Laser glass development at SCHOTT

1. Laser glass development at SCHOTT

2. SCHOTT has produced laser glass in Pennsylvania since about 1980 SCHOTT’s Duryea site has complete responsibility for laser glass research and development, manufacturing, and customer support for the SCHOTT Group worldwide Two developments of critical importance to the glass solid state laser community: Development of platinum particle free melting Development of continuous melting of phosphate laser glass Recent developments include: High repetition-rate laser glass: APG-1/APG-2 (>10 Hz). New broad-band phosphate and silicate laser glasses and higher-power repetition-rated phosphate glasses currently under development Laser glass production research and development at SCHOTT

3. SCHOTT production began with silicate glass for Shiva in 1977 Production since 1983 has been dominated glasses based by on phosphorous The spatial scale of our products has also increased over time Laser glass historical perspective - keeping pace with the needs of fusion research

4. The latest generation of high energy laser systems for ICF research (NIF, LMJ) demanded an unprecedented volume of laser glass to be produced over a limited manufacturing period while still meeting ambitious targets of internal quality and overall cost Development of continuous melting of phosphate laser glass Artist Rendition of National Ignition Facility (NIF) Laser

5. Starting materials would react with and alloy the platinum pot However, refractory materials such as SiO2 are also dissolved into the batch, leading to inhomogeneity in the glass Remelting of “cullet” glass in platinum avoids the alloying problem and makes high homogeneity glass possible Remelting cullet glass still allows the inclusion of Pt particles Traditional laser glass was produced in a two step process that includes remelting in a platinum crucible

6. Elimination of platinum inclusions increases laser damage threshold by 10X • In the absence of Pt inclusions, the damage threshold of laser glass optical components is now limited by the quality of the surface polish

7. Redeposited platinum vapor of spatial size >0.3m can damage on the next shot Below 0.3m, the heat is conducted into the glass Damage grows with successive shots above the damage threshold • Laser glass parts became unusable after only a few high power shots

8. The key to solving the Pt particle problem was to dissolve the particles into the glass structure as ionic Pt4+ • Platinum particles appear to be created at the start of the melt cycle • Dissolution is limited by diffusion of platinum away from the particle surface • Care must be taken to avoid the late arrival of Pt particles into the melt from condensed vapors

9. To meet schedule and cost targets NIF and LMJ required both a new glass and a new manufacturing process • The NIF laser alone required 3000 slabs (150 metric ton) over 3 years with the following specifications: • Index uniformity to <±0.000001 • Free of inclusions and bubbles larger than 100um • Residual hydroxyl content <100ppmw • Platinum particle free • Free of all detectable striae • Low 1054nm absorption of <.19% per cm thickness Beamlet eighteen liter rare earth doped phosphate glass amplifier slab

10. Batching Batching 1. Raw 1. Raw To Scrubber To Scrubber 5. Homogenizer 5. Homogenizer Material Material Exhaust Exhaust Process Control Process Control Lab Samples Lab Samples Continuous Continuous Monitoring All Monitoring All 4. Refiner 4. Refiner Properties Properties 2. Melter 2. Melter 3.Conditioner 3.Conditioner 8. Cut 8. Cut / / Inspect Inspect Melt and Form Melt and Form 6. Forming 6. Forming 7. Annealing 7. Annealing Lehr Lehr Meeting the laser glass requirements in terms of cost, quality, and rate of delivery for NIF demanded the development of an advanced manufacturing technology • Continuous melting runs 24 hours a day / 7 days per week • 100% Inspection, interferometry and laser damage testing

11. SCHOTT conceived, designed, and demonstrated the full scale continuous production line from 1994 to 1999 • Over 1400 laser slabs were first produced by the new continuous melting process in 2001 • All technical specifications and targets for the NIF were surpassed • 26% of slabs were essentially perfect, far exceeding overall specifications for residual water, platinum particles and homogeneity • Laser glass deliveries for the NIF and LMJ were completed in March 2004

12. Current laser glass research and development at SCHOTT • Ongoing $2.8M Production contract for discontinuous melting laser slabs and rods. • Awarded $2.5M for development of next-generation silicate and phosphate laser glasses are under development

13. Process Development – Summary • SCHOTT has been a major supplier of laser glass since 1980 • SCHOTT has also been active in the development of new manufacturing technology extending the operation range and lowering the cost of our products • This activity has created at SCHOTT further understanding on glass and supported the application of our other products into the marketplace • The two most critical developments in the last 20 years have been the availability of platinum particle free laser glasses and the continuous melting of phosphate laser glass • Our efforts in laser glass are industry recognized and promote our reputation as the lead supplier of optical materials for laser applications