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Precision Displacement Measurement via a Distance Measuring Interferometer (DMI)

Precision Displacement Measurement via a Distance Measuring Interferometer (DMI). Why DMI Is Needed. Important characteristics of ``International Technology Roadmap for Semiconductors: 2001'' published by the SIA. Laser. IF. Electronics. Receiver. General System.

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Precision Displacement Measurement via a Distance Measuring Interferometer (DMI)

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  1. Precision Displacement Measurement via a Distance Measuring Interferometer (DMI)

  2. Why DMI Is Needed Important characteristics of ``International Technology Roadmap for Semiconductors: 2001'' published by the SIA.

  3. Laser IF Electronics Receiver General System • DMI system is comprised of three parts: • IF • Laser • Electronics

  4. DMI History

  5. Michelson Interferometer • Michelson-Morley experiment (c.a. 1887). • Typical use of the Michelson interferometer is to compare a test optical surface against a known high quality reference flat. The output of the measurement is a light fringe pattern viewed from a diffuse surface. These fringes are spatial fringes.

  6. Laser I Heterodyne Photodetector Michelson Interferometer, Using Polarized Light

  7. Single Axis Interferometer10706B Plane Mirror IF

  8. Multiaxis IF10735A

  9. Design ConsiderationsCNC Protective Covers

  10. | | | | | | | | 0 5 10 15 20 25 30 35 Frequency (MHz) Design ConsiderationsSplit Frequency Limit on Velocity For a four pass plane mirror IF.

  11. Design ConsiderationsMiscellaneous • Vacuum compatibility. • Low adjustability. • Beam size. • Metric vs. U.S. Customary. • DCTE between parent structure and IF parts. • Peak-to-Valley (PV) wavefront per optic. • Remote Receiver fibers (bend radius).

  12. L0 DMI System ErrorsDeadpath & Environment Deadpath: Difference in physical optical path between Reference and Measure. Therefore, in this example the deadpath is L=4L0. This is assuming that the air space between the PBS and the two quarter wave plates are equal.

  13. DMI System ErrorsDeadpath & Environment • Edlen’s Equation Metrologia, Vol. 2, No. 2, Pg. 71, 1966 • Air Temperature, T (°C) • Barometric pressure, P (mmHg) • Relative humidity, H (%) • Gas composition. Typically not measured. or , therefore

  14. DMI System ErrorsAbbe Error Abbe error can be eliminated through with a q measurement, and by knowing L.

  15. DMI System ErrorsCosine Error • Reduced through proper alignment. • Part of the accuracy budget, and not the repeatability budget. • As an example, you can expect a 10706B to have a cosine error of 0.05 ppm (50 nm for a 1 m travel).

  16. DMI System ErrorsErrors Summary • Make the ambient environment tightly-controlled and stable, and apply atmospheric compensation tools. • Minimize deadpath distances and Abbe offsets, and subtract in the processing. • Properly align the optics.

  17. Summary • DMI is currently the most accurate and sensitive linear translation measurement scheme. Additionally, it has a near limitless translation measurement bandwidth. • Relative, not absolute. • Noncontact. • Near coaxial measurement of translation axis. • Resolution (Agilent 10897B electronics and two-pass IF): 1.2 nm. • Accuracy: ~2-3 nm. • Max. range: > 10 meters. • All 6 DOFs of a rigid body, are indirectly measurable. • Max. velocity (two-pass IF): 2 m/s. • Typical beam diameters: 3, 6 and 9 mm. 9mm is preferred.

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