<title>Self-referencing, motion-insensitive approach for absolute aspheric profiling of large optics to the nanometer level and beyond</title>

The Reconnection And Microscale (RAM) Solar-Terrestrial Probe

“…has initiated a third--scale mirror fabrication effort designed primarily to develop the necessary metrology verify the figure for this long a focal length, as well as the mount performance. The metrology system, developed by Bauer Associates, has been reported on elsewhere 34,35 , and is capable of meeting the RAM requirements. The primary and secondary mirrors are also measured interferometrically using a phase-shifting point-diffraction interferometer.…”

“…Ultra-high precision optics and metrology (TRL 6): Comparable size/quality are currently fabricated for X-ray lithography, though slightly smaller than the primary optic of the HRI (0.5m vs. 0.65m). Specialized metrology 34,35 has been developed under a technology development program to measure the surface figure and radius of curvature of the RAM HRI primary optic. These technologies have already shown 0.1nm sensitivities and 2nm repeatability without any effort at thermal control of the metrology system , 35. 5.…”

System of four distance sensors for high-accuracy measurement of topography

“…More recently, a similar system was again proposed [16] together with an alternative experimental realization. Another system was suggested [17,18] using four or more sensors located on a rotating ring scanning the artifact.…”

“…Basically, such systems can be classified according to the measurand: most common are systems with the distance [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], the slope [21][22][23][24][25][26][27][28] or the curvature [29][30][31] as the measurand.…”

“…The evaluation procedures used in[15,18] are based on the construction of second order differences the use of which directly eliminates the influences of the pitch and slope scan errors. The results for the three-sensor system shown in the Figs.…”