attoPUBLICATIONS attoCATALOG-2015/16 | Page 202

FPS Sensor Systems PAGE 200 Selected Measurements unsurpassed signal stability Measured Long-Term Signal Stability working distance [mm] 2σ [nm] 20 0.286 50 0.530 100 1.035 Measured Short-Term Signal Stability working distance [mm] 2σ [nm] 30 0.039 Long-term FPS signal stability as demonstrated on a  20 mm long Titanium vacuum reference cavity. The cavity is cooled to liquid helium temperature (-269 °C) in order to minimize thermal expansion/contraction. 68% of all position measurement data points lie within 286 pm, as measured at a 100 Hz bandwidth