SCHOTT – Ultra Low Expansion Glass Ceramic ZERODUR® Improvements in Properties, Understanding and Production
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SCHOTT – Ultra low expansion glass ceramic ZERODUR® Improvements in properties, understanding and production MPI für Astronomie, Heidelberg Astro Tech Talk 30.1.2015 Peter Hartmann SCHOTT AG Advanced Optics 2 What is ZERODUR®? 2 Advanced Optics 3 1957 Glass Ceramic discovered by Donald S. Stookey (Corning) From mishap during development of light sensitive glass Furnace became much too hot. Advanced Optics 4 ZERODUR®– Work of Two Pioneers The first 4 m Zerodur Mirror 3,6 m Telescope Calar Alto Hans Elsässer Jürgen MPI Astronomy Petzold Initiator and SCHOTT Customer Developer of glass ceramics 1973 Cast of the first 4 m glass ceramic mirror blank for the Max-Planck-Insitute for Astronomy Heidelberg Germany Advanced Optics 5 ZERODUR® - Zero Expansion Glass Ceramic Zerodur is a Li-Al-Si glass ceramic a composite of 70 – 78 vol-% microcrystallites embedded in a glass phase Size and number of the negative CTE microcrystallites are adjusted to achieve a net zero thermal expansion Scanning microscope image of Zerodur microcrystallites Size: 30 – 50 nm Advanced Optics 6 ZERODUR® is molten like Optical Glass Therefore it is . Extremely homogeneous . Isotropic down to sub microscopic scale Free from rings, layers Seams, flaws, pores . Highly polishable . In transmission inspectable no surprises . Highly reproducible 1.5 m Blank with outstanding in all properties homogeneity and striae quality Advanced Optics 7 Coefficient of thermal expansion CTE 7 Advanced Optics 8 Coefficient of Thermal Expansion (CTE) Narrower tolerances have been added CTE Absolute Values New Class CTE [1/K] Class CTE [1/K] 2 ± 0.10 · 10-6 0 Special ± 0.010 · 10-6 1 ± 0.05 · 10-6 0 Extreme ± 0.007 · 10-6 0 ± 0.02 · 10-6 Taylored Adapted to specific temperature profile Advanced Optics ZERODUR® TAILORED 9 The CTE at a specific temperature T might differ from the mean value determined by the slope of the expansion between 0° and 50°C. CTE(T) CTE(0,50)=0.015 ppm/K 9 Advanced Optics 10 Structural relaxation can be calculated Length change depends on temperature and temperature change rates. Physical model capable to predict the thermal expansion at low temperature change rates. l / l vk Advanced Optics 11 ZERODUR® TAYLORED allows adjustment of thermal expansion to given temperature profile For extreme requirements small expansion lagging of ZERODUR may be compensated on the basis of a calculation model Temperature Profile Model Provision of material with minimum thermal expansion ZERODUR® TAILORED ZERODUR® EXTREME Temperature 11 Advanced Optics 12 ZERODUR® TAILORED optimized for 22°C shows smallest CTE variation between -50°C and +100°C CTE [ppb/K] atCTE [ppb/K] 100°C CTE data generated at SCHOTT dilatometer during heating from -50°C to +100°C 12 Advanced Optics ZERODUR® TAILORED 13 ZERODUR® TAILORED CRYO: very low thermal expansion over a wide temperature range (250K to 70K). New ZERODUR® 0,3 CTE(T) cryo 0,2 data* in 0,1 comparison with 0,0 results published in earlier papers -0,1 . ZERODUR® -0,2 TAILORED -0,3 CRYO: is -0,4 Z Roberts, 1982 optimized for low Z-1 Collocott, 1991 CTE [ppm/K] -0,5 Z-2 Collocott, 1991 temperature Z Burge, 1999 -0,6 ZERODUR sample 1 applications. ZERODUR sample 2 -0,7 ZERODUR TAILORED CRYO -0,8 0 50 100 150 200 250 300 T [K] * ZERODUR® sample 1, sample 2 and TAILORED CRYO measured by the PTB (Physikalisch 13 Technische Bundesanstalt, national standardization laboratory 2013/2014) Advanced Optics 14 CTE Measurement Push rod dilatometer Interferometric measurement head Sample size 100 x 6 x 6 mm CTE Accuracy Repro (95%) (0°-50°C) [ppb K-1] [ppb K-1] Standard 10 5 Improved 6.2 1.2 Advanced Optics 15 Absolute CTE values of 42 Segments lie fairly well in tolerance 42 x 2 m segments for 10 m GRANTECAN Mirror Tolerance ± 0.05 +10-6 1/K Advanced Optics 16 Coefficient of thermal expansion CTE Homogeneity 16 Advanced Optics 17 CTE Homogeneity is highly repeatable Advanced Optics 18 CTE Homogeneity is highly repeatable - as statistics of more than 200 mirror blanks in sizes 1 – 2 m show 95,5 % of 95,5 % of CTE Repeatability Measurement (0,005) Values (0,007) Data from projects Keck I + II, GRANTECAN, HET Largest part of statistical variation comes from measurement repeatability variations Advanced Optics 19 CTE-Homogeneity of two 1.5 m x 0.35 m disks 1554 mm . Highly resolved with 90 + 21 samples . Standard blank 30 mm thick disc no special selection 90 samples 345 . Measured with best mm reproduction accuracy Vertical cut off: 21 samples Advanced Optics 20 CTE Homogeneity of two 1.5 m ZERODUR® disks Blank 1, 2006 Blank 2, 2008 Blank 1 Blank 2 Mean CTE (0°C, 50°C) [ppb K-1] 42.4 39.9 Homogeneity (p-v) [ppb K-1]6.43.8 Axial gradient (mean) [ppb K-1 mm-1 ] < 0.02 < 0.01 Advanced Optics 21 Excellent CTE homogeneity of a 1.2 m x 1.2 m rectangular 5 ppb/K p-v Small scale homogeneity 21 (x) and 14 (y) samples 4 ppb/K 3 ppb/K 110 x 100 mm 27 150 x 100 mm 14 9 8 3 2 000 0 0 -5-4 -3 -2 -1 0 1342 5 64 samples CTE differences in ppb/K of relative to mean CTE Reproducibility: ± 1.2 ppb/K (95% CB) Advanced Optics 22 Outstanding CTE Homogeneity of a 4m Mirror Blank 36 Samples Mean value: 54 ppb/K MP _4 Homogeneity: 8 ppb/K (!) MP _5 MP _3 Axial gradient: 2 ppb/K (!) MP _6 MP _2 MP _14 MP _15 MP _13 MP _7 MP _1 MP _16 0° - mark at the blank MP _18 MP _8 MP _17 MP _12 MP _9 MP _11 MP _10 Decke (Top) MP T7 MP T16 MP T13 MP T1 MP B7 MP B1 MP B16 MP B13 Boden (Bottom) not to scale Project ARIES Raw boule with virtual single blank Advanced Optics 23 DKIST Daniel K. Inouye Solar Telescope (formerly ATST) CTE Mean value and Homogeneity are excellent Top view CTE Temperature Interval 5°C / 35 °C 0°C / 50 °C Side view Mean 6 ppb/K 0 ppb/K PV 6 ppb/K 3 ppb/K Advanced Optics ZERODUR® TAILORED 24 The CTE values of the 6 most recently produced 4 m class ZERODUR® blanks show outstanding results in CTE homogeneity. CTE (0°; 50°) absolute CTE (0°; 50°) Sam Dimension -ple value homogeneity [ppb / K] [ppb / K] Specificatio Year [mm] # Specification Achieved Achieved n 2003 4100 x 171 18 +/- 50 66 20 18* 2005 3610 x 370 12 +/- 100 80 30 25* 2009 3700 x 163 36 +/- 150 54 40 9 2010 3400 x 180 12 +/- 100 42 30 5 2012 4250 x 350 16 +/- 30 60 40 5 2013 4250 x 350 16 +/- 30 0 40 3 * Measurement performed with older dilatometer 24 Advanced Optics 25 ZERODUR® Optical Homogeneity Ø 360 (Ap.: 226) mm x 63 mm PV: 9 × 10-7 RMS: 1,7 × 10-7 Class H5 Exceptional homogeneity of selected disk Advanced Optics 26 Material Homogeneity Material Properties 26 Advanced Optics 27 Extremely low bubble content is typical for ZERODUR® Bubbles Mapping Example of a 4 m blank Number of inclusions 0.1 - 0.5 mm 12 Number of inclusions 0.5 mm - 1.0 mm 8 Bubbles 1.0 mm 11 Max. diameter 2.7 mm 31 bubbles in the range of 0.1 – 2.7 mm in ca. 3000 kg! Advanced Optics 28 Very low striae is a heritage of optical glass production process Striae are refractive index variations within short ranges 0.1 – 1 mm SCHOTT has delivered several selected 2 m blanks with striae quality equivalent to best optical glass 1.5 m Blank with outstanding homogeneity and striae quality Advanced Optics 29 Stress birefringence statistics of 42 2 m diam. blanks for GRANTECAN 10 m mirror show stress below 0.1 MPa Tolerance: - 10 nm/cm 3 nm/cm corresponds to a stress of 0.1 MPa Negative values: Compressive stress Advanced Optics 30 Variation in Density reflects measurement uncertainty Data based on > 80 measurement within 5 years Advanced Optics 31 ZERODUR®: Polishability Zerodur can be polished to a very low residual roughness. X-Ray satellite optics: CHANDRA: 0.2 nm rms Extreme UV Microlithography EUVL: 0.15 nm rms after polishing under production conditions by Carl Zeiss Advanced Optics ZERODUR® Radiation Behavior 3232 ZERODUR®: Resistance against ionizing radiation is high Dose vs. Compaction for Zerodur -2 10 -3 First analyses 10 overestimated effect -4 by factor > 10 10 -5 10 Linear Compaction Linear -6 10 Revised equation = 2.63 x 10-8 D0.5 -7 10 2 3 4 5 6 7 8 10 10 10 10 10 10 10 Dose (Gy) Advanced Optics ZERODUR® Radiation Behavior 33 Hubble and Chandra show excellent performance up to now this holds for many more space borne telescopes … Hubble Space Telescope Orbit: LEO Deployment: April 1990 Lifetime: > 20 years Secondary Mirror Material: ZERODUR® M2 Diameter: 300 mm Chandra X Ray Telescope Orbit: MEO Deployment: July 1999 Lifetime: > 14 years Wolter Mirror Material: ZERODUR® Mirror Diameter / Length: 800 mm / 600 to 1200 mm Determine cumulated dose considering geometry and shielding Real life proof of ZERODUR®‘s performance 33 Advanced Optics 34 Bending strength 34 Advanced Optics 35 ZERODUR® Bending strength – New approach proves capability to endure high mechanical loads . Generally ZERODUR® is stronger than glasses . Strength is mainly determined by depth of micro cracks in its surface . Much larger data sets are available now . Ground surfaces lie higher than 40 MPa Etched surfaces higher than 100 MPa .