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 over
12 hrs. Short -term data are recorded at
10 Hz over 10 seconds.
Long-term picometer stability
The intrinsic position signal stability of the FPS sensor is unsur-
passed - making it challenging to demonstrate the performance of
FPS sensors with standard tools and equipment. The measurements
shown above were therefore recorded on an evacuated reference cav-
ity with a relative length stability Δl/l well below 10 -8 . This stability
was achieved by temperature stabilizing the titanium cavity within
few mK at liquid helium temperature (-269 °C).
Due to the low coefficient of thermal expansion at said temperature,
the titanium cavity provides a reference in length approximately 10
times more stable than a corresponding ultra-low-expansion glass
(ULE) cavity at ambient conditions. The plot shows position sensing
data recorded on a 20 mm long cavity during a 12 hour period of time.
The bandwidth of the measurement was 100 Hz.
(attocube applications labs, 2012)