Metrology Equipment

• CMM is used for measuring parts, optics, and for alignment of optical assemblies

• Measuring Volume (700w x 1000d x 660h mm)

• Accuracy, maximum permissible error (MPE) for measurement of length L: MPE = 1.5 + L/333 microns

  • e.g., for L = 1000 mm, MPE = 4.5 microns

• Measuring range: 3-meter spherical volume

• Point repeatability: 30 microns

• Volumetric accuracy: 44 microns

• Usage: Measure larger optical/mechanical systems and parts which do not fit in CMM or must be measured in-situ

• Used for measuring very large parts and optical alignments of complex systems (e.g. GMT Wide Field Phase Testbed (WFPT), GMT G-CLEF spectrograph)

• Accuracy = +/- (15 um + 6um x L m)

  • where L = measurement distance

  • e.g. for L = 2 m, Accuracy = 15 + 12 = 27 um

• CE has several alignment telescopes used for optical alignments, e.g. Brunson, K & E

Used for measurement of angles, typically of use in optical alignments e.g. AIA, IRIS, Hi-C

• Used to dynamically measure mirror LOS angles, e.g. piston tip/til assembly, steering mirror control accuracy, pickoff mirror tip/tilt accuracy on (e.g.) WFTP, AGWS and G-CLEF projects

• Sub arcsecond accuracy

• General purpose with 6-inch aperture, but set up on 5 axis stage for telescope alignments

• Measure surface errors on flats, convex and concave spheres, aspheres

• Measure transmitted wavefront errors on refractive elements and systems

• Six-inch apertures using transmission flats and spheres

• Measure surface errors on flats, convex and concave spheres, aspheres

• Measure transmitted wavefront errors on refractive elements and systems

• Accuracy governed by transmission elements; λ/20 for flats, λ/10 to λ/40 for spheres

• For optical system alignments using diverger lenses

• Measure system wavefront errors in double pass

• Measure surface errors of concave parts

• Accuracy gated by diverger lens, typically λ/8 PV