motivation
DESCRIPTION
A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Amplifier. Paul Mason, Klaus Ertel, Saumyabrata Banerjee, Jonathan Phillips, Cristina Hernandez-Gomez, John Collier Workshop on Petawatt Lasers at Hard X-Ray Light Sources - PowerPoint PPT PresentationTRANSCRIPT
A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) AmplifierPaul Mason, Klaus Ertel, Saumyabrata Banerjee, Jonathan Phillips, Cristina Hernandez-Gomez, John Collier
Workshop on Petawatt Lasers at Hard X-Ray Light Sources5-9th September 2011, Dresden, Germany
[email protected] Rutherford Appleton Laboratory,Centre for Advanced Laser Technology and ApplicationsR1 2.62 Central Laser Facility, OX11 0QX, UK+44 (0)1235 778301
Motivation• Next generation of high-energy PW-class lasers
– Multi-J to kJ pulse energy– Multi-Hz repetition rate– Multi-% wall-plug efficiency
• Exploitation– Ultra-intense light-matter interactions– Particle acceleration – Inertial confinement fusion
• High-energy DPSSL amplifiers needed– Pumping fs-OPCPA or Ti:S amplifiers– Drive laser for ICF– Pump technology for HELMHOLTZ-BEAMLINE
BeamlineFacility
HELMHOLTZ- BEAMLINE
Amplifier Design Considerations• Requirements
– Pulses from 10’s J to 1 kJ, 1 to 10 Hz, few ns duration, efficiency 1 to 10%
• Gain Medium
– Ceramic Yb:YAG down-selected as medium of choice
• Amplifier Geometry
Long fluorescence lifetime Higher energy storage potentialMinimise number of diodes (cost)
Available in large size Handle high energies
Good thermo-mechanical properties Handle high average power
Sufficient gain cross section Efficient energy extraction
Low quantum defect Increased efficiency & reduced heat load
High surface-to-volume ratio Efficient coolingLow (overall) aspect ratio Minimise ASEHeat flow parallel to beam Minimise thermal lens
STFC Amplifier Concept• Diode-pumped multi-slab amplifier
– Ceramic Yb:YAG gain medium– Co-sintered absorber cladding for ASE suppression
• Distributed face-cooling by stream of cold He gas – Heat flow along beam direction– Low overall aspect ratio & high surface area
• Operation at cryogenic temperatures– Higher o-o efficiency – reduction of re-absorption– Increased gain cross-section– Better thermo-optical & thermo-mechanical properties
• Graded doping profile– Equalised heat load in each slab– Reduces overall thickness (up to factor of ~2)
~175K
Modelling• Laser physics
– Assumptions• Target output fluence 5 J/cm²• Pump 940 nm, laser 1030 nm
– Efficiency & gain• Optimum doping x length product
for maximum storage ~ 50%• Optimum aspect ratio to minimise
risk of ASE (g0D < 3) of ~1.5– Extraction
• Extraction efficiency ~ 50%
• Thermal & fluid mechanics– Temperature distribution – Stress analysis– Optimised He flow conditions
50%
3.8
pump region
Cr4+:YAG
Yb:YAG
HiPER HiLASE / ELI
PrototypeDiPOLE
Extractable energy ~ 1 kJ ~ 100 J ~ 10 J
Aperture 14 x 14 cm200 cm2
5 x 5 cm25 cm2
2 x 2 cm4 cm2
Aspect ratio 1.4 1.2 1
No. of slabs 10 6 4
Slab thickness 1 cm 0.7 cm 0.5 cm
No. of doping levels 5 3 2
Average doping level 0.33 at.% 0.79 at.% 1.65 at.%
HiPER HiLASE / ELI / XFEL
Extractable energy ~ 1 kJ ~ 100 J
Aperture 14 x 14 cm200 cm2
5 x 5 cm25 cm2
Aspect ratio 1.4 1.2
No. of slabs 10 6
Slab thickness 1 cm 0.7 cm
No. of doping levels 5 3
Average doping level 0.33 at.% 0.79 at.%
Scalable Design
DiPOLE Prototype Amplifier
• Design sized for ~ 10 J @ 10 Hz
• Aims– Validate & calibrate numerical models– Quantify ASE losses– Test cryogenic gas-cooling technology– Test (other) ceramic gain media– Demonstrate viability of concept
• Progress to date– Cryogenic gas-cooling system commissioned– Amplifier head, diode pump lasers & front-end
installed – Full multi-pass relay-imaging extraction
architecture under construction– Initial pulse amplification tests underway
Cr4+
Yb3+
Ceramic YAG disk with absorber cladding
Diode pump laser
• 4 x co-sintered ceramic Yb:YAG disks– Circular 55 mm diameter x 5 mm thick– Cr4+ absorbing cladding– Two doping concentrations (1.1 & 2.0 at.%)
Optical Gain MaterialCr4+
Yb3+
35 m
m
55 m
m Pump2 x 2cm²
PV0.123wave
Fresnel limit ~84%
940
nm
1030
nm
Amplifier Head Design
• Schematic • CFD modelling
Uniform T across pumped region ~ 3K
He flow
He flow40 m3/hr ~ 25 m/s @ 10 bar, 175 K
PumpPumpVa
cuum
Disks
pressurewindowsvacuum
windows
Diode Pump Laser• Built by Consortium
– Ingeneric, Amtron & Jenoptic
• Two systems supplied– 0 = 939 nm, FWHM < 6 nm– Peak power 20 kW, 0.1 to 10 Hz– Pulse duration 0.2 to 1.2 ms– Uniform square intensity profile
– Steep well defined edges– ~ 80 % spectral power within 3 nm
– Good match to Yb:YAG absorptionspectrum @ 175K
Measured
20 m
m
20 mm
DiPOLE Laboratory
Cryo-cooling system
2 x 20 kW diode pump lasers
Amplifier head
Front-end Injection Seed• Free-space diode-pumped MOPA design
– Built by Mathias Siebold’s team @ HZDR Germany
• Cavity-dumped Yb:glass oscillator– Tuneable 1020 to 1040 nm
• ~ 0.2 nm– Fixed temporal profile
• Duration 5 to 10 ns– PRF up to 10 Hz– Output energy up to 300 µJ
• Multi-pass Yb:YAG boosteramplifier– 6 or 8 pass configuration– Output energy ~ 100 mJ
nsecoscillator
Booster pump diode
Amplifier crystal
100 mJoutput
Polarisation switching waveplate
x3 or x4
Initial Pulse Amplification Results
• Simple bow tie extraction architecture– 1, 2 or 3 passes– Limited by diffraction effects
• Injection seed– Gaussian beam expanded to overfill pump region– Energy ~ 60 mJ
PumpPump
SeedAmplifiedbeam
Spatial Beam Profiles @ 100K, 1 Hz
E = 2.6 J @ 10 Hz
Gain 8
Gain 6
Pulse Energy v. Pump Pulse Duration• 3 passes @ 1 Hz
• Relay-imaging multi (6 to 8) pass extraction architecture is required to allow >10 J energy extraction at 175K
5.9 J
Onset of ASE loss
Conclusions• Cryogenic gas cooled Yb:YAG amplifier offers potential for
efficient, high energy, high repetition rate operation– At least 25% optical-to-optical efficiency predicted
• Proposed multi-slab architecture should be scalable toat least 1 kJ generating ns pulses at up to 10 Hz– Limit to scaling is acceptable B-integral
• DiPOLE prototype amplifier shows very promising results– Installation of relay-imaging multi-pass should deliver 10 J @ 10 Hz
• Strong candidate pump technology for generating high energy, ns pulses at ~ 1 Hz for HELMHOLTZ-BEAMLINE
Thank you for your attention!
Any Questions?