Page 1 of 30 LIGHTMACHINERY TEST REPORT LQT 30.11-1 TITLE: HMI Michelson Interferometer Test Report Serial Number 1 - Wideband 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 7 Initial release B 2005 Apr 19 Add post-assembly, post-silvering data, remove test plan instructions C 2005 May 2 Add silver data, material data, transmission calculations,reformated D 2005 May 2 Add coating witness list E 2006 Feb 2 Changed sign of phase data in Fig. 9 to be consistent 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.
Page 2 of 30 Table of Contents 1.0 PURPOSE and SCOPE...4 2.0 DOCUMENTATION...4 3.0 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)... 10 BEAM ORTHOGONALITY (3.4)... 10 SPATIAL VARIATIONS OVER THE APERTURE (3.5)... 10 ANGULAR VARIATIONS OVER THE APERTURE (3.6)... 14 THIN FILM BEAM SPLITTER COATING... 15 TEMPERATURE DEPENDENCE (3.7)... 16 WAVEFRONT ERROR (3.8)... 17 SURFACE FLATNESS MEASUREMENTS... 18 ANTIREFLECTION COATINGS (3.9)... 20 SILVER COATINGS... 21 SURFACE QUALITY (3.10)... 23 CEMENT (3.11)... 23 ASSEMBLY DIMENSIONS AND IDENTIFICATION (3.12)... 24 MATERIAL CERTIFICATES, PROCESS CERTIFICATIONS... 28 4.0 List of Coating Witness Samples...29
Page 3 of 30 List of Figures FIGURE 1: VIEW LOOKING INTO WIDE BAND MICHELSON (0.0343 NM FSR), S/N 25 FIGURE 2: WIDE BAND MICHELSON (ON THE RIGHT) WITH ITS MATCHING NARROW BAND COUNTERPART (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)... 10 FIGURE 6: THIN FILM POLARIZER T S SPATIAL UNIFORMITY... 11 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... 15 FIGURE 11: THIN FILM POLARIZER TP VS. SAGITTAL ANGLE... 16 FIGURE 12: TRANSMITTED WAVEFRONT ERROR, 0.09Λ PEAK-TO-VALLEY... 17 FIGURE 13: INPUT/OUTPUT WAVE PLATE SURFACE FIGURE... 18 FIGURE 14: SOLID ARM WAVE PLATE EXTERNAL SURFACE FIGURE... 18 FIGURE 15: VACUUM ARM WAVE PLATE EXTERNAL SURFACE FIGURE... 19 FIGURE 16: INTERFEROGRAM OF CUBE SURFACE FACING VACUUM ARM... 19 FIGURE 17: MEASURED REFLECTIVITY OF AR 1... 20 FIGURE 18: MEASURED REFLECTIVITY OF AR 2... 21 FIGURE 19: SILVER REFLECTOR MEASUREMENT (SHOWS ALL FOUR MIRRORS FOR HMI 1 AND HMI 2 22 FIGURE 20: INPUT/OUTPUT WAVE PLATE THICKNESS MAP... 25 FIGURE 21: VACUUM ARM WAVE PLATE THICKNESS MAP... 26 FIGURE 22: SOLID ARM WAVE PLATE THICKNESS MAP... 27 FIGURE 23: MATERIAL CERTIFICATE FOR 35 MM THICK OHARA BSL7Y GLASS... 28 FIGURE 24: MATERIAL CERTIFICATE FOR 50 MM THICK OHARA BSL7Y GLASS... 28
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 wideband HMI Michelson interferometer, Serial Number 1. The Lockheed Martin part number is 65113-2H00009-102. 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 2H00025. 2.0 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-1349-0 LightMachinery Inc. Reference drawings: 1. D-OP-1349-0 HMI Fabrication process 2. D-OP-1349-22 HMI beam splitter cube 3. D-OP-1349-38 HMI polarization configuration
Page 5 of 30 Figure 1: View looking into wide band Michelson (0.0343 nm FSR), s/n 2 Figure 2: Wide band Michelson (on the right) with its matching narrow band counterpart (s/n 1)
Page 6 of 30 3.0 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 30.11. 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 73 records the variances for this instrument. Description Specification Measurement Comment Free Spectral Range 0.0344 nm ±5% 0.0343 nm -0.3%, OK (3.1) Ratio of wide band to 2.00 ±1% 1.994-0.3%, OK narrow band free spectral range (3.1) Contrast (3.2) >95% 98% 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 1.5 arc second variance plane (3.4) deviation maximum deviation Spatial variations over λ 0 variations ±0.0022 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) < ±0.0015 nm λ 0 variations < ±0.0015 nm for rays within 3 of normal incidence ±0.0014 nm OK d λ 0 /dt <0.0010 nm/ C 0.84 pm/ C OK <0.05 wave 0.09 wave variance peak-valley peak-valley R<0.2% R<0.1% OK Optical surface scratch-dig 60-40 or better Cement thickness <15 µm, visual inspection Better than 60-40 Cement thickness < 15 µm, free from bubbles inspected OK OK OK
Page 7 of 30 Free spectral range (3.1) The target value for the free spectral range of the wide band Michelson is 0.0344 nm. The free spectral range calculated from measured Michelson properties is 0.0343 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 6.350 mm 8.050 mm 43 µm 14.358 mm 6.310 mm Norland 61, 0.005 mm 4.159 mm 8.047 mm Norland 65, 0.004 mm 1.51575 (from Ohara material certificate) -0.03649/µm 0.0343 nm Ratio of wide band FSR to narrow band FSR 1.994 0.3% deviation is within 5% specification limit 0.3% deviation is within 1% specification
Page 8 of 30 Transmission and contrast (3.2) Contrast was measured with a 611.9 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 98%, 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
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 617.3 nm. The average closed transmission is 0.067% at 617.3 nm. Polarizer uniformity, closed, 3.8 mm grid, AR on one side S9 S8 S7 S6 S5 S4 S3 0.00075-0.0008 0.0007-0.00075 0.00065-0.0007 0.0006-0.00065 0.00055-0.0006 0.0005-0.00055 S2 S1 1 2 3 4 5 6 7 8 9 Figure 4: Polarizer uniformity (closed)
Page 10 of 30 Open transmission, 3.8 mm grid, AR on one side S9 S8 S7 S6 S5 S4 S3 S2 0.915-0.92 0.91-0.915 0.905-0.91 0.9-0.905 0.895-0.9 0.89-0.895 0.885-0.89 0.88-0.885 S1 1 2 3 4 5 6 7 8 9 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 1.5 seconds of perpendicular relative to their respective faces. Spatial variations over the aperture (3.5) Beamsplitter coating uniformity is shown in the plot below
Page 11 of 30 HMI Cube 04, Ts at normal incidence, 2mm grid S23 S21 S19 S17 S15 S13 S11 0.011-0.012 0.01-0.011 0.009-0.01 0.008-0.009 0.007-0.008 0.006-0.007 0.005-0.006 S9 S7 S5 S3 1 3 5 7 9 11 13 15 17 19 21 23 S1 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 ±0.0022 nm peak-valley compared to the specification of ±0.0015 nm. Standard deviation (single sided) for the λ 0 variation is 0.0008 nm. There is no significant wedge error in the assembly.
Page 12 of 30 Figure 7: Phase variation over aperture before silvering end mirrors
Page 13 of 30 Figure 8: Phase variation over aperture after silvering end mirrors
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 ±0.0014 nm, compared to the specification of ±0.0015 nm. The chart below shows the phase vs. angle data corrected for mode hops in the measurement laser and gradual drift. HMI 1 Phase vs. external angle, corrected for HeNe drift and mode hops, sign convention 40 35 corrected tangential phase corrected sagittal phase 30 Michelson phase (degrees) 25 20 15 10 5 0-5 -10-4 -3-2 -1 0 1 2 3 4 angle (external, degrees) Figure 9: Michelson phase variation vs. external angle of incidence
Page 15 of 30 Thin Film Beam Splitter Coating 0.05 0.045 0.04 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 0.035 0.03 0.025 0.02 0.015 0.01 0.005 0 600 605 610 615 620 625 630 635 640 645 Figure 10: Thin film polarizer T s, vs. angle in sagittal plane
Page 16 of 30 Tp with different sagittal angle 1 0.9 0.8 0.7 0.6 Tp 0.5 42 deg sag 0.4 43 deg sag 44 deg sag 0.3 45 deg sag 46 deg sag 0.2 47 deg sag 48 deg sag 0.1 550 570 590 610 630 650 670 690 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.
Page 17 of 30 Wavefront error (3.8) The total wavefront error measured on the Zygo interferometer is 0.09λ peak to valley, compared to the specified value of 0.05 λ. The figure below shows the transmitted wavefront error. Figure 12: Transmitted wavefront error, 0.09λ peak-to-valley
Page 18 of 30 Surface Flatness Measurements Figure 13: Input/Output wave plate surface figure Figure 14: Solid arm wave plate external surface figure
Page 19 of 30 Figure 15: Vacuum arm wave plate external surface figure Figure 16: Interferogram of cube surface facing vacuum arm
Page 20 of 30 Antireflection coatings (3.9) Vacuum facing surfaces shall be antireflection coated to R < 0.2 % at 617.3 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 beam splitter, AR 1 0.12% R at 617.3 nm vacuum arm wave plate AR coating on polarizer, input/output wave plate AR 2 <0.1% R at 617.3 nm Figure 17: Measured reflectivity of AR 1
Page 21 of 30 Figure 18: Measured reflectivity of AR 2 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.
Page 22 of 30 Figure 19: Silver reflector measurement (shows all four mirrors for HMI 1 and HMI 2
Page 23 of 30 Surface quality (3.10) All of the optical surfaces of the interferometer are better than the specified 60-40 scratch dig specification. The input/output wave plate has one visible scratch (20-40 µm wide). 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 61 227, 2004 Oct 3 BSL7Y crystal quartz Norland 61 227, 2004 Oct 3 CaF 2 BSL7Y (wave plate) Norland 65 183, 2005 July 12 BSL7Y PVA polarizer Norland 65 Cemented by Lockheed Martin BSL7Y polarizer BSL7Y cube Norland 61 230, 2005 May 14 BSL7Y input/output wave plate BSL7Y cube Norland 61 230, 2005 May 14 BSL7Y wave plate BSL7Y solid arm Norland 61 230, 2005 May 14 BSL7Y solid arm BSL7Y cube Norland 65 184, 2005 Sep 23 CaF 2 BSL7Y cube Norland 65 184, 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 1.0 1.5 Input/output wave plate 0.5 0.7 Vacuum arm 1.0 1.5 Solid arm 1.0 1.5
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 2.415 61.34 mm <64.0 mm 2.467 62.66 mm <65.0 mm Measured with Mitutoyo 3 micrometer 103-217, sn 3024721. Checked with 2.000 gauge block prior to measurements Z (height) 1.775 45.09 mm 45.0±0.1 mm Mitutoyo 2 micrometer 103-136, sn 1018456. Checked with 2.000 gauge block prior to measurements Cube dimensions Dimension Measured value Measured with X 45.08 mm Mitutoyo 2 micrometer 103- Y 45.09 mm 136, sn 3007090. Checked with 2.000 gauge block prior to Z 45.09 mm measurements Wave Plates Location Serial Number Thickness Maximum error Input/Output #10 4.0405 mm λ/550 Vacuum arm #14 8.0473 mm λ/520 Solid arm #12 8.0505 mm λ/530
Page 25 of 30 Wave Plate Thickness Measurements Figure 20: Input/Output wave plate thickness map
Page 26 of 30 Figure 21: Vacuum arm wave plate thickness map
Page 27 of 30 Figure 22: Solid arm wave plate thickness map
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 23: Material certificate for 35 mm thick Ohara BSL7Y glass Figure 24: Material certificate for 50 mm thick Ohara BSL7Y glass The crystal quartz used in this instrument was supplied by Sawyer Research. The material code is SP00356-000. The calcium fluoride spacers were fabricated from
Page 29 of 30 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 702415. 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-1835. Silver coatings were applied to our specification CT-1852. The polarizing beam splitter coating was applied by Iridian Spectral technologies; their run number #ds-bv-000009b000 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 14.30 mm arm HMI 1 vacuum arm BSL7Y silver witness 12.16 mm arm HMI 2 solid arm BSL7Y silver witness for 20.66 mm arm HMI 2 vacuum arm BSL7Y silver witness for 16.32 mm arm Spare silver coated blanks (for practice cleaning) BK-7 witness 12.16 14.30 16.32 20.66. Could be used for silver wipe testing
Page 30 of 30 This report was prepared by Ian Miller, 2005 May 2 LightMachinery Inc. Director of R&D