Mark Tillack, John Pulsifer, Kevin Sequoia, Akachi Iroezi, Joel Hollingsworth Final Optic Fabrication, Testing and System Integration HAPL Project Meeting Oak Ridge, TN March 2006

1.Capabilities established for UV exposures, diagnosis and post-test examination 2.Scoping experiments quantified the importance of film thickness, grain structure, impurities and contaminants 3.Vendors were evaluated for fabrication of thick films by electroplating and evaporative coating, followed by diamond turning 4.Damage curves were obtained to 10 6 shots with 25-ns pulses at 248 nm. Initial results were encouraging. 5.To complete our studies of GIMM’s, we are improving our simulation fidelity, testing to end-of-life, fielding tests with 4” optics and performing component and system integration 6.We are also preparing to support the testing of multi-layer dielectrics Status of GIMM research at UCSD

1.Beam smoothing issues and improvements 2.Pulse slicing result, thermal comparison 3.Evaporative coatings vs. electroplating 4.Component and system integration Overview of Progress

Beam propagation of our Compex laser leads to profile nonuniformities at aperture90% “far field” Struggles with the Compex: Wavefront varies across beam Profile changes as it propagates Profile changes with gas age 4 days 25 days 42 days

Beam smoothing techniques were explored ~$20k Commercially available Large f-numbers available ~free 77% UV beam homogenizer Home-made smoothing system

A new laser (100-Hz, 700-mJ, LPX-Pro 210) reduces this problem, provides higher pulse energy and 10x the data rate

LPX profile variation with space (±1 cm at mirror location) 2 mm

LPX profile variation with time (at mirror location)

A Pockels cell now gives us 5-ns pulsewidth capability we retain 1/3 of the energy, but need only 5 J/cm 2 instead of 10 FastPulse 5046E (KD*P)

The temperature and gradient are now much closer to the Schmitt reference case Absorbed heat flux using fixed total energy Surface temperature (2x energy in Compex)

So where’s the data? Transmission through heavily- deuterated KD*P (KD 2 PO 4 ) is not what we expected at 248 nm We’re working with vendors to improve KD*P transmission, possibly switch to BBO * after 1200 shots(30-mm thickness) Or use the Compex as a front-end …

Electroplated aluminum was previously shown to withstand 5-10 J/cm 2 10 ppm Lifetime is limited by grain motion:

Evaporative coatings should produce better results due to smaller grains Schafer Corp. prepared 2” test samples: 100 µm evaporative coatings on Al-6061 substrate diamond-turned to 2 nm RMS, 15 nm PV

Initial data on evaporative coatings exhibits differences vs. electroplating Appears to be weak against rapid onset growth, strong against long-term growth Highly repeatable data!

GIMM’s are composed of an array of GIMMlets located 24 m from chamber center 347 cm 401 cm

The reference mirror is SiC composite or AlBeMet faceplates surrounding open cell foam or honeycomb structures 4” MER mirror, Al-coated SiC face sheet on SiC/SiC honeycomb Rohm & Haas uncoated CVD SiC w/ integrated cooling 4” Ultramet uncoated SiC facesheet on SiC foam Schafer lightweight optics, kg/m 2 Considerable industrial experience with Si, SiC, C-C and C-SiC composite mirrors Concerns: Al bonding and radiation-induced swelling

Choice of substrate depends on neutronics, thermomechanics, availability (R&D needs)… * “The alloy has desirable thermal and structural properties, but there is no heritage for its use as a mirror substrate” (

Remaining Goals for GIMM R&D Choose and demonstrate a coating-substrate combination – Finish specimen tests of evaporative coatings – Fabricate and test Al on C/Si and Al/Be composites Perform end-of-life testing – Solve the crystal absorption problem (pulse length) – Demonstrate no rep-rate effects exist Perform large-area testing – Obtain 4” specimens from vendors – Plan test campaigns at Mercury and Electra Develop prototype mirror – Develop designs – RFP’s to vendors