Page 1 of 34 LIGHTMACHINERY TEST REPORT LQT 30.11-3 TITLE: HMI Michelson Interferometer Test Report Serial Number 3 wide band 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 NR 2006 Jan 31 Initial creation A 2006 Feb 3 First release Note: All documentation is subject to change, and therefore you must check the company data base for the current Document Revision.
Page 2 of 34 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)... 16 THIN FILM BEAM SPLITTER COATING... 17 TEMPERATURE DEPENDENCE (3.7)... 19 WAVEFRONT ERROR (3.8)... 20 SURFACE FLATNESS MEASUREMENTS... 21 ANTIREFLECTION COATINGS (3.9)... 23 SILVER COATINGS... 26 SURFACE QUALITY (3.10)... 27 CEMENT (3.11)... 27 ASSEMBLY DIMENSIONS AND IDENTIFICATION (3.12)... 28 MATERIAL CERTIFICATES, PROCESS CERTIFICATIONS... 32 4.0 List of Coating Witness Samples...33
List of Figures LQT 30.11-3, Rev A Page 3 of 34 FIGURE 1: NARROW BAND MICHELSON (S/N 2), COMPLETE. KAPTON TAPE IS WRAPPED ON THE VACUUM ARM TO PROTECT THE VACUUM GLASS INTERFACES... 5 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: PVA POLARIZER OPEN TRANSMISSION, UNCORRECTED FOR FRESNEL LOSSES 9 FIGURE 5: PVA POLARIZER CLOSED TRANSMISSION... 10 FIGURE 6: THIN FILM POLARIZER T S SPATIAL UNIFORMITY... 11 FIGURE 7: THIN FILM POLARIZER T P SPATIAL UNIFORMITY... 12 FIGURE 8: PHASE VARIATION OVER APERTURE AFTER SILVERING END MIRRORS13 FIGURE 9: PHASE VARIATION OVER APERTURE AFTER SILVERING END MIRRORS WITH TILT REMOVED 14 FIGURE 10: PHASE VARIATION OVER APERTURE BEFORE SILVERING END MIRRORS15 FIGURE 11: MEASURED MICHELSON PHASE VARIATION VS. EXTERNAL ANGLE OF INCIDENCE 16 FIGURE 12: THIN FILM POLARIZER T S, VS. ANGLE IN SAGITTAL PLANE... 17 FIGURE 13: THIN FILM POLARIZER TP VS. SAGITTAL ANGLE... 18 FIGURE 14: PHASE CONTRIBUTION FROM POLARIZING BEAM SPLITTER COATING. 19 FIGURE 15: TRANSMITTED WAVEFRONT ERROR, 0.07Λ PEAK-TO-VALLEY... 20 FIGURE 16: INPUT/OUTPUT WAVE PLATE SURFACE FLATNESS... 21 FIGURE 17: INPUT/OUTPUT POLARIZER SURFACE FLATNESS... 21 FIGURE 18: VACUUM ARM WAVE PLATE EXTERNAL SURFACE FIGURE... 22 FIGURE 19: VACUUM ARM WAVE PLATE INTERNAL SURFACE FIGURE (AR COATED) HMI 3 22 FIGURE 20: INTERFEROGRAM OF CUBE SURFACE FACING THE VACUUM ARM... 23 FIGURE 21: MEASURED REFLECTIVITY OF AR E, APPLIED TO VACUUM ARM WAVE PLATE AND FACING CUBE FACE... 24 FIGURE 22: MEASURED REFLECTIVITY OF AR F, APPLIED TO INPUT/OUTPUT WAVE PLATE AND POLARIZER... 25 FIGURE 23: SILVER REFLECTOR COATING RUNS G3 BLUE LINE, APPLIED TO THE SOLID ARM, G4 RED LINE, APPLIED TO THE VACUUM ARM... 26 FIGURE 24: INPUT/OUTPUT WAVE PLATE THICKNESS MAP... 29 FIGURE 25: VACUUM ARM WAVE PLATE THICKNESS MAP... 30 FIGURE 26: SOLID ARM WAVE PLATE THICKNESS MAP... 31 FIGURE 27: MATERIAL CERTIFICATE FOR 35 MM THICK OHARA BSL7Y GLASS... 32 FIGURE 28: MATERIAL CERTIFICATE FOR 50 MM THICK OHARA BSL7Y GLASS... 32
Page 4 of 34 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 3. 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 34 Figure 1: Narrow band Michelson (s/n 2), 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)
Page 6 of 34 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 74 records the variances for this instrument. Description Specification Measurement Comment Free Spectral Range 0.0344 nm ±5% 0.03431 nm OK (3.1) Ratio of wide band to 2.00 ±1% 1.995 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 1.4 arc second variance plane (3.4) deviation maximum deviation Spatial variations over λ 0 variations ±0.0028 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 ±0.0010 nm OK d λ 0 /dt <0.0010 nm/ C 0.84 pm/ C OK <0.05 wave 0.07 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 34 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.03431 nm. The table below shows the measured component thicknesses and the calculated free spectral range. 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 6.3497 mm 8.052 mm 44 µm 14.365 mm mm Norland 65, 0.005 mm 4.1585 mm 8.052 mm Norland 65, 0.004 mm 1.51575 (from Ohara material certificate) -0.03649/µm 0.03431 nm Ratio of wide band FSR to narrow band FSR 1.995 <0.3% deviation is within 5% specification limit <0.3% deviation is within 1% specification limit
Page 8 of 34 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
Page 9 of 34 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 >97% 95% Polarizer transmission >90% Transmission (3.2) >80% >82% OK Contrast 98% average 95% OK PVA Polarizer Uniformity The input/output polarizer uniformity was measured on a 1.5 mm pitch. The data here were measured with the polarizer uncoated. The minimum open transmission is 83%. When allowance is made for Fresnel losses, the minimum transmission is 90%. The average transmission is 92% and the maximum transmission is 93%. The maximum transmission of the closed polarizer is approximately 0.2%. PVA Polarizer, open, uncoated S27 S25 S23 S21 S19 S17 S15 S13 S11 S9 0.87-0.88 0.86-0.87 0.85-0.86 0.84-0.85 0.83-0.84 0.82-0.83 S7 S5 S3 1 3 5 7 9 11 13 15 17 19 21 23 25 27S1 Figure 4: PVA polarizer open transmission, uncorrected for Fresnel losses
Page 10 of 34 PVA polarizer, closed S27 S25 S23 S21 S19 S17 S15 S13 S11 S9 0.0019-0.002 0.0018-0.0019 0.0017-0.0018 0.0016-0.0017 0.0015-0.0016 S7 S5 S3 1 3 5 7 9 11 13 15 17 19 21 23 25 27S1 Figure 5: PVA polarizer closed transmission 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 1.4 seconds of perpendicular relative to their respective faces. Spatial variations over the aperture (3.5) Beamsplitter coating uniformity is shown in Figure 6 and Figure 7 below. This data was collected on a 1.5 mm x 1.5 mm grid.
Page 11 of 34 Cube polarizer Ts at normal incidence S25 S23 S21 S19 S17 S15 S13 S11 S9 0.004-0.0045 0.0035-0.004 0.003-0.0035 0.0025-0.003 0.002-0.0025 S7 S5 S3 1 4 7 10 13 16 19 22 25 S1 Figure 6: Thin film polarizer T s spatial uniformity
Page 12 of 34 Cube polarizer Tp at normal incidence S27 S25 S23 S21 S19 S17 S15 S13 S11 S9 S7 S5 0.996-1 0.992-0.996 0.988-0.992 0.984-0.988 0.98-0.984 0.976-0.98 0.972-0.976 0.968-0.972 0.964-0.968 0.96-0.964 S3 1 4 7 10 13 16 19 22 25 S1 Figure 7: Thin film polarizer T p 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 ±0.0028 nm peak-valley compared to the specification of ±0.0015 nm. Standard deviation (single sided) for the λ 0 variation is 0.0012 nm. Approximately 50% of the total phase error is due to wedge in the assembly. Hand written numbers for wedge and power show the contributions of these particular errors to the measured error. This instrument is sensitive to temperature gradients and fluctuations. Temperature changes in the test room have a strong influence on the performance of the instrument, and the total phase uniformity should be rechecked once the Michelson is mounted in a temperature controlled oven. Prior to silvering the total phase variation was approximately ±0.0017 nm. The phase variation of the other three Michelsons was not significantly affected by the silvering process, and as a consequence, the change in phase variation after silvering is thought to be due to the change in ambient test conditions. It is not known whether the before or after silvering environment is closer to ideal. All previous phase testing was performed with the clean bench in the test room. The large fan on the clean bench had several possible effects on the test room. First it increased the room temperature by 1-2 C. This change should not be significant. The second effect of the clean bench is to
Page 13 of 34 mix the air in the room more thoroughly than with the normal building ventilation. Finally, the clean bench raises the temperature of the air, and directs this stream of warm air toward the Michelson test set up. Figure 8: Phase variation over aperture after silvering end mirrors
Page 14 of 34 Figure 9: Phase variation over aperture after silvering end mirrors with tilt removed
Page 15 of 34 Figure 10: Phase variation over aperture before silvering end mirrors
Page 16 of 34 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 ±0.0010 nm, compared to the specification of ±0.0015 nm. The chart below shows the phase vs. angle data measured over the central 20 mm of the instrument. The tangential and sagittal phase models are based on a solid arm excess length of 16 µm, and coating phase calculated by Iridian based on the actual beam splitter coating run. Michelson phase at 611.9 nm (degrees) HMI 3 Field Widening Measurement 25 20 15 10 5 0-5 -10 Sagittal measurement Tangential measurement Tan. phase model Sag. phase model -5-3 -1 1 3 5 External Angle of Incidence (degrees) Figure 11: Measured Michelson phase variation vs. external angle of incidence
Page 17 of 34 Thin Film Beam Splitter Coating Ts with different sagittal angle for wavelength 600-650nm 0. 25 0. 2 0. 15 AOI 42 deg AOI 43 deg AOI 44 deg AOI 45 deg AOI 46 deg AOI 47 deg AOI 48 deg Ts 0. 1 0. 05 0 600 610 620 630 640 650 Wavelength/nm Figure 12: Thin film polarizer T s, vs. angle in sagittal plane
Page 18 of 34 Tp with different sagittal angle for wavelength 550-700nm 1 0.9 0.8 0.7 Tp 0.6 0.5 0.4 0.3 0.2 0.1 AOI 42 deg AOI 43 deg AOI 44 deg AOI 45 deg AOI 46 deg AOI 47 deg AOI 48 deg 0 550 570 590 610 630 650 670 690 wavelength/nm Figure 13: Thin film polarizer Tp vs. sagittal angle
Page 19 of 34 Beam splitter phase contribution 15 Net phase from beam splitter (degrees) 10 5 0-5 -10-15 -20-25 -30 42.0 43.0 44.0 45.0 46.0 47.0 48.0 Beam splitter angle of incidence (degrees) Figure 14: Phase contribution from polarizing beam splitter coating. The beam splitter phase is calculated from monitored thin film deposition. Net phase = φ Rs1 +φ Tp2 -(φ Tp1 +φ Rs2 ). Although the coating is designed to be symmetric from front to back, during the deposition process small corrections were made to optimize the coating performance resulting in slight asymmetry of the deposited coating. 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 20 of 34 Wavefront error (3.8) The total wavefront error measured on the Zygo interferometer is 0.07λ peak to valley, compared to the specified value of 0.05 λ. The figure below shows the transmitted wavefront error. Figure 15: Transmitted wavefront error, 0.07λ peak-to-valley
Page 21 of 34 Surface Flatness Measurements Figure 16: Input/output wave plate surface flatness Figure 17: Input/output polarizer surface flatness
Page 22 of 34 Figure 18: Vacuum arm wave plate external surface figure Figure 19: Vacuum arm wave plate internal surface figure (AR coated)
Page 23 of 34 Figure 20: Interferogram of cube surface facing the vacuum arm Antireflection coatings (3.9) All anti-reflection coatings were measured to have a reflectivity less than 0.1% at 617.3 nm. The nominal aperture of the coatings on the input/output wave plate and polarizer is 42 mm, and the nominal aperture of the coatings on the cube and vacuum arm wave plate is 34 mm to allow clearance for the vacuum arm spacer. Coating location Coating ID Notes AR on vacuum arm AR E 0.1% R at 617.3 nm wave plate AR on input/output AR F 0.05% R at 617.3 nm wave plate AR on beam splitter AR E 0.1% R at 617.3 nm cube (facing vacuum arm) AR on polarizer AR F 0.05% R at 617.3 nm
Page 24 of 34 Figure 21: Measured reflectivity of AR E, applied to vacuum arm wave plate and facing cube face
Page 25 of 34 Figure 22: Measured reflectivity of AR F, applied to input/output wave plate and polarizer
Page 26 of 34 Silver Coatings The measured reflectivity of the silver coatings on the solid and vacuum arms is greater than 97%. The figure below shows the reflectivity of the coatings applied to HMI 3. Figure 23: Silver reflector coating runs G3 blue line, applied to the solid arm, G4 red line, applied to the vacuum arm
Page 27 of 34 Surface quality (3.10) All of the optical surfaces of the interferometer are better than the specified 60-40 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 61 233, 2005 Dec 4 BSL7Y crystal quartz Norland 65 184, 2005 Sep 23 CaF 2 BSL7Y (wave plate) Norland 65 185, 2005 Dec 6 BSL7Y PVA polarizer Norland 65 Cemented by Lockheed Martin BSL7Y polarizer BSL7Y cube Norland 65 185, 2005 Dec 6 BSL7Y input/output wave plate BSL7Y cube Norland 65 185, 2005 Dec 6 BSL7Y wave plate BSL7Y solid arm Norland 65 188, 2006 Sep 28 BSL7Y solid arm BSL7Y cube Norland 65 188 2006 Sep 28 CaF 2 BSL7Y cube Norland 65 185, 2005 Dec 6 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 1.4 Input/output wave plate 0.5 0.7 Vacuum arm 0.5 0.7 Solid arm 0.5 0.7
Page 28 of 34 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 2.416 61.37 mm <64.0 mm 2.461 62.50 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 45.08 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 45.09 mm Mitutoyo 2 micrometer 103- Y 45.06 mm 136, sn 3007090. Checked with 2.000 gauge block prior to Z 45.08 mm measurements Wave Plates Location Serial Number Thickness Maximum error Input/Output #25 4.059 mm -λ/1400 λ/1900 Vacuum arm #27 8.052 mm -λ/680 λ/2800 Solid arm #28 8.052 mm -λ/420 -λ/790 Note that the wave plate test set up had a small amount of systematic birefringence which was compensated by averaging the results of two measurements with the wave plate rotated 90 between measurements. The thickness plots that follow show the uniformity, but have not been corrected for this systematic error. The table above shows the corrected measurements. The maximum errors are the greatest deviations from the nominal three quarter wave retardation at 617.3nm on both the high side and the low side.
Page 29 of 34 Wave Plate Thickness Measurements Figure 24: Input/Output wave plate thickness map
Page 30 of 34 Figure 25: Vacuum arm wave plate thickness map
Page 31 of 34 Figure 26: Solid arm wave plate thickness map
Page 32 of 34 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 27: Material certificate for 35 mm thick Ohara BSL7Y glass Figure 28: Material certificate for 50 mm thick Ohara BSL7Y glass
Page 33 of 34 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 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 702416. 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 bxft615b 4.0 List of Coating Witness Samples The following table lists coating witness for all of the coating runs used in fabricating HMI 3. Coating Witness Identification Polarizing beam splitter #ds-bv-000009b000 bxft615b Iridian HMI B/S AR E Nov 10/05 AR on B/S + WP #27 AR F BSL7Y Lockheed AR witness WP #25 Polarizer Nov 14/05 HMI 4 solid arm BSL7Y silver witness for 14.30 mm arm HMI 4 vacuum arm BSL7Y silver witness 12.16 mm arm
Page 34 of 34 This report was prepared by Ian Miller, 2006 February 3 LightMachinery Inc. Director of R&D