1 / 23

P. D. Mason , S. Banerjee, K. Ertel, P. J. Phillips, C.Hernandez-Gomez, J. Collier

Diode Pumped Cryogenic High Energy Yb -Doped Ceramic YAG Amplifier for Ultra-High Intensity Applications. P. D. Mason , S. Banerjee, K. Ertel, P. J. Phillips, C.Hernandez-Gomez, J. Collier ICUIL 2010 Conference September 26 th to October 1 st 2010, Watkins Glen, NY, USA paul.mason@stfc.ac.uk

abiba
Download Presentation

P. D. Mason , S. Banerjee, K. Ertel, P. J. Phillips, C.Hernandez-Gomez, J. Collier

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Diode Pumped Cryogenic High EnergyYb-Doped Ceramic YAG Amplifier forUltra-High Intensity Applications P. D. Mason, S. Banerjee, K. Ertel, P. J. Phillips, C.Hernandez-Gomez, J. Collier ICUIL 2010 Conference September 26th to October 1st 2010, Watkins Glen, NY, USA paul.mason@stfc.ac.uk R1 2.62 Central Laser Facility STFC, Rutherford Appleton Laboratory, OX11 0QX, UK +44 (0)1235 778301

  2. Motivation • Next generation of high-energy PW-class lasers • Multi-Hz repetition rate • Multi-% wall-plug efficiency • Applications • Ultra-intense light-matter interactions • Particle acceleration • Intense X-ray generation • Inertial confinement fusion • High-energy DPSSL amplifiers needed • Pumping fs-OPCPA or Ti:S amplifiers • Drive laser for ICF BeamlineFacility

  3. Amplifier Design Considerations • Requirement • Pulses up to 1 kJ energy @ 10 Hz, few ns duration, overall > 10% • Gain Medium • Amplifier Geometry

  4. Amplifier Concept • Ceramic Yb:YAG gain medium (slabs) • Best compromise to meet requirements • Possibility of compound structures for ASE suppression • Distributed face-cooling by stream of cold He gas • Heat flow along beam direction • Low overall aspect ratio & high surface area • Coolant compatible with cryo operation • Operation at cryogenic temperatures • Reduced re-absorption, higher o-o efficiency • Increased gain cross-section • Better thermo-optical & thermo-mechanical properties • Graded doping profile • Reduced overall thickness (up to factor of ~2) • Lower B-integral • Equalised heat load for slabs

  5. Amplifier Parameters • Quasi-3 level model • 1D, time-dependent model • Spectral dependence (abs.) included • Assume Fmax = 5 J/cm2 forns pulses in YAG • Results • Optimum doping x length product  maximum storage efficiency ~ 50% • Optimum aspect ratio to ensure g0D  3  minimise risk of ASE • Highly scalable concept • Just need to hit correct aspect ratio & doping # Aperture / length

  6. Amplifier Design Parameters

  7. DiPOLE Prototype Cr4+ Pump2 x 2 cm² • Diode Pumped Optical Laser for Experiments • 10 to 20 Joule prototype laboratory test bed • 4 x co-sintered ceramic Yb:YAG slabs • Circular 55 mm diameter x 5 mm thick • Cr4+ cladding for ASE management • Two doping concentrations 1.1 & 2.0 at.% • Progress to date • Ceramic discs characterised • Amplifier head designed & built • CFD modelling of He gas flow • Pressure testing • Cryo-cooling system completed • Diode pump lasers being assembled • Lab. refit near completion 55 mm 35 mm Yb3+

  8. Ceramic Yb:YAG Discs • Transmission spectra • Uncoated, room temperature • Transmitted wavefront Fresnel limit ~84% PV 0.123 wave 1030 nm 940 nm

  9. Amplifier Head • CFD modelling • Predicted temperature gradient in Yb:YAG amplifier disc • Head layout Vacuum vessel 1.1% Uniform T across pumped region ~ 3K Pump 2 cm Pump 2.0% He flow He flow

  10. Cryo-cooling System Vacuum insulated transfer lines Helium cooling circuit Amplifierhead Cryostat

  11. Diode Pump Laser • Built by Consortium • Ingeneric: Opto-mechanical design & build • Amtron: Power supplies & control system • Jenoptic: Laser diode modules • Specifications • 2 pump units – left & right handed • 0 = 940 nm, FWHM < 6 nm • Peak power 20 kW • Pulse duration 0.2 to 1.2 ms • Pulse repetition rate variable 0.1 to 10 Hz • Other specs. independent of PRF

  12. Diode Pump Laser Spatial profiles (Modelled) • Beam profile specification • Uniform square profile • Steep profile edges • Low (<10°) symmetrical divergence • Demonstrated performance • Square beam shape • Low-level intensity modulations • Steep edge profiles • 20 kW peak output power • High confidence that other specifications will be demonstrated shortly Near Field Far Field Preliminary measurement

  13. Lab Layout LN2 tank Cryo-cooling system Optical tables Floor area ~30 m2 Amplifier

  14. Next Steps • Short-term (3 to 6 months) • Complete lab. refit • Install & test cryo-cooler & diode pump lasers • Characterise amplifier over range of temperature & flow conditions • Spectral measurements (absorption, fluorescence) • Thermo-optical distortions (aberrations, thermal lensing etc.) • Opto-mechanical stability • Small signal gain & ASE assessment • Long-term (6 to 12 months) • Specify and build front-end system • Shaped seed oscillator & regen. amplifier • Complete design of multi-pass extraction architecture (8 passes) • Amplify pulses • Demonstrate >10 J, 10 Hz, >25 % o-o efficiency

  15. Any Questions ?

  16. Yb-doped Materials

  17. Yb:YAG Energy Level Diagrams • Cryogenic cooling (175K) Quasi-3 Level 4 Level-like • Room temperature (300K) 2F5/2 2F5/2 Low quantum defect (QD)p/ las~ 91% Re-absorption loss 940 nm 1030 nm 940 nm 1030 nm Significantly reduced re-absorption loss f13=4.6% f13=0.64% 2F7/2 2F7/2 Yb3+ Yb3+

  18. Temperature Dependence Operating fluence T=175K Storage Efficiency (%) Small Signal Gain T=300K Pump Fluence (J/cm²)

  19. Doping Profile (1 kJ Amplifier)

  20. Pump Absorption Absorption + Pump Spectra Efficiency vs. lpump 175 K 300 K Pump, FWHM = 5nm 175 K, 10 kW/cm2 300 K, 20 kW/cm2

  21. Absorption Spectra Factor of 2 940 nm 1030 nm

  22. Ceramic YAG with Absorber Cladding Sample of Co-Sintered YAG (Konoshima) Reflection at Interface? Camera Laser Cr4+:YAG a b c ? Yb:YAG Yb:YAG Cr4+:YAG c b a Nothing!

  23. Beamline Efficiency Modelling • Beamline parameters • 2 amplifiers, 4-passes • 1% loss between slabs, 10% loss after each pass (reverser & extraction) • Losses in pump optics ignored Amp 2 Amp 1 Extraction Beam Transport Reverser 2 Reverser 1 Injection Injection Amp1 + 2 Reverser 1 Amp1 + 2 Reverser 2 Amp1 + 2 Reverser 1 Amp1 + 2 Extraction 17.4 % (distributed) 17.4 % (distributed) 17.4 % (distributed) Losses: 17.4 % (distributed) 10 % 10 % 10 % 10 %

More Related