Working Principle

All PICOSCALE products are based on a Michelson interferometer, a precise method to measure displacements and vibrations. The Michelson interferometer consists of a wavelength-stabilized laser, a beam splitter, a target and a reference mirror. At the beam splitter, the light from the laser is divided into two arms. One arm is directed to the target surface while the other is directed to the reference mirror. After the light of both arms is reflected by the target surface and reference mirror, respectively, it travels back to the beam splitter. Here, both arms recombine and interference takes place. The interference signal contains information on the displacement of the target surface with respect to the reference mirror.

Schematic setup of a sensor head

 

Specifications

 
PICOSCALE Interferometer
Resolution [pm] 1
Repeatability [nm] 1

Accuracy [nm]

Accuracy (length proportional)

3

10

RMS Noise [pm] 70*
Amplitude Spectral Density [pm] 1 @ 1000 Hz
Long Term Stability [nm} 1*
Maximum Target Velocity [m/s] 2
Target Reflectivity 4% - 100%
Maximum Working Distance [mm] 1000
Absolute Position Estimation 1% of working distance

*Working distance 20 mm, ambient conditions, measurement bandwidth 1.2 kHz