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Displacement Measurements

Key features

Position stability50 pm (depending on streaming frequency, read more)
Working distance0-1000 mm (depending on sensor head, read more)
Maximum target velocity1 m/s ( read more)
Possible targetsMirror, Retro-reflector, target reflectivity >4%
Measurement conditionsAmbient, high vacuum, ultra-high vacuum, cryogenic
Environmental compensationPossible with Environmental Module

Position stability

A PICOSCALE interferometer head and a target mirror were mounted into a box to reduce air fluctuations. The setup was placed in an SEM chamber at ambient pressure. The working distance between interferometer head and mirror was 20 mm. With this setup, position data was recorded from the interferometer for 20 seconds at 156 kHz. The time signal was recorded and plotted in the histogram to show the distribution of the position data over time.

Except of subtracting the average value to center the distribution at zero, no post-processing of the data was carried out. From the histogram it can be seen that the distribution is approximately Gaussian-shaped, and the standard deviation of the position data can be evaluated. The standard deviation increases slightly with streaming frequency because of the bandwidth.

Long-term position stability

Another measurement was done to show the long-term position stability of the PICOSCALE. Therefor the controller was placed in standard laboratory environment (± 0.5 °C), while sensor and target were temperature stabilized (± 0.02 °C).

The whole experiment was operated in air and environmental fluctuations (mainly air pressure) were recorded with the PICOSCALE environmental module. Afterwards the data were corrected for the fluctuations of the environmental conditions.

The following graphs show that the PicoScale is able to track displacements of a target with sub-nanometer resolution even on very long time scales.

True Differential Measurements

The PICOSCALE is based on a Michelson interferometer which allows to also guide the reference beam out of the sensor head and thus to perform true differential measurements. This way the motion of a device under test with respect to the displacement/drift of a second target can be perfomed with a single sensor head.

The PICOSCALE is the only low-cost commercial displacement sensors allowing for true differential interferometric measurements!

Application Notes

PICOSCALE resolution and stability Download AppNote

High speed displacement measurements Download AppNote