In May, 1996, we demonstrated the production over a petawatt of peak power in the Nova/Petawatt Laser Facility, generating 620 J in {approximately} 430 fs. Results of the first focused irradiance tests, and recent deployment of a novel targeting system will be presented

Britten, J. A.

Brown, C. G.

Herman, S.

Homer, J.

Miller, J. L.

Pennington, D. M.

Perry, M. D.

Stuart, B. C.

Tietbohl, G.

Van Lue, J.

Yanovsky, V.

UNT Digital Library

.,UCRL-JC-127729PREPRINTThe Petawatt Laser and Target Irradiation System at LLNLD. M. Pennington, M. D. Perry, J. A. Britten, C. G. Brown, S. Herman,J. Homer, J. L. Miller, B. C. Stuart, G. Tietbohl, J. Van Lue, V. YanovskyThis paper was prepared for submittal to theUltrafast Optics 1997Monterey, CAAugust 4-7,1997DISCLAIMERThis document was prepared as an account of work sponsored by an agency ofthe United States Government. Neither the United States Government nor theUniversity of California nor any of theiremployees,makes any warranty, expressor implied, or assumes any legai fiability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any spe&c commeraal product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily amstitute orimply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California. The views and opinions of authorsexpressed herein do not neces@ly state or reflect those of the United StatesGovernment or the University of CaIifomia, and shiil not be used for advertisingor product endorsement purposes.THE PETAWATI’ LASER AND TARGETIRRADIATION SYSTEM AT LLNLD. M. Pennington, M. D. Perry, J. A. Britten, C. G. Brown, S. Herman,J. Homer, J. L. Miller, B. C. Stuart, G. Tietbohl, J. Van Lue, V. YanovskyLuser Program, Lawrence Livermore National Laboratory,PO Box 808, L-439, Livermore, CA 94550Telephone: (510) 423-9234, Telefa: (510) 422-5537e-mail: penningtonl @llnl.govABSTRACTIn May, 1996, we demonstrated the production over a petawatt of peak power in theNova/Petawatt Laser Facility, generating 620 J in -430 fs. Results of the first focusedirradiance tests, and recent deployment of a novel targeting system will be presented...-THE PETAWA’IT LASER AND TARGET IRRADIATION SYSTEM AT LLNLD. M. Pennington, M. D. Perry, J. A. Britten, C. G. Brown, S. Herman,J. Homer, J. L. Miller, B. C. Stuart, G. Tietbohl, J. Van Lue, V. YanovskyLuser Program, Luwrence Livermore National ikborato~,PO Box 808, L-439, Livermore, CA 94550Telephone: (510) 423-9234, Telefa: (510) 422-5537e-mail: penningtonl (i?llnl.govWe recently demonstrated the production of over a petawatt of peak power in theNova/Petawatt Laser Facility, generating 620 J in -430 fs. The Petawatt Laser Projectwas initiated to develop the capability to test the fast igniter concept] for inertialconfinement fusion (ICF), and to provide a unique capability in high energy densityphysics. The laser was designed to produce near kJ pulses with a pulse durationadjustable between 0.5 and 20 ps. At the shortest pulse lengths, this laser will produce >1021W/cm2 when focused at F/3.The laser system begins with a Tisapphire chirped pulse amplification system operating at1054 nm. The pulse is stretched to - 3 ns and is amplified up to 50 mJ in the titanium-sapphire section with minimal bandwidth narrowing. Further amplification in mixedphosphate glass rod amplifiers produces a speetrally-shaped 10 J pulse. This pulse isfhrther amplified up to the near kilojoule level by a series of disk amplifiers. Neardiffraction-limited beam quality is achieved by utilizing only the central 80% of the diskamplifiers and the use of adaptive optics to correct any residual thermal or pump inducedaberrations. Following amplification, the chirped nanosecond pulse is compressed by apair of large aperture diffraction gratings arranged in a single pass geometry. The pulselength can be adjusted easily from 0.43-20 by varying the length of the pulse stretcher.Pulse compression occurs in vacuum with a compressor throughput of 84%. Currently,the system produces nominally 600 J pulses for routine operation in a 46-cm beam.Expansion of the beam to 58-cm with the installation of 94-cm gratings will enable 1 kJoperation. Near field and focused irradiance, spectrum and autocorrelation are measuredon each shot using a transmission through a leaky mirror into a full aperture diagnosticstation.Target experiments with petawatt pulses will be possible either integrated with Nova 10-beam target chamber for fast ignition experiments, or in an independent target chamber forsingle beam experiments. For long pulse (-20 ps) experiments, the beam is focused by anon-axis parabolic mirror, which is protected from target debris by a full aperture debrisshield. For short pulse experiments, however, a conventional l-cm thick fhsed silicadebris shield would produce an accumulated nonlinear phase retardation of -28 radians,double-passed! To protect the parabola from line-of sight debris without incurring a largenonlinear phase retardation, a secondary “plasma mirror” is used in conjunction with theprimary parabola.2 For irradkmces >1014 W/cm2, short pulse radiation creates a criticaldensity plasma on the surface of a dielectric substrate, with a demonstrated reflectivity >90%. For incident pulses on the order of 500 fs, the plasma has insufficient time toundergo hydrodynamic expansion, producing a reflected wavefiont comparable to theoriginal optical surface. This novel targeting system will enable the production ofltrahigh contrast pulses, with an easily varied effective focal length by changing thecurvature of the secondary mirror.The first target experiments in the single beam chamber measured electron transport andheating in multilayer targets, as well as x-ray and neutron yield. Experiments wereperformed using the 20 ps pulse length required for fast ignition experiments, achieved1019W/cm2. Measurements of the focused irradiance demonstrated a focal spot roundfocal spot, approximately 15 pm in diameter. These results indicate that a focal irradianceof> 1021W/cm2 will be achievable with the Petawatt operated at 450 fs. Results of theshort pulse focused irradiance tests with the plasma mirror at 500 J in 450 fs will bepresented.References:1. M. Tabak, J. Hammer, M. E. Glinsky, W. L. Kruer, S. C. Wilks, J. Woodworth, E. M.Campbell, M.D. Perry, and R. J. Mason, “Ignition and high gain with ultra-powerfullasers;’ Phys. Pkwnas, vol. 1, pp. 1626-1634, 1994.2. M.D. Perry, V. Yanovsky, M. Feit, and A. Rubenchik, “Plasma mirrors:’ Phys.Plasmas, submitted, 1997.This work was performed under the auspices of the U.S. Department of Energy by theLawrence Livermore National Laboratory under Contract No. W-7405 -ENG-48Technical Information Department  • Lawrence Livermore National LaboratoryUniversity of California • Livermore, California  94551

Petawatt laser and target irradiation system at LLNL

Petawatt laser and target irradiation system at LLNL

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