the bunching of the particles matches an electrostatic mode, the three waves become resonant and grow
E E E E
Electrostatic plasma wave
Step 1
Step 2
Step 3
Step 4
If there is a resonance with electrostatic modes of the plasma, instabilities can result (example SRS, SBS)
I2272
5
Raman amplifiers are “seeded” SRS.
• Simulated Raman scattering (SRS)
• Simulated Brillouin scattering (SBS)
• SRS occurs when:
• SBS occurs when:
Laser light Electron plasma wave (EPW)
Scattered-light wave
Laser light Ion sound wave (IAW)
Scattered-light wave
k k kEPW
EPW0 2
0 2
~ ~ ~= +
= +
k k kIAW
IAW0 1
0 1
~ ~ ~= +
= +
National Plasma Science reports have identified plasma-wave (Raman) amplifiers as a potential for the next generation of pettawatt-class lasers
I2273
6
Seed
Pump
Time
Plasma wave
Depleted pump
Amplified
seed
High-energy compression gratings are NOT required.
Manley–Rowe (energy and momentum conservation)
• ~pump = ~seed + ~EPW
• kpump = kseed + kEPW
• Plasma [EPW (dne/ne ~1%)] is the medium that transfers energy from a long-pulse (ns) pump, high-energy laser to a short-pulse (~15 fs), low-energy seed laser
Raman amplifiers require understanding and control of nonlinear plasma physics
I2274
• Goal: efficient energy transfer from long pulse pump to seed
– pump depletion
• Challenges that limit efficiency and resonance condition and brightness (focusability)
– filamentation– frequency detuning– amplitude of EPW
- wave breaking- mode coupling
– competition with plasma-wave interactions- Raman forward scattering of the seed pulse- Raman backscatter of the pump pulse
7
Pump intensity and plasma density are key controlling parameters.
– /v k n n
c1ph
e c0
0~= =
– /index of refractionn n n1 /plasma e c
1 2=^ ^h h
Low-light pressure
Low-light pressure
Laser“Hotspot”
High-lightpressure Laser light
self-focuses
Electrondensity
Multidimensional particle-in-cell (PIC) codes have identified operating parameters for efficient pump-seed conversion
I2275
• Strategy
– maximize Raman amplification of the pump
- limit forward Raman scattering (gain < 10)
– limit filamentation of the seed (gain < 10)
• Strategy defines experimental parameters
– Ipump < 5 × 1014 W/cm2
– 2.5 × 1018 < ne < 5 × 1018 cm–3
– Iseed < 4 × 1017 cm3
8
n/n
c
10–3
10–2
1012 1013
Pump intensity (W/cm2)
1014 1015
30
25
20
15
10
5
0
psto fsps
to fs
nsto ps
nsto ps
3535 2020
6060
40404545
Max
imu
m p
rop
agat
ion
dis
tan
ce (
cm)
1150
1140
1130
1120
1110
1100
109031 5 7
Plasma density (×1018 cm–3)
See
d w
avel
eng
th (n
m)
1.00.8
0.6
0.4
0.2
0.01000 1050 1100950 1150
Wavelength (nm)
Sp
ectr
a (n
orm
aliz
ed)
SignalIdler
A tunable seed laser is being built to access the optimal Raman amplification regime for a 1053-nm pump laser
E23502b
9
The plasma density and seed wavelength will be varied to optimize amplification.
The multikilojoule Nd:glass OMEGA EP laser can serve as a pump for an OPA
I2287
• OMEGA EP
– four beams
- ~50 kJ at 1.05 nm
- >25 kJ at 0.53 nm
- >16 kJ at 0.35 nm
15
EP OPAL is an OPCPA* system, consisting of an ultra-broadband front end, large-aperture NOPA’s,** a compressor, and focuses on the OMEGA EP target chamber
Short-pulse coatings 3 5 Active R & D " Lab-scale prototype
Short-pulse diagnostics 3 6 Active R & D " Pilot-scale prototype
Ultra-broadband dispersion control 3 6 Active R & D " Pilot-scale prototype
NOPA gain adjustment 2 6 Technology concept " Pilot-scale prototype
Ultra-broadband front end 5 6 Lab-scale prototype " Pilot-scale prototype
LLE vision: three world-class user laser facilities
I2289
• OMEGA (60 beams)
– 30 kJ
– 30 TW
– 0.35 nm
27
• OMEGA EP (four beams)
– four beams (option 1)
- ~16 kJ
- ~8 TW
- 0.35 nm
– two beams (option 2)
- ~2 kJ
- ~10 ps
- 1.05 nm
• EP OPAL (one beam)
– one beam
- ~1.5 kJ
- 20 fs
- ~0.83 to 1 nm
Backup
28
A number of petawatt facilities are operational, but multipetawatt facilities are only in development
E24284a
29
Name Facility Technology Peak power Status
Apollon-10P
Laboratoire pour l’Utilisation des Lasers Intenses + Laboratoire d’Optique Appliquée +
Institute Optique
OPCPA + Ti:sapphire 5 PW Under
construction
L4
Extreme Light Infrastructure-CZ +
National Energetics
OPCPA + Nd:glass 10 PW Under
contract
–Extreme Light
Infrastructure-NP + Thales
OPCPA + Ti:sapphire 2 × 10 PW Under
contract
Vulcan 20 PWRutherford Appleton
Laboratory (RAL)OPCPA 20 PW On hold
Exawatt Center for
Extreme Light Studies
Institute of Applied Physics (IAP) OPCPA 12 × 15 PW Concept
The UFE consists of a white-light–seeded chain of NOPA’s and a 1.5-ns stretcher
E24303b
30
Oscillator
1053 nm160 fs
Delayand sync
CompressorNOPA12~
2~
NOPA2
NOPA3
Dazzler™
Beam relay
Stretcher
WLC
Yb fiber
Fiber CPA pump laser
250 fs, 14 nJ, 500 kHz 5 nJ, 0.3 ps
0.3 mJ, 1.5 ns
11 ps, 70 mJ, 5 Hz
Stretch
Nd:YLF pump laser
Regenwith SPM
compensation
527 nm 810 to 1010 nm 1053 nm
Poweramplifier
A UFE prototype has been built and testing is underway
E24316a
31
• All parameters measured so far meet requirements
• Testing will be ongoing
– operational maturity
– spectral phase control for recompression
– temporal contrast and prepulses
• A new stretcher is required for an EP OPAL-scale compressor
– prototype: 1.5 ns/200 nm (7.5 ps/nm)
– EP OPAL: 2.5 ns/150 nm (16.6 ps/nm)
Ultra-broadband front end for MTW OPAL
High power and intensity require large-aperture beams that are tightly focused
E24283a
32
• Damage thresholds for femtosecond mirrors and gratings are in the 100’s of mJ/cm2 range (cf., few J/cm2 for ps)
• Tight focal spots place challenging requirements on the beam wavefront and the final-focusing optics
20
10
30
50
70
90
40 60
Beam full width at 1% (cm)
Power versuscompressor-beam size
Pea
k p
ow
er (
PW
)
80
Grating fluence = 300 mJ/cm2
100 mJ/cm2
200 mJ/cm2
20-fs pulse (FWHM)
43
2
4
6
8
10
5 6 6 8
Focal spot FWHM (nm)
Intensity versusfocal-spot width
Inte
nsi
ty (
× 1
023
W/c
m2 )
9 10
P = 75 PW
I = P/rR2
50 PW
25 PW
EP OPAL performance depends on the grating fluence and compressor beam size
E24286d
33
Grating fluence (20 fs)
100 mJ/cm2
Compressor beam size (FW 1%)
60 × 60 cm
Diagonal for 45° angle of incidence 110 cm
Compressor output energy 300 J
f-number and focal spot (nm)
f/6 13
f/1.3 4.2
Energy on target 290 J 230 J
Power 14 PW 12 PW
Intensity (W/cm2) 1 × 1022 9 × 1022
300 mJ/cm2
60 × 60 cm
110 cm
900 J
f/6 13
f/1.3 4.2
860 J 700 J
43 PW 35 PW
3 × 1022 3 × 1023
300 mJ/cm2
80 × 80 cm
149 cm
1600 J
f/4.6 10
f/1 3.2
1500 J 1200 J
75 PW 62 PW
1 × 1023 8 × 1023
Advancedgratings
Increasedbeam size
Limited by size of current optics fabrication Full scale
Challenges remain to scale femtosecond coating capability for meter-scale laser applications
G10251c
34
• Current uniformity for 1 m " masks with phase discontinuities
• Scaling femtosecond system geometry " 3.5-m chamber
• High film stresses for fully dense coatings
• m/4 on a 1-m optic would require ~16-cm thickness (4-nm-thick coating)
• Match the dispersion over a curved optic aperture
• Enhanced/protected metals are preferred with sufficient laser-damage thresholds
Laser-damage thresholds at the correct pulse length, spectral bandwidth, and large aperture are critical to successful system scale-up.
Enhanced-metal coatings have been developed for the compressed-pulse section
E24318a
35
• Several practical benefits for short-pulse transport – femtosecond damage thresholds comparable to dielectric mirrors – s- or p-polarized beam – low group-delay dispersion, stress-induced wavefront and sensitivity
to coating thickness
R (p-pol, 810 to 1010 nm) >97.4% >98.6% >99.3%GDD** (810 to 1010 nm) 2 fs2 13 fs2 35 fs2