PREPARED BY: I. Miller DATE: 2004 May 23 CO-OWNERS REVISED DATE OF ISSUE/CHANGED PAGES

Transcription

1 Page 1 of 30 LIGHTMACHINERY TEST REPORT LQT TITLE: HMI Michelson Interferometer Test Report Serial Number 2 - Narrowband FSR INSTRUCTION OWNER HMI Project Manager PREPARED BY: I. Miller DATE: 2004 May 23 CO-OWNERS APPROVED BY I MILLER QUALITY ASSURANCE: R. Weeks REVISED DATE OF ISSUE/CHANGED PAGES REVISION RELEASE DATE CHANGED PAGES/NOTES A 2005 Feb 19 Initial release B 2005 May 2 Add silver data, material data, transmission calculations,reformated C 2005 May 2 Add coating witness table D 2006 Feb 2 Corrected error in specification table, spatial and angular variations, changed sign of field widening data to be consistsent with HMI 3 and 4 Note: All documentation is subject to change, and therefore you must check the company data base for the current Document Revision.

2 Page 2 of 30 Table of Contents 1.0 PURPOSE and SCOPE DOCUMENTATION TEST RESULTS...6 PERFORMANCE SUMMARY... 6 FREE SPECTRAL RANGE (3.1)... 7 TRANSMISSION AND CONTRAST (3.2)... 8 PVA POLARIZER UNIFORMITY... 9 CLEAR APERTURE (3.3) BEAM ORTHOGONALITY (3.4) SPATIAL VARIATIONS OVER THE APERTURE (3.5) ANGULAR VARIATIONS OVER THE APERTURE (3.6) THIN FILM BEAM SPLITTER COATING TEMPERATURE DEPENDENCE (3.7) WAVEFRONT ERROR (3.8) SURFACE FLATNESS MEASUREMENTS ANTIREFLECTION COATINGS (3.9) SILVER COATINGS SURFACE QUALITY (3.10) CEMENT (3.11) ASSEMBLY DIMENSIONS AND IDENTIFICATION (3.12) MATERIAL CERTIFICATES, PROCESS CERTIFICATIONS List of Coating Witness Samples...29

3 List of Figures LQT , Rev D Page 3 of 30 FIGURE 1: NARROW BAND MICHELSON (FSR NM), COMPLETE. KAPTON TAPE IS WRAPPED ON THE VACUUM ARM TO PROTECT THE VACUUM GLASS INTERFACES FIGURE 2: NARROW BAND MICHELSON AND MATCHING WIDE BAND MICHELSON (S/N 1) 5 FIGURE 3: CONTRAST MEASURED AFTER SILVERING OF END MIRRORS... 8 FIGURE 4: POLARIZER UNIFORMITY (CLOSED)... 9 FIGURE 5: POLARIZER UNIFORMITY (OPEN) FIGURE 6: THIN FILM POLARIZER T S SPATIAL UNIFORMITY FIGURE 7: PHASE VARIATION OVER APERTURE BEFORE SILVERING END MIRRORS12 FIGURE 8: PHASE VARIATION OVER APERTURE AFTER SILVERING END MIRRORS13 FIGURE 9: MICHELSON PHASE VARIATION VS. EXTERNAL ANGLE OF INCIDENCE 14 FIGURE 10: THIN FILM POLARIZER T S, VS. ANGLE IN SAGITTAL PLANE FIGURE 11: THIN FILM POLARIZER TP VS. SAGITTAL ANGLE FIGURE 12: TRANSMITTED WAVEFRONT ERROR, 0.11Λ PEAK-TO-VALLEY, POWER SUBTRACTED 17 FIGURE 13: SOLID ARM WAVE PLATE EXTERNAL SURFACE FIGURE FIGURE 14: VACUUM ARM WAVE PLATE EXTERNAL SURFACE FIGURE FIGURE 15: INTERFEROGRAM OF CUBE SURFACE FACING VACUUM ARM FIGURE 16: MEASURED REFLECTIVITY OF AR FIGURE 17: MEASURED REFLECTIVITY OF AR FIGURE 18: MEASURED REFLECTIVITY OF AR FIGURE 19: MEASURED REFLECTIVITY OF AR FIGURE 20: SILVER REFLECTOR MEASUREMENT (SHOWS ALL FOUR MIRRORS FOR HMI 1 AND HMI 2 22 FIGURE 21: INPUT/OUTPUT WAVE PLATE THICKNESS MAP FIGURE 22: VACUUM ARM WAVE PLATE THICKNESS MAP FIGURE 23: SOLID ARM WAVE PLATE THICKNESS MAP FIGURE 24: MATERIAL CERTIFICATE FOR 35 MM THICK OHARA BSL7Y GLASS FIGURE 25: MATERIAL CERTIFICATE FOR 50 MM THICK OHARA BSL7Y GLASS... 28

4 Page 4 of 30 HMI MICHELSON TEST REPORT 1.0 PURPOSE and SCOPE This test report includes detailed measurements of the components and the final performance of the narrowband HMI Michelson interferometer, Serial Number 2. The Lockheed Martin part number is H This report details the key measurements for the completed Michelson and subassemblies but does not include all measurements made in fabrication of the Michelson interferometer. This document encompasses the requirements of SDRL 05 and SDRL 06 as described in the statement of work 2H DOCUMENTATION Reference Documents 1. LightMachinery Filing cabinet M50 (QA Manager C Drive), Project binder 2. Specification for the Helioseismic & Magnetic Imager (HMI) Michelson Interferometer Assemblies. 2H00024 Rev A, 16 October 2003 Lockheed Martin Space Systems Company 3. Statement of Work for the Helioseismic & Magnetic Imager (HMI) Michelson Interferometer Assemblies. 2H00025 Rev A, 17 October 2003 Lockheed Martin Space Systems Company 4. HMI Michelson Fabrication Plan. D-OP LightMachinery Inc. Reference drawings: 1. D-OP HMI Fabrication process 2. D-OP HMI beam splitter cube 3. D-OP HMI polarization configuration

5 Page 5 of 30 Figure 1: Narrow band Michelson (FSR nm), complete. Kapton tape is wrapped on the vacuum arm to protect the vacuum glass interfaces. Figure 2: Narrow band Michelson and matching wide band Michelson (s/n 1)

6 Page 6 of TEST RESULTS This document describes tests and measurements performed on the components and completed HMI Michelson assembly. In this section, requirements for the completed Michelsons are referenced from 2H00024 with the section number from that document. Specific test procedures are described in the test plan LQI Performance summary A summary of the Michelson performance is presented in the table below. More detailed results for each measurement are in later sections. PCA 74 records the variances for this instrument. Description Specification Measurement Comment Free Spectral Range nm ±5% nm <0.1%, OK (3.1) Ratio of wide band to 2.00 ±1% %, OK narrow band free spectral range (3.1) Contrast (3.2) >95% 97% average OK Transmission (3.2) >80% >82% OK Clear aperture (3.3) 32 mm 34 mm OK Beam orthogonality ±15 arc seconds 2.5 arc seconds OK (3.4) Surface normals in < 1.0 arc second 2.0 arc second variance plane (3.4) deviation maximum deviation Spatial variations over λ 0 variations ± nm variance the aperture (3.5) Angular variations over the aperture (3.6) Temperature dependence (3.7) Wavefront error (3.8) Antireflection coatings (3.9) Surface quality (3.10) Cement (3.11) Assembly dimensions (3.12) < ± nm λ 0 variations < ± nm for rays within 3 of normal incidence ± nm OK d λ 0 /dt < nm/ C 0.84 pm/ C OK <0.05 wave 0.11 wave variance peak-valley peak-valley R<0.2% R<0.1% OK Optical surface scratch-dig or better Cement thickness <15 µm, visual inspection Better than Cement thickness < 15 µm, free from bubbles inspected OK OK OK

7 Page 7 of 30 Free spectral range (3.1) The target value for the free spectral range of the wide band Michelson is nm. The free spectral range calculated from measured Michelson properties is nm. The table below shows the measured component thicknesses and the calculated free spectral range. The ratio of the free spectral range of this instrument has been calculated relative to that of the matching narrow band instrument. The ratio is within 0.3% of the specification target. Measurement Solid arm length, before final reduction Solid arm wave plate thickness Reduction of solid arm prior to final assembly Finished solid arm thickness Net glass path difference between solid arm and vacuum arm Wave plate/ solid arm cement thickness Vacuum arm length Vacuum arm wave plate thickness Wave plate/ vacuum arm cement layer Refractive index of BSL7Y glass dn/dλ Calculated FSR Value mm mm 48 µm mm mm Norland 61, mm mm mm Norland 65, mm (from Ohara material certificate) /µm nm Ratio of wide band FSR to narrow band FSR <0.1% deviation is within 5% specification limit 0.3% deviation is within 1% specification

8 Page 8 of 30 Transmission and contrast (3.2) Contrast was measured with a nm collimated laser beam by comparing the maximum and minimum transmission levels as an external polarizer was rotated. Figure 1 shows the measured contrast over the instrument aperture. The average contrast is approximately 97%, compared to the specified minimum value of 95%. The laser has a gaussian intensity profile which degrades the signal to noise ratio at the edge of the Michelson aperture. Figure 3: Contrast measured after silvering of end mirrors Instrument transmission is calculated from two separate measurements: the measured transmission of the input/output polarizer and the measured reflectivity of the silver end mirrors. An allowance has also been made for misalignment of the wave plates and polarizer, based on their predicted alignment accuracy. The following table shows both the transmission and contrast data. Measurement Value Specification comment Silver mirror reflectivity >96.5% 95% Polarizer transmission 90% Transmission (3.2) >80% >82% OK Contrast 98% average 95% OK

9 Page 9 of 30 PVA Polarizer Uniformity The input/output polarizer uniformity was measured after AR coating one side. The data have shown are corrected for the 4% reflectance from the uncoated side. The average open transmission is 89.9% at nm. The average closed transmission is 0.067% at nm. Polarizer uniformity, closed, 3.8 mm grid S9 S8 S7 S S5 S4 S3 S2 S Figure 4: Polarizer uniformity (closed)

10 Page 10 of 30 Polarizer uniformity, open, uncoated, normalized to 100% transmission S9 S8 S S6 S5 S4 S3 S2 S Figure 5: Polarizer uniformity (open) Clear aperture (3.3) The clear aperture is 34 mm, limited by the AR coatings on the vacuum arm. Beam Orthogonality (3.4) The cube faces are made square to 1 arc second. After cementing, all external faces were measured to be within 2.0 seconds of perpendicular relative to their respective faces. Spatial variations over the aperture (3.5) Beamsplitter coating uniformity is shown in the plot below

11 Page 11 of 30 HMI Cube 05, Ts normal incidence S23 S22 S21 S20 S19 S18 S17 S16 S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 23 S Figure 6: Thin film polarizer T s spatial uniformity Data shown below were taken with phase averaging over a 0.3 mm x 0.3 mm pixel. The measured λ 0 variation is ± nm peak-valley compared to the specification of ±0.001 nm. Standard deviation (single sided) for the λ 0 variation is nm. Approximately 20% of the total phase error is due to wedge in the assembly.

12 Page 12 of 30 Figure 7: Phase variation over aperture before silvering end mirrors

13 Page 13 of 30 Figure 8: Phase variation over aperture after silvering end mirrors

14 Page 14 of 30 Angular variations over the aperture (3.6) The change in λ 0 with incident angle was measured at the center of the interferometer field. The variation in phase corresponds to a λ 0 variation of ± nm, compared to the specification of ±0.001 nm. The chart below shows the phase vs. angle data corrected for mode hops in the measurement laser and gradual drift. HM I 2 Phase vs. angle of incidence, corrected for HeNe drift and mode hops, sign convention 50 corrected sagittal phase corrected tangential phase Michelson phase (degrees) angle of incidence (external, degrees) Figure 9: Michelson phase variation vs. external angle of incidence

15 Page 15 of 30 Thin Film Beam Splitter Coating Ts with different sagittal angle in the wavelength range of 600 to 650 nm 42 deg sag 43 deg sag 44 deg sag 45 deg sag 46 deg sag 47 deg sag 48 deg sag Figure 10: Thin film polarizer T s, vs. angle in sagittal plane

16 Page 16 of 30 Tp with different sagittal angle Tp deg sag deg sag 44 deg sag deg sag 46 deg sag deg sag 48 deg sag Wavelength (nm) Figure 11: Thin film polarizer Tp vs. sagittal angle Temperature dependence (3.7) The temperature dependence of the Michelson was not measured. Based on measurements made on the engineering test unit, the temperature dependence is predicted to be dλ 0 /dt = 0.84 pm/ C. This change is less than the maximum permissible drift of 1 pm/ C.

17 Page 17 of 30 Wavefront error (3.8) The total wavefront error measured on the Zygo interferometer is 0.11λ peak to valley, after subtracting power, compared to the specified value of 0.05 λ. The figure below shows the transmitted wavefront error. Figure 12: Transmitted wavefront error, 0.11λ peak-to-valley, power subtracted

18 Page 18 of 30 Surface Flatness Measurements Figure 13: Solid arm wave plate external surface figure Figure 14: Vacuum arm wave plate external surface figure

19 Page 19 of 30 Figure 15: Interferogram of cube surface facing vacuum arm Antireflection coatings (3.9) Vacuum facing surfaces shall be antireflection coated to R < 0.2 % at nm over the central 35 mm diameter at angles from 0 to 5 from the surface normal. A witness from each anti-reflection coating run will be measured to ensure that the reflectance is less than 0.2%. The coating aperture for the anti-reflection coatings on the vacuum arm will have a nominal aperture of 34 mm to allow clearance relative to the vacuum spacer inside diameter of 35 mm. The spatial uniformity of at least one antireflection coating will be tested on the spectrometer system. Coating location Coating ID Notes AR on vacuum arm AR % R at nm wave plate AR on input/output AR 2 <0.1% R at nm wave plate AR on beam splitter AR % R at nm cube (facing vacuum arm) AR on polarizer AR % R at nm

20 Page 20 of 30 Figure 16: Measured reflectivity of AR 1 Figure 17: Measured reflectivity of AR 2

21 Page 21 of 30 Figure 18: Measured reflectivity of AR 3 Figure 19: Measured reflectivity of AR 4

22 Page 22 of 30 Silver Coatings The measured reflectivity of the silver coatings on the solid and vacuum arms is greater than 96.5%. The figure below shows the reflectivity of the four coatings applied to HMI 1 and HMI 2. Figure 20: Silver reflector measurement (shows all four mirrors for HMI 1 and HMI 2

23 Page 23 of 30 Surface quality (3.10) All of the optical surfaces of the interferometer are better than the specified scratch dig specification. Cement (3.11) The following table shows the type of cement used for each interface, and the lot code for the cement. Interface Cement Lot, expiry BSL7Y BSL7Y beam splitter Norland , 2004 Oct 3 BSL7Y crystal quartz Norland , 2004 Oct 3 CaF 2 BSL7Y (wave plate) Norland , 2005 July 12 BSL7Y PVA polarizer Norland 65 Cemented by Lockheed Martin BSL7Y polarizer BSL7Y cube Norland , 2005 May 14 BSL7Y input/output wave plate BSL7Y cube Norland , 2005 May 14 BSL7Y wave plate BSL7Y solid arm Norland , 2005 May 14 BSL7Y solid arm BSL7Y cube Norland , 2005 Sep 23 CaF 2 BSL7Y cube Norland , 2005 Sep 23 This table records the parallelism of the cemented components to the surfaces of the cube. Michelson face Measured parallelism between optic and cube fringes Wedge (arc seconds) Polarizer Input/output wave plate Vacuum arm Solid arm

24 Page 24 of 30 Assembly dimensions and identification (3.12) Overall Dimensions Dimension Measured value (measured in inches, converted to mm) X (wave plate to vacuum arm) Y (polarizer to solid arm) Specification limits mm <68.0 mm mm <70.0 mm Measured with Mitutoyo 3 micrometer , sn Checked with gauge block prior to measurements Z (height) mm 45.0±0.1 mm Mitutoyo 2 micrometer , sn Checked with gauge block prior to measurements Cube dimensions Dimension Measured value Measured with X mm Mitutoyo 2 micrometer 103- Y mm 136, sn Checked with gauge block prior to Z mm measurements Wave Plates Location Serial Number Thickness Maximum error Input/Output # mm λ/600 Vacuum arm # mm λ/450 Solid arm # mm λ/450

25 Page 25 of 30 Wave Plate Thickness Measurements Figure 21: Input/Output wave plate thickness map

26 Page 26 of 30 Figure 22: Vacuum arm wave plate thickness map

27 Page 27 of 30 Figure 23: Solid arm wave plate thickness map

28 Page 28 of 30 Material Certificates, Process Certifications All of the glass used in the HMI Michelson is from the same melt of Ohara BSL7Y glass material cerfificates attached. The wave plate sandwiches and solid arms were made from the 50 mm thick material, while the beam splitters were made from 35 mm thick material. The refractive index deltas are multiplied by 10 5 on the melt data sheets. Figure 24: Material certificate for 35 mm thick Ohara BSL7Y glass Figure 25: Material certificate for 50 mm thick Ohara BSL7Y glass

29 Page 29 of 30 The crystal quartz used in this instrument was supplied by Sawyer Research. The material code is SP The calcium fluoride spacers were fabricated from material supplied by Corning. The material was cut with the <111> crystal axis parallel to the optic axis of the instrument. The material code for the calcium fluoride is The PVA polarizer was assembled from BSL7Y blanks provided by LightMachinery, and PVA polarizer film provided by Lockheed Martin. Assembly of the polarizer sandwiches was performed by Lockheed Martin. AR coatings were applied to our specification CT Silver coatings were applied to our specification CT The polarizing beam splitter coating was applied by Iridian Spectral technologies; their run number #ds-bv b000 bxfs727a. 4.0 List of Coating Witness Samples The following table lists coating witness for all of the coating runs used in fabricating HMI 1 and HMI 2. Coating Witness Identification Polarizing beam splitter July 04 Iridian HMI B/S AR 1 Dec 8/04 AR on B/S + WP #12, #14 AR 2 BSL7Y Lockheed AR witness WP #10, #15 Polarizer Dec 15/04 AR 3 BSL7Y witness for vac arm of cube #2 Feb 23/05 AR 4 BSL7Y witness Mar 1/05 on reworked polarizer/cube HMI 1 solid arm BSL7Y silver witness for mm arm HMI 1 vacuum arm BSL7Y silver witness mm arm HMI 2 solid arm BSL7Y silver witness for mm arm HMI 2 vacuum arm BSL7Y silver witness for mm arm Spare silver coated blanks (for practice cleaning) BK-7 witness Could be used for silver wipe testing

30 Page 30 of 30 This report was prepared by Ian Miller, 2005 May 2 LightMachinery Inc. Director of R&D