Improvements in the accuracy and the repeatability of long trace profiler measurements

Abstract

Modifications of the long trace profiler at the Advanced Photon Source at Argonne National Laboratory have significantly improved its accuracy and repeatability for measuring the figure of large flat and long-radius mirrors. Use of a Dove prism in the reference beam path corrects phasing problems between mechanical errors and thermally induced system errors. A single reference correction now completely removes both of these error signals from the measured surface profile. The addition of a precision air conditioner keeps the temperature in the metrology enclosure constant to within +/-0.1 degrees C over a 24-h period and has significantly improved the stability and the repeatability of the measurements. Long-radius surface curvatures can now be measured absolutely with a high degree of confidence. These improved capabilities are illustrated with a series of measurements of a 500-mm-long mirror with a 5-km radius of curvature. The standard deviation in the average of ten slope profile scans is 0.3 microrad, and the corresponding standard deviation in the height error is 4.6 nm.

Nano-Accuracy Surface Figure Metrology of Precision Optics

“…Having the reference beam centered in the lens aperture minimizes the introduction of phase shifts by glass inhomogeneities that translate into beam spot location variations with lateral movement of the beam across the aperture during a long scan. Bresloff added a Dove prism into the reference beam to change the phase of the laser pointing direction drift to be the same as the mechanical pitch angle error, allowing for correction of both error signals simultaneously by addition of the two signals (Takacs & Bresloff, 1986;Takacs et al, 1999). A sketch of the LTP-II optical head is shown in Fig.…”

Proposal for a universal test mirror for characterization of slope measuring instruments

“…Since the development of the first LTP based on a pencil-beam interferometer, [6][7][8] investigations to determine the LTP limiting factors and to find the ways to overcome them have been carried out at practically all facilities [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] It should be mentioned that most sources of systematic errors and random noise are common for the LTP and for the principally different slope profilers NOM 9 and ESAD (Extended Shear Angle Difference Shearing Deflectometer 28 ) based on a high precision autocollimator and developed at BESSY and the PTB, respectively. Compared to the classical LTP-II the progress of 2 nd generation slope measuring instruments like the NOM and the ESAD is based on an advanced design of the instruments and high stability of their environmental conditions.…”

Design of a machine for the universal non-contact measurement of large free-form optics with 30 nm uncertainty

“…The air bearings will be pre-loaded with opposite piston mounted air-bearings through the preload frames (9). The Z-stage further contains a ceramic tube (10), the two sides of which will be used to constrain the R and ψ motion relative to the R-stage via two ∅150 mm air bearings (11). A motor and weight compensation are added.…”