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MIC- 1 Interferograms Serial #915. Modern Optical Metrology Techniques used in James Webb Space Telescope Segment Optics and Space Instruments. Square flat mirror. Laser radar. Concave Mirror. Laser beam. 2. Less Tilt with better alignment. 1. High Tilt. Spherical mirror.
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Modern Optical Metrology Techniques used in James Webb Space Telescope
Segment Optics and Space Instruments
Square flat mirror
2. Less Tilt with better alignment
1. High Tilt
Circular flat mirror
Agossa Segla1, Edwin Olaya1, Viviana Vladutescu1Phillip Coulter2, Theo Hadjimichael2, Raymond Ohl2
1 Department of Electrical and Telecommunications Engineering, New York City College of Technology
2Instrument Systems and Technology, Optics Division, NASA Goddard Space Flight Center
Fig. 5. Tip-tilting the spherical mirror to get a higher return power
Theoretical background cont’d
Procedure for Mirror scan
Deep space studies have been of high interest for wide range of space investigations. James Webb Space Telescope (JWST), the follower of Hubble, will be launched in 2018 with the scope of exploring the universe and improving our understanding of processes such as the assembly and evolution of galaxies, star birth, first light, reionization, and the formation of planets orbiting other stars as well as objects in our solar system. The JWST’s telescope collects light from distant stars and galaxies, has sensors that convert that light into digital images and spectra. The presented work involves non-contact measurements of mechanical and optical system components on JWST. In general, the calibration of the uncalibrated laser unequal path interferometer (LUPI) was performed successfully and also the LR measured the surface of the gold concave mirror with a high accuracy.
Surface error calculation
Circular flat mirror errors measured
with interferometer SN 913
with interferometer SN 915
Methods and instruments
Fig. 4. Set up for LR measurement
T = time, c=speed of light
Fig. 6. Interferogram comparison from Interferometer s S/N 913 and S/N915 (qualitative comparison presented here)
Since we are using the ratio of Δ/S absolute values are not necessary
Two-beam interference fringes
Fig. 3. 1 MIC-1 Interferometer (LUPI) with alignment aperture screen (5)
Fig. 7. 1 Scanned mirror,
2 SA instruments scanning the mirror
R = radius of curvature of the mirror
D = diameter of the mirror
F = focal length of the mirror
F# = f number
The results showed in the first project showed a surface error height uncertainty of 47.46 nm which is the accuracy of our calibration of the LUPI. In the second project, F# of 2.051 was deducted from the radius obtained from SA after fitting the measured gold spherical mirror with the SA's CAD model. This measurement gave an acceptable error of 0.5% when compared to the actual F# of 2 of the mirror. The calibration of the LUPI was performed successfully and the LR measured the surface of the gold concave mirror with a high accuracy.
1. Set up the optics and place the Tooling Balls (TB) in the proximity of the mirror (the actual tooling balls were 0.5 inch in size and were placed on the stand of the mirror so we could change the position of the mirror instead of changing the position of the LR points to a shape (spherical)
2. Turn on the LR and Add instrument Metris Laser RADAR into SA
3. In SA connect to the LR
4. Measure TB positions
5. Scan spherical gold mirror to determine size and edges
6. Change LR position and repeat Step 5
7. Fit the scanned points from the different positions into the same XYZ coordinate system
8. Fit the mirror scanned
References and Acknowledgments
Fig. 1. Schematic of MIC-1 Interferometer
Fig. 2. Destructive and constructive interference requirements