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Fizeau Interferometer

Non Contact Flatness measurement Interferometer also called Fizeau Interferometer for inspection of flatness of optical or mechanical parts. Many Mechanical seal manufacturer use this Interferometer for evaluation of flatness. In Automobile parts many flat surfaces require inspection of flatness in light bands. Monochromatic Light source and use of Optical Flat is replaced with Fizeau Interferometer.


  • Technical mass products with flat surfaces specified to better than 0.1µm over a few cm are produced by millions per month.
  • The production processes are lapping & polishing – and, increasingly more often, micro-machining; 90% have diameters under 50mm.
  • ISO 9000 requires tight inspection often 100%.
  • The most common tool for this is The Interferometer
  • An esteemed value to engineers as does the stethoscope for the medical practitioner.

Interferometer is shown in Figure 1 (The basic layout of a Fizeau Autocollimator). A laser source is spatial y filtered via a microscope objective. This microscope objective is located at the focal point of a collimating lens. Between the microscope objective and lens is a cube beam-splitter. The collimated beam encounters a slightly wedged glass plate. This is the heart of the interferometer. The surface adjacent to the collimating lens is of good optical quality.

However, the next surface is of exceptional optical quality, λ/20 peak to valley (PV) or better. This is the reference surface and part of the collimated beam is reflected by this surface. Part of the collimated beam continues on to interrogate the component being tested. The return beam contains information on aberration introduced by the test surface. The two wave fronts recombine inside the interferometer.

The cube beam-splitter diverts the combined beam towards a recording medium, either film or a CCD. An intermediate lens forms an image of the test surface onto the recording plane.


Model FAC-25 FAC-60 FAC-100
Orientation Vertical Vertical Vertical
Light Source- He-Ne Laser < 2 mW < 2 mW < 2 mW
Clear Aperture 25 mm 60 mm 100 mm
Reference Flat λ/20 λ/20 λ/20
Work Table (Tilt Table) Dimension 3" x 3" 4" x 4" 6" x 6"
1/2" CCD Camera 640 x 570 pixels 640 x 570 pixels 640 x 570 pixels
Viewing : Alignment and Fringe viewing Yes Yes Yes
Dimensions : L x B X H 300 x 250  x 470 300 x 250 x 570 300 x 250 x 800
Weight 27 Kgs 38 Kgs 55 Kgs