1. Our Operating Funding Partners www.lightsource.ca Recent Design Improvements to the Canadian Light Source (CLS) Optical Metrology Facility Long Trace Profilometer Brian Yates *, Alan Duffy *, Shawn Carriere * (* CLS) A design upgrade was recently initiated for the long trace profilometer (LTP) at the Canadian Light Source that allows radius of curvature measurements, on large mirror benders, as a function of bending force prior to beamline installation. The LTP vertical clearance can now handle mirror benders up to approximately 500 mm in height. A decoupled external enclosure reduces air convection current effects, and vertical adjustment of the main beam can be safely performed by one person, with no realignment of the LTP reference light beam. Design criteria and recent stability scan results will be discussed. Motivation The need arose from two CLS hard x-ray beamlines that use relatively large mirror bender mechanisms in their designs. There was a requirement prior to installation to measure these mirror bender systems to determine the radius of curvature as a function of bending force, and to verify that the overall slope error (mirror plus bender) met specifications. A design that provides adequate vertical clearance between the LTP optical head and the mirror bender system was required. Fig. 1 shows the LTP prior to the system upgrade. The need arose from two CLS hard x-ray beamlines that use relatively large mirror bender mechanisms in their designs. There was a requirement prior to installation to measure these mirror bender systems to determine the radius of curvature as a function of bending force, and to verify that the overall slope error (mirror plus bender) met specifications. A design that provides adequate vertical clearance between the LTP optical head and the mirror bender system was required. Fig. 1 shows the LTP prior to the system upgrade. Discussion Mirror bender mechanisms up to 500 mm in height should be measurable. Mirror bender mechanisms up to 500 mm in height should be measurable. More rigid support of the LTP main beam to achieve sub-microradian stability. More rigid support of the LTP main beam to achieve sub-microradian stability. Eliminate realignment issues of the reference light beam with a change in LTP main beam height.Eliminate realignment issues of the reference light beam with a change in LTP main beam height. An external enclosure that is decoupled from the LTP and vibration isolation table to reduce air convection currents. An external enclosure that is decoupled from the LTP and vibration isolation table to reduce air convection currents. All operations of the LTP should be directly viewable and accessible from the front access doors. All operations of the LTP should be directly viewable and accessible from the front access doors. Vertical adjustment of the LTP main beam can be safely performed by one person. Vertical adjustment of the LTP main beam can be safely performed by one person. A series of stability tests were carried out as a function of scan duration time to estimate our “noise floor”, keeping the LTP position fixed. For this test essentially “identical” super-polished silicon mirrors from General Optics (Catalogue Number GO-S100-1) were used for both the reference beam and the sample. Fig. 5 shows the LTP stability test with scan duration times ranging from 30 to 600 seconds. It is interesting to note that although the average sample beam slope error contribution is 83 nrad RMS, the “bottleneck” appears to lie more with the reference beam which has a much higher average slope error contribution of 270 nrad RMS. Typically when measuring a mirror the two signals are either added or subtracted from one another (phasing depends on the setup) to correct for the fluctuations in the straightness of the LTP main beam. As a result an actual mirror measurement is currently limited to this noise floor of ~300 nrad. A series of test fans was set up to mix the air through which the reference beam passes, to break up convection cells and avoid air stratification, but the stability tests were either unchanged or slightly worse than that shown in Fig. 5. In order to further reduce the LTP noise floor we are looking into improving our room temperature stability (from ±0.1 to ±0.01 degrees centigrade), and replacing the main LTP aluminum beam with a ceramic beam from Coorstek, Inc., with substantially better flatness of ~5 μrad RMS, higher stiffness, and lower coefficient of thermal expansion. The design used extruded aluminum beams from MK Profile [1] to build a rigid support system for the main LTP beam and enclosure. The surrounding enclosure is isolated from the vibration isolation table and LTP main beam by a small clearance gap. The enclosure has three floor-mounted support legs and a fourth support at the back wall. Transparent 0.25” polycarbonate sheets enclose the top and side panels of the external isolated enclosure, using rubber grommets for additional vibration isolation. Fig. 2 shows the LTP and enclosure with a mirror bender under test, and Fig. 3 shows a back view of the LTP. The two aluminum towers supporting the LTP main beam were precision machined from solid aluminum 4”x4” bar (Type 6061-T6), with thirty five precisely drilled holes in each, allowing LTP beam height adjustments over a total range of 510 mm, to within 15 mm. An expanding pin is used to align both sides of the main beam to equal height, to better than 1 mrad levelness. Once level the two bolts beside each expanding pin are tightened to lock the LTP main beam down, and the expanding pins removed. The reference mirror is mounted fixed relative to the main beam, eliminating reference mirror readjustments. Fig. 4 shows an expanding pin locked in one of the hole. A removable worm gear hand winch (McMaster-Carr Part. No. 3205T16, load capacity of 2000 lbs.) was used to lift the main LTP beam using 3/16” stainless steel braided cables. The hand winch employs a 41:1 gear ratio and is of a “no back drive” design so a single person can raise or lower the LTP main beam. Two cables are employed on the worm gear – one to raise the right portion of the LTP beam, the other to simultaneously raise the left portion through a longer cable and adjustment turnbuckle. The turnbuckle allows the tension of the two cables to be matched. Typically the entire worm gear mechanism and cables are removed once the desired height has been achieved. [1] MK is the copyright for Maschinebau Kitz. Design Criteria Stability Tests Figure 3: Back view of the upgraded LTP showing the rigid support structure for the main beam (before external decoupled enclosure assembly). The worm gear hand winch (center portion) and wire/pulley system (middle-top portion) raises or lowers the main LTP beam to the desired height. Figure 2: Front view of the upgraded CLS Long Trace Profilometer (front doors open), showing adjustable height adjustment and external decoupled enclosure. Under measurement is a 1.1 m length vertically collimating mirror bender system mounted on an adjustable tip/tilt stage. Figure 4: Front view of the left tower support structure showing the wire/pulley system and anchor shackle/eyebolt that can be used to raise or lower the main LTP beam. Also visible are the precision drilled holes in the tower (15 mm spacing over a range of 510 mm) to which the height can be adjusted, and the lever/expanding pin that is used to align and level both sides to better than 1 mrad, before lock-down. Figure 5: LTP stability versus scan duration time. The sample and reference beam data have been shown separately for comparison purposes, and have had a best fit constant removed. The ±1s error bars shown were determined from seven measurements. Acknowledgements The CLS is supported by NSERC, NRC, CIHR, and the University of Saskatchewan. The CLS is supported by NSERC, NRC, CIHR, and the University of Saskatchewan. Figure 1: Front view of the CLS Long Trace Profilometer prior to the system upgrade shown with a small mirror under test. Motivation