www.zygo.com Strengthen | Expand | Grow Introduction to Displacement Measuring Interferometry Outline Displacement measurement Basics of Displacement Measuring Interferometers (DMIs) Common interferometer configurations Introduction to uncertainty sources Specialized interferometer configurations Some application examples Summary 2 Some terms that are used throughout this presentation DMI Displacement Measuring Interferometer OPL Optical Path Length OPD Optical Path Difference f Split frequency ppm Parts per million = multiplier of 1 X 10-6 ppb Parts per billion = multiplier of 1 X 10-9 3 www.zygo.com Strengthen | Expand | Grow Displacement Measurement What does ‘displacement’ mean in this context? Denotes a change in position How far something has moved Implies a Start point and an end point Relative motion Distinguished from ‘distance’ Absolute separation between two points Displacement measurement tools can establish distance indirectly 5 Distance and displacement are two different things! Target Retroreflector Two-frequency laser Cannot measure distance from beamsplitter! 6 Can measure displacement of target Another example of the distinction between distance & displacement Transparent artifact whose length needs to be determined Direct measurement of length is not possible with DMI Indirect measurements are possible by measuring displacement of a probing mechanism 7 Consequences of relative nature of measurement If the beams of a DMI are broken and signal is lost, system loses track of target position When beam is reestablished, system starts counting from current position of target System has no knowledge of the new position relative to the beamsplitter Critical that beam not be interrupted! 8 ‘Absolute’ interferometers exist Absolute measurements can be performed interferometrically Based on different working principle Multi-wavelength Frequency sweeping Tutoria