Laser interferometric measuring systems

Laser interferometric measuring systems are based on the interference of two or more laser beams and represent a tool for the measurement of distances and other geometrical quantities. The scale of their potential application is very broad, and they may be used for the measurement of short distances in the range of millimeters or over meters or tens of meters. However, the primary resolution is in the range of tens of nanometer.

Systems designed at ISI are used for:

• the measurement of the position of three-axis positioning stages;
• the calibration of scales of a broad range of various position sensors;
• measurements of the refractive index of air.

Examples of applications:

• Interferometry for nanometrology. Nanometrology is based on the imaging of samples using techniques of local probe microscopy, primarily Atomic Force Microscopy (AFM). When the scale of the objects in the nanoworld has to be measured the positioning of the AFM probe must be measured through interferometry with a direct link to the primary etalon of length (stabilized laser). The setup for measuring the probe is derived from a nanopositioning stage and a system of interferometers monitoring the sample position in three or even all six degrees of freedom. The local probe microscope is placed over the sample. The limits of uncertainty of the measurements are given by the mechanical stiffness of the whole setup and by the fluctuations of the refractive index of air. The resolution is below 1 nm.
• Precise positioning systems and comparators. Interferometric systems designed at ISI can offer resolution at the 0.1 nm level, i.e. the resolution of interatomic distances. Practical applications of these positioning and measuring systems are in the field of scale calibration of various position sensors used in industrial measurements.
• Measuring of the refractive index of air of gaseous media. At the ISI laboratories we are also involved in the development of measurement techniques for the refractive index of gasses. We operate two systems for evaluation of the refractive index of air that can be used to measure any other transparent media, liquids and solid materials.
• Interferometry with compensation of the refractive index of air. An arrangement with differential measurement allows compensating the influence of variations of the refractive index of air. The basis of the configuration is a mechanical reference with very small thermal expansion, and the wavelength of the laser source is locked to its length through the sum value of the two counter measuring interferometers.