Meaning
Precision distance measurement using the phase difference of split coherent light beams represents the highest standard of dimensional metrology in modern industry. Systems employing laser interferometry can resolve displacements down to the sub-nanometre range. This capability is essential for calibrating advanced machine tools and lithography equipment.
Measurement Principle
A coherent light source is split into two paths, a reference path of fixed length and a measurement path that tracks a moving target. When these beams recombine at the photodetector, they create an interference pattern of bright and dark fringes. Because the wavelength of the light is known and highly stable, laser interferometry determines the displacement of the moving target by counting these fringes.
Metrology Application
In coordinate measuring machines, this technology replaces physical scales to eliminate mechanical mounting errors. Using multiple interferometric axes allows the simultaneous measurement of linear displacement, pitch, and yaw. These measurements are recorded during factory calibration and are stored as compensation tables in the machine controller.
This calibration process ensures traceably accurate performance over the entire travel volume of the system.
Environmental Sensitivity
Changes in air temperature, pressure, and humidity alter the refractive index of air, which introduces measurement drift. Employing active compensation sensors that measure these parameters maintains the accuracy of laser interferometry during operation.
