High accuracy point diffraction interferometer
High accuracy point diffraction interferometery
Industrial point diffraction interferometery
point diffraction interferometer
point diffraction interferometry
absolute surface form
optical metrology


Difrotec has developed a breakthrough technology in optical testing

The D7 is phase-shifting point diffraction common path interferometer for ultra high accuracy measurements of surface form and transmitted wavefront quality.

The D7 detects the absolute figure of a surface or wavefront. See video

Absolute figure means that the measured form is counted from the absolute reference i.e. perfect spherical wavefront produced by diffraction of light by a sub-wavelength aperture.

7 Values of D7.pdf


Peak-to-valley absolute accuracy: ± 0.7 nm (λ/900)

Peak-to-valley resolution: 0.05 nm (λ/12000)

Wavefront RMS repeatability: < 0.25 nm (λ/2500)

Simple RMS repeatability: < 0.06 nm (λ/10500)

Laser type and wavelength: stabilized He-Ne, 632.8 nm

Numerical aperture NA: 0.55 (f# 0.91)

Data acquisition: phase-shifting interferometry (PSI)

Measurement schemes

1. Spherical concave surfaces:

2. Spherical convex surfaces:

3. Flat surfaces:

4. Optical systems (wavefront quality testing):

More detailed description of measurement options you can find here:


optical testing & Measurements

Optical testing and measurement services include testing surface figure of concave, convex, corner cubes, flat, aspheres, freeforms, and transmitted wavefronts of optical systems, and also measurements of curvature radius. (test your optics)

Optical design & fabrication

Based on over 30 years experience in computer modeling of high precision optical systems, we have established our own partnerships to design and manufacture high quality optics. Our long-term partner in optics fabrication is KPU - Korea Polytechnic University.

Test your optics with the D7

Contact our CTO to discuss the details about your request
Send your optics to us at Teaduspargi 13, 51014 Tartu, Estonia
We will measure it and send back with detailed report
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