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A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Amplifier Paul Mason, Klaus Ertel, Saumyabrata Banerjee,

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Presentation on theme: "A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Amplifier Paul Mason, Klaus Ertel, Saumyabrata Banerjee,"— Presentation transcript:

1 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 5-9 th September 2011, Dresden, Germany STFC Rutherford Appleton Laboratory, Centre for Advanced Laser Technology and Applications R Central Laser Facility, OX11 0QX, UK +44 (0)

2 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 Beamline Facility HELMHOLTZ- BEAMLINE

3 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 potential Minimise number of diodes (cost) Available in large sizeHandle high energies Good thermo-mechanical propertiesHandle high average power Sufficient gain cross sectionEfficient energy extraction Low quantum defectIncreased efficiency & reduced heat load High surface-to-volume ratioEfficient cooling Low (overall) aspect ratioMinimise ASE Heat flow parallel to beamMinimise thermal lens

4 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

5 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 (g 0 D < 3) of ~1.5 –Extraction Extraction efficiency ~ 50% Thermal & fluid mechanics –Temperature distribution –Stress analysis –Optimised He flow conditions 50% 3.8 pump region Cr 4+ :YAG Yb:YAG

6 HiPER HiLASE / ELI Prototype DiPOLE Extractable energy~ 1 kJ~ 100 J~ 10 J Aperture 14 x 14 cm 200 cm 2 5 x 5 cm 25 cm 2 2 x 2 cm 4 cm 2 Aspect ratio No. of slabs1064 Slab thickness1 cm0.7 cm0.5 cm No. of doping levels532 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 cm 200 cm 2 5 x 5 cm 25 cm 2 Aspect ratio No. of slabs106 Slab thickness1 cm0.7 cm No. of doping levels53 Average doping level 0.33 at.%0.79 at.% Scalable Design

7 DiPOLE Prototype Amplifier Design sized for ~ 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 Cr 4+ Yb 3+ Ceramic YAG disk with absorber cladding Diode pump laser

8 4 x co-sintered ceramic Yb:YAG disks –Circular 55 mm diameter x 5 mm thick –Cr 4+ absorbing cladding –Two doping concentrations (1.1 & 2.0 at.%) Optical Gain Material Cr 4+ Yb mm 55 mm Pump 2 x 2 cm² PV wave Fresnel limit ~84% 940 nm 1030 nm

9 Amplifier Head Design SchematicCFD modelling Uniform  T across pumped region ~ 3K He flow 40 m 3 /hr ~ bar, 175 K Pump Vacuum Disks pressure windows vacuum windows

10 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 absorption 175K Measured 20 mm

11 DiPOLE Laboratory Cryo-cooling system 2 x 20 kW diode pump lasers Amplifier head

12 Front-end Injection Seed Free-space diode-pumped MOPA design –Built by Mathias Siebold’s 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 booster amplifier –6 or 8 pass configuration –Output energy ~ 100 mJ nsec oscillator Booster pump diode Amplifier crystal 100 mJ output Polarisation switching waveplate x3 or x4

13 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 Pump Seed Amplified beam

14 Spatial Beam 100K, 1 Hz E = Hz Gain  8 Gain  6

15 Pulse Energy v. Pump Pulse Duration 3 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

16 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 to at 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 Hz Strong candidate pump technology for generating high energy, ns pulses at ~ 1 Hz for HELMHOLTZ-BEAMLINE

17 Thank you for your attention! Any Questions?


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