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Key enabling technologies for compact high repetition rate Petawatt laser systems based on Titanium Sapphire amplifiers V.Moro, S.Branly, O.Casagrande, S.Laux, C.Radier, C. Simon-Boisson. Outline. Overview Contrast ratio Pump lasers Ti:Sa amplifiers design (ASE-parasitics & thermal)

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Outline

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  1. Key enabling technologies for compact high repetition rate Petawatt laser systems based on Titanium Sapphire amplifiersV.Moro, S.Branly, O.Casagrande, S.Laux, C.Radier, C. Simon-Boisson THALES Optronique ICUIL 2010, Watkins Glen

  2. Outline • Overview • Contrast ratio • Pump lasers • Ti:Sa amplifiers design (ASE-parasitics & thermal) • Conclusion & Perspectives THALES Optronique

  3. Commercial products Laboratory results Overview - Evolution of TW/PW Class Lasers • Thales holds a 18 years experience in the field of high energy and ultra short laser pulses. More than 200 Ti:Sa CPA systems installed in the world since 1992 1.3 PW – LBNL 1 PW – UNL 850 TW @ 28 J – JAEA 150 TW – UNL 100 TW @ 24 fs – LOA 25 TW – CRIEPI 15 TW – Tokyo U. 45 TW @ 1022 W/cm² – CUOS 10 TW – CEA 1 TW – KEK THALES Optronique

  4. Overview - Un.Nebraska –DIOCLES : 1 PW @ 0.1 Hz • Low repetition rate PW Class Laser : • Manufactured by successive upgrades since 2005. End of installation end 2010. • Laser room dimensions ~ 105 m². • Total pump power < 115 J (4 x ATLAS+ @ 25 J per laser). • Main specifications : • Peak Power > 1 PW. • Pulse Duration < 30 fs. • Energy > 30 J. • Rep. Rate 0.1 Hz. • ASE Level > 108 : 1. THALES Optronique

  5. Overview - LBNL–BELLA : 1.3 PW @ 1 Hz (1/2) • LBNL is seeking to demonstrate particle acceleration up to 10 GeV using laser-plasma interaction with a PW Class laser. It should take place in only a few cm space compared to 100’s of m with traditional accelerators. • THALES has been awarded in November 2009. The commissioning is expected end Spring 2012. • Laser room dimensions ~ 250 m². • Total pump power ~ 170 J (12 x GAIA HP @ 14 J each) THALES Optronique

  6. Overview - LBNL–BELLA – ALPHA 1/XS 1.3 PW • Energy(after COMPRESSOR) > 41 J • Pulse Duration < 30 fs • Peak Power > 1.3 PW • Repetition Rate 1 Hz • Wavelength 820 nm • Pump power > 170 J • Short Term Stability < 2.0 % rms over 10 min • Strehl Ratio > 0.9(using deformable mirror) • ASE Contrast > 1010 : 1 BELLA Laser @ LBNL THALES DSL Laser : ALPHA 1/XS 1.3 PW THALES Optronique

  7. Overview – Key enabling technologies • Large aperture Ti:Sa crystals • Compression gratings • Pump lasers • High damage threshold optics • Setups for improvement of contrast ratio • Removal of ASE & parasitics in amplification • Thermal management of Ti:Sa crystals • Spectral Bandwidth & Pulse duration optimisation • And more ….. THALES Optronique

  8. Contrast ratio improvement (1/2) • Since years, several techniques have been tested and implemented to improve the ASE Contrast such as Plasma mirrors, fast Pockels Cell, Saturable Absorber, … but with “relatively” low improvement. ⇒ ASE level was only ~ 108 : 1. • Through the PhD work of Aurélie Jullien (2003-2006) in collaboration between LOA (CNRS, Ecole Polytechnique and ENSTA) and THALES, a new technology have been developed XPW filter : • Increase of contrast ratio by 5 orders of magnitude • Increase of bandwidth by 3 ⇒ Reduction of Pulse Duration by 3. • No technical limitation. Limitation only coming from polarizers quality. THALES Optronique

  9. Contrast ratio improvement (2/2) • Since 2006, many laboratories have installed XPW technology in the FRONT END of their TW laser : LOA, LBNL, MBI, ILE-APOLLON etc… Following this thesis, THALES has developed a commercial product (2 crystals version in vacuum) which is now installed in several places : OSU, Texas University,… Contrast Ratio better than 1011:1 demonstrated at 45 TW output (instrument-limited measurement) • 2 crystals configuration* leads to better stability & better efficiency (25 to 30%) • An new version for ambient air operation with 2 BaF2 crystals is currently in development through a collaboration with LOA • Higher output energies are also investigated within a PhD work started in 2010 in collaboration with LOA CR of 1011:1 to 1012:1 are achievable with an optimised 2-crystals XPW *: patented THALES Optronique

  10. SAGA HP (2006) • Up to 1.6 J @ 532 nm. • 1 to 10 Hz operation. • 1 100 x 350 mm². • ATLAS+ (2008) • Up to 25 J @ 527 nm. • 0.1 Hz operation. • 2 500 x 1 000 mm². • Equiv to ~ 15 SAGA. • GAIA-R HP (2009) • Up to 14 J @ 532 nm. • 1 to 5 Hz operation. • 2 500 x 1 000 mm². • Equiv to ~ 9 SAGA. Pump lasers – Products overview • Total pump power available • The number of pump laser on a single Ti:Sa has to be limited for easiness of use, safety and reliability reasons. Typically between 8 and 10. • To increase total pump energy, one should increase energy per laser. Since 2000, THALES has developed a wide range of high energy pumps. THALES Optronique

  11. Pump lasers –ATLAS+ HP & GAIA specs chart THALES Optronique

  12. Pump lasers – ATLAS+ & GAIA features • Optimisation of extraction efficiency • Less pumping chambers • Reduced thermal loads & beam distortions • High beam quality & uniformity along the propagation inside & outside the laser • Shot-to-shot energy stability similar to diode-pumped lasers • High SHG efficiency when using LBO crystals • Routinely 60% for ATLAS+ and 70% for GAIA (compared to respectively 30-35% & 50-55% for other commercial lasers) • 83% SHG efficiency achieved in lab without temporal shaping • Evaluation of A/R coatings LIDT in cooperation w/ Cristal Laser, manufacturer of LBO: > 15 J/cm2 (multiple irradiations) THALES Optronique

  13. Pump lasers - GAIA HP measurements Depointing < 50 µrad (over 55000 measures) Beam profile @ 14J in the green @ 1 Hz Long term stability over 3 hours @ 1 Hz and 15 J @ 532 nm THALES Optronique

  14. Beam profile after 2.5m of propagation with 23mm diameter. Beam profile after 18m of propagation with 75mm diameter. Beam profile after 1.5m of propagation with 23mm diameter. Beam profile after 9m of propagation with 75mm diameter. F75mm F23mm GAIA-R HP 15m 25m 20m 30m 10m 5m f=-400mm f=+1200mm Ti:Sa position Beam profile after 0.5m of propagation with 23mm diameter. Beam profile after ~3m of propagation with 75mm diameter. Pump lasers – GAIA HP propagation The GAIA-R HP exhibits a very constant beam profile along propagation and does not require any image relay (no vacuum tube). THALES Optronique

  15. Pump lasers – New developments • New projects (APOLLON-10 PW in France & ELI at the European level) need pump lasers which much higher energy. • APOLLON requires 800J of green light for the 2 final TiSa amplifiers • Pump lasers demonstrating around 200J at rep-rate > 1 shot/min with very stringent specs on the spatial and temporal shapes (in order to maximize the efficiency) must be designed. • Thales Optronique is currently involved in the competitive dialog for the 200 J pump lasers of APOLLON (as well as Quantel & Continuum). • Modelling work has been performed in 2009. • Some parts of the laser will be breadboarded in 2010-2011 THALES Optronique

  16. ASE & Transverse lasing - Rationale • Energy extraction in high gain is limited by the onset of ASE & parasitic lasing (transverse lasing can occur in the high gain regions in case of air or water interface) • The transverse lasing threshold can be increased by using a melt of index matching fluid and absorber directly surrounding the crystal • TOSA has developed an optimised melt and a mechanical mount for the crystal while keeping an adequate thermal management of the crystal (confirmed by FEM modelling) • In order to further increase ASE and transverse lasing thresholds a time shifting technique (*) is applied to the pumping lasers (*): patented THALES Optronique

  17. Beam shaping Ti:Sa Cristal Dump CCD Camera Filters ASE & Transverse lasing - Experimental setup • Experimental setup: • A- The beam of a Gaïa laser has been shaped to an elliptic shape (2.3 cmx0.6cm) in order to illuminate a F30 mm Ti:Sa with a fluence of up to 5J/cm² at 532 nm. • B- The major axis of the beam was // to the axis of transverse lasing. • C- The criteria for detecting transverse lasing is hole burning on the fluorescence cut. • D- Experiment with no index matching, index matching with water and "perfect index matching + absorption" were carried out. THALES Optronique

  18. Fluorescence Higher pump fluence possible if asynchronous pumping is implemented Intensity (a.u.) ASE Threshold Transverse lasing Threshold Pump Fluence (J/cm²) ASE & Transverse lasing - experimental results THALES Optronique

  19. Conclusions & perspectives • An optimised 2-crystals XPW stage in the front end provides high values of the contrast ratio which are enough for most applications • Recent breakthrough in pump lasers have made possible operation at high energy and high rep rate at the same time what opens the way to 1 PW at 1 Hz and probably more in the near future • Combination of careful thermo-mechanical design and time shifting of the pump lasers allow a safe operation which prevent onset of ASE & transverse lasing and thermally-induced beam distortions. Ongoing R&D for scalability to higher rep rates. • There is ongoing R&D at Thales on other topics like for example STCPA (paper TO13 of C.Radier at that conference) • Multi-Petawatt and higher repetition rates could become commercially available within few years THALES Optronique

  20. THANK YOU FOR YOUR • ATTENTION THALES Optronique

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