High precision contactless measurement of displacements

For the high precision measurement of displacements, SmarAct provides the PICOSCALE interferometer.

  • 3 parallel laser interferometers in one instrument for 3D measurements
  • Measurement bandwidth up to 2.5 MHz (10 MHz sample rate) with a resolution down to 1 pm1
  • Measurements possible on most materials (plastic, glass, metal and even water)
  • Wide range of sensor heads available for different applications and environments (including vacuum and cryogenics)
  • Extendable to a complete laboratory measurement and control instrument with optional modules
  • Proven performance with 100s of satisfied customers

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1 When analysing periodic displacements in the frequency domain

Product Presentation

Application Examples

For an overview of all application notes click here.

Straightness measurements of translation stages

Straightness measurements of translation stages are one of the typical applications for the PICOSCALE Interferometer. Compact and easy-to-align sensor heads and the possibility to use lightweight targets enable performance characterization even of small stages without high load.

A PICOSCALE sensor head assembly with three sensor heads in a pre-aligned mount is aligned to a light-weight 1 inch mirror. The mirror is fixed on a translation stage with an appropriate adapter. In the PICOSCALE Calculation System the signals of the three sensor heads are processed to directly output the pitch and yaw of the mirror

Closed-loop position control with interferometric precision

Accurate positioning of a sample is one of the core challenges in today’s high-precision manufacturing and research. The standard approach is to control the position using a high precision positioning system with integrated position feedback. However, the sample
can be mounted quite far away from the integrated sensor, so that possible drifts cannot be controlled with the desired accuracy.

The PICOSCALE Interferometer can be used to measure at (or at least very close to) the point of interest (POI). As the resolution and accuracy is typically far beyond that of linear encoders that use periodic patterns on glass scales, positioning of samples can be brought to a new level of precision.

Using the SmarAct SI interface, the position data can be directly sent to SmarAct’s modular control system MCS 2, which can use the data for direct and low latency feedback to control a SmarAct positioner.

Sound recording with a glass window

This application note depicts a proof-of-principle measurement on a glass window using a focusing sensor head. The glass moves on the nanometer scale due to acoustic exitation. For example, a human voice can be clearly identified in the displacement data. The data stream is directly streamed into a file and post-processing is straightforward.

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

 

Advantages of Michelson Interferometers

Michelson Interferometers have several advantages in terms of displacements sensing accuracy and flexibility.

Learn more in this article: Advantages of Michelson interferometers compared to other architectures

Specifications

 
PICOSCALE Interferometer
Resolution1 [pm] 1
Repeatability [nm] 1

Accuracy [nm]

Accuracy (length proportional)

3

10-6

RMS Noise [pm] 70*
Amplitude Spectral Density [pm] 1 @ 1000 Hz
Long Term Stability2 [nm} 1
Maximum Target Velocity [m/s] 2
Target Reflectivity 4% - 100%
Maximum Working Distance [mm] 1000
Absolute Position Estimation 1% of working distance

1 When analysing periodic displacements in the frequency domain

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