Plano (flat) Optics
Single sided plano optics are ground and polished on one side only. These flats are frequently used as “test plates,” or reference surfaces, to which the flatness of other optics or substrates is compared. Plano references are typically made from extremely stable materials such as fused silica, BK7 glass, Zerodur, Zinc Sulfide, Germanium, Sapphire, Silicon or Zinc selenide. A single sided optic may also serve as the substrate for a high-quality optical mirror.
Dual sided plano optics, or double-sided plano optics, are polished to specification on both sides. A double-sided optic may be used as an optical window (with two parallel surfaces), a wedge (with the two surfaces polished at a small angle relative to each other), as a substrate for an optical filter, as a material sample to test homogeneity, or as a reference for evaluating another test optic.
In the most general sense, plano optics include all components with a surface that can be tested using a collimated beam to compare it against a flat reference. By that broader definition, the family of plano optics can be said to also include beam splitters, corner cubes, prisms, periscopes, etalons for spectroscopy, etc.
4D’s dynamic Fizeau laser interferometers measure flatness, shape, thickness uniformity, homogeneity and wedge of plano optics, mirrors, windows, wedges, wafers, filters, etc. 4D Fizeau systems are available to measure flat optics at wavelengths from deep UV through IR.
The compact AccuFiz Fizeau excels at fast, repeatable measurement of surface shape and transmitted wavefront error of flat and wedged optics. With the optional Surface Isolation (SIS) module the AccuFiz can measure both sides of transparent, parallel optics as thin as 200 microns, as well as surfaces in multi-surface optical systems, remote cavity test setups, and solid cavities.
Beam Expanders allow a standard AccuFiz system to measure optics with diameters up to 800mm, including solid state laser optics and high energy laser amplifier slabs.
NanoCam Sq systems measure surface roughness on coated and uncoated plano optics to ensure the quality of polishing processes.
Homogeneity is a measurement of how much a specific glass optic’s refractive index deviates across its substance. Using our dynamic, short coherence interferometers, you can measure homogeneity more easily with three, not four, measurements. Plane-parallel flats without wedge can also be measured.
Parallelism is a measurement of how well aligned the two faces of a flat are to each other. For many optics, a wedge angle between the front and back surface is deliberately created to prevent the two surfaces from interfering. Both parallelism and wedge can be measured on 4D interferometers. Parallelism is particularly easy, using our short coherence source.
Added Technical Resources
Setting the Wedge Factor
This tech note explains the purpose of the Wedge Factor and its correct values for measuring wavefront error and surface height in common testing configurations.
Measuring Transmitted Wavefront Error
The FizCam 2000 dynamic interferometer enables vibration insensitive measurement of plane-parallel optics, remote cavities and large convex mirrors.
Measuring Homogeneity with AccuFiz
Spatial inhomogeneity of an optic’s refractive index can be caused by the melting process, by variations in density or by permanent stresses due to temperature gradients during cooling.
Products for Plano (Flat) Optics
Excels at fast, repeatable measurement of surface shape and transmitted wavefront error of flat and wedged optics. It is the most versatile Fizeau available, for any production environment.
Measures both sides of transparent, parallel optics as thin as 200 microns, surfaces in multi-surface optical systems, remote cavity test setups, and solid cavities such as etalons (laser rods).
NanoCam Sq systems measure surface roughness on coated and uncoated flats to ensure the quality of polishing processes.