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| Surface mapping Fizeau interferometer |
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| Product Highlights: |
| Fizeau interferometer |
- Measurement features:
- Able to accurately repeat measurements over a wide range
- Fast measurement and presentation of results (less than 7 seconds total)
- Environment monitoring waits for quiet period for best measurement
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| Software features: |
- Software monitoring of environment prevents corrupted measurements
- Advanced algorithms minimize measurement error due to vibration
- Complete, selectable RVA software analysis available
- Pentium based system insures compatibility and future upgrades
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| Physical features: |
- Stable, stiff rail structure allows measurements without the use of an air table
- Some mounts allow vertical testing
- Stress-free, repeatable mounting— no need for constant fine adjustment
- Total unit has a small footprint and is lightweight
- Horizontal or vertical operation
- Stabilized laser prevents light level variations, allows testing over long path lengths
- Easily integrates into automated process lines
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| An Overview |
| MiniFIZ is a laser-based instrument capable of sub-nanometer non-contact surface metrology. Featuring a modular structure, which allows customization to any application, MiniFIZ always reflects the highest standards of accuracy, durability, and speed. |
| MiniFIZ assesses flatness, sphericity and wavefront transmission. Special applications are already available for the optics industry: super-accurate testing of prisms, corner cubes, flats and radius of curvature. In the hard disk industry, flatness and static RVA analysis application options are used on high volume production lines for process control. |
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| A stable instrument for accurate and repeatable measurements |
| The compact design is stiff and stable, while its light weight and small footprint allow easy relocation. The optional rail set rigidly combines the holder mount with the interferometer. In many environments, this arrangement can be used without a vibration-isolation table. |
| The system has a high throughput which derives partly from the repeatability of the various optional holders. Samples place easily on the holder and maintain alignment. Tip-tilt adjustment to align the interference fringes is rarely needed, saving time. |
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| Environmental monitoring during measurement |
| Often a transient event will occur — such as a door closing — disrupting the measurement process. MiniFIZ monitors the level of vibrations affecting the fringe patterns and waits until the vibrations diminish to make a measurement. This ensures an accurate measurement. |
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| Full set of accessories and options |
| MiniFIZ's modular structure allows the purchase of a system tailored for every need. Choose from 50, 100, or 150mm (2", 4", and 6") apertures for a full variety of applications. Enjoy the flexibility of 100mm and 150mm apertures in one instrument with the 4 to 6" Aperture Converter Accessory. |
| Regardless of the option package, every MiniFIZ passes the same high standard of factory quality assurance -- so that you can see more detail, do more measurements, and do them faster than with any other system. |
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| Applications for this Products |
- Reflective disk flatness (RVA)
- Laser diode
- Flat optics
- Sphericity and radius of curvature metrology
- Wavefront transmission
- Fiber optic
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| Reflective disk flatness (RVA) |
| Runout, Velocity and Acceleration (RVA) application for the hard disk industry |
A powerful software package available with the MiniFIZ and OptiFLAT systems allows analysis of disk flatness, static run-out, velocity and acceleration. The analysis determines GO/NO-GO flags on parameters set by the user, so disk performance is quantified due to flatness variations. All measurement parameters can be output to spreadsheet files for user-defined statistical analysis to easily track trends in product. |
| The RVA screen can be configured to display the parameters needed to pass/fail a disk substrate. Failed specifications are highlighted in red. The circumferential plot can display 3 circular tracks at any user defined radius. Pass/fail specification can also be applied to those tracks. |
| Improving on RVA analysis, this application also offers tangential and radial curvature and slope to help further analyze and characterize disk substrates and media. |
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| Flat optics |
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| Surface flatness measurements |
| Flatness measurement interferometry setups such as this are used for the metrology of surface flatness of plano elements such as mirrors, prisms, and windows. |
| The transmission flat, which should be of known flatness and shape, serves to shape the beam to its own shape, and provides a reference wavefront which is compared to the returning, reflected light from the test object. Each spatial point in the combined beams is evaluated for the variation between the wavefront of the transmission flat and the test object. These differences are expressed as interference between the two beams. |
| The test object must be held so that the surface under test can be aligned in two axes of tilt. Using the two axis mount controls (or 'tip/tilt'), adjust tilt to optimize the number of fringes. When aligned, the interferometer monitor will display black, gray and white bands, known as 'fringes.' |
| If your MiniFIZ includes a zoom capability, zoom in or out from the test piece to make the object as large as possible in the test view, without clipping the image. This adjustment optimizes the lateral resolution of the measurement, essentially ensuring the largest number of data sampling points. |
| ADE Phase Shift also recommends using a phase-shifting MiniFIZ, which, combined with the power of a computer and our surface analysis software, will provide greater height detail, point-by-point in the data set. Flatness can be estimated by eye, if the user is experienced and trained; but precision measurements of the highest order require phase-shifting the interference fringes. |
| What you'll need for Surface Flatness testing: |
- Interferometer, phase shifting;
- Transmission flat, 4%;
- Mount, 2-axis (tip/tilt);
- Self-centering element holder.
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| Sphericity and radius of curvature metrology |
Each interferometer setup exampl e shows a MiniFIZ laser interferometer mainframe, a part being tested, and the optical accessories required to make the interferometry setup work. The accompanying text explains how the setup is used. |
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| Transmission Sphere Selection |
| Transmission spheres of various f/numbers are available as standard items, and others may be obtained on special order. If the speed (R/number) of the surface under test does not match the f/number of the transmission sphere being used, one of two situations will occur. If the R/number is smaller than the f/number, the interferogram will not fully cover the entire aperture of the surface under test. If the R/number is larger, the interferogram will be smaller than full size. However, the Mainframe’s f/number zoom can be used to bring the image on the viewscreen to full size over a 6X range in the latter situation. In order to select the optimum transmission sphere f/number to fill the aperture of a concave or convex surface, the R/number of the surface to be measured is calculated using the following formula: |
·R/Number= Radius of curvature of surface under test/ Clear aperture of surface under test
·Suggested Accessories: Phase Shifting Interferometer; Transmission flat, 4%; Mount, 3-axis; Self-centering element holder.
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| Concave Surface Figure - Sphericity |
| A transmission sphere transforms the Mainframe output beam into a precise spherical wavefront for the evaluation of spherical surfaces and lenses. A concave spherical surface is examined for surface figure and irregularity, i.e., the deviation from the best-fitting sphere, by placing its center of curvature coincident with the focus of the transmission sphere. Adjustment of the surface under test is typically provided by a 3-axis mount. |
Suggested Accessories: Phase Shifting Interfero meter; Transmission sphere; Mount, 3-axis (tip-tilt); Self-centering element holder.
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| Sphericity of Convex Surface Figure |
| Convex spherical surface are examined for surface figure and irregularity using the setup shown. In order to select the optimum transmission sphere, two criteria must be met. Firstly, the radius of curvature of the convex surface under test must be less than the back focal length of the transmission sphere; and secondly, the radius of curvature of the surface under test divided by the clear aperture, i.e., the R/number, should be approximately equal to the f/number of the transmission sphere. Six–inch diameter transmission spheres are available for this application. Adjustment of the surface under test is typically provided by a 3-axis mount. |
Suggested Accessories: Phase Shifting Interferometer ;Transmission sph ere, diverger; Mount, 3-axis; Self-centering element holder.
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| Radius of Curvature Non-Contacting Spherometer Radius and Figure |
| In addition to surface figure and irregularity, the radius of curvature of either a concave or convex spherical surface can be measured. The center of curvature of the test surface is interferometrically made to coincide with the focus of the spherical wave emanating from the transmission sphere. This is the location shown in the animation, in which the lens is farthest from the interferometer mainframe. Note that a concave test surface would invert the motion in this animation. In this arrangement, the fringe pattern provides information not only about the figure and irregularity of the surface under test, but also about the precise location of the center of curvature of the test surface with respect to the focus of that transmission sphere. The surface under test is then translated along the optical axis of the interferometer until the surface under test coincides with the focus of the spherical wave from the transmission sphere, as shown in the animation, when the hand introduces a card into the lightpath. This is known as the “cat’s eye” position. The fringe pattern again provides a very sensitive indicator of the point where the surface coincides with the focus. The distance that the surface under test is translated, Rx, is equal to the radius of curvature of that surface. The digital radius slide provides a convenient readout of this distance. This technique is typically accurate to 10microns or 0.1% whichever is larger, but precision is subject to the accuracy of the linear gauge. Contact customer support for a list of gauges compatible with ADE Phase Shift interferometers. For cases where extreme accuracy is required (1 micron or 0.001%) an Interferometric Radius Slide is available that inputs distance measurements directly to the interferometer’s processor and is corrected for focus errors. |
| The equivalent surface figure and irregularity and radius of curvature of a high quality spherical or cylindrical surface can be determined is a function of: |
a. The R/number of the surface under test.
b. The accuracy of judging fringe straightness.
c. The resolution and accuracy of the linear gauge.
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| Suggested Accessories: Phase Shifting Interferometer; Transmission sphere; Mount, 3-axis; Self-centering element holder; Linear gauge and slide mounting assembly. |
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| Choosing an Aperture Diameter |
Unlike plano surfaces, concave surface of any size can be examined in their entirety without depending upon the interferometer aperture diameter. This is accomplished by generating a diverging measurement wavefront of an f/number equal to, or somewhat faster than, the R/number of the test surface.
Convex surfaces, which must be placed in a converging measurement beam, may require a larger interferometer aperture. For convex surfaces of large size and/or long radius, it may be necessary to begin with a larger aperture converging beam produced by the appropriate transmission sphere. |
| ADE Phase Shift offers fizeau interferometers with apertures of 300mm, 150mm, 100mm, 50mm and 12.5mm to accommodate nearly any aperture requirement. |
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| Aperture Converters |
| ADE Phase Shift offers a 4inch to 6inch (100mm to 150mm) aperture converter. The converter accepts standard 150mm elements. The converter permits full resolution measurement of 150mm flats, and greater flexibility in measuring convex surfaces. |
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| Concave Surface Figure Measurement |
| Use a transmission sphere on the interferometer to bend the Minifiz output beam into a spherical wavefront for the evaluation of spherical surfaces and lenses. With this arrangement of optics, examine a concave spherical surface for surface figure and irregularity, that is, its deviation from a hypothetical best-fitting sphere, by placing its center of curvature at the point of focus of the transmission sphere. |
| Radius of curvature can be determined with some additional accessories. Check the sphericity page for an illustration of this process. |
| Adjustment of the surface under test is typically provided by a 3-axis mount. |
| Using phase shifting, the interferometer acquires data about surface height variations. Note that concave surface measurements of this type effectively remove the spherical surface figure, and 'see' the curved surface as virtually flat. This then allows an analysis of the test surface's departure from sphericity, by showing local shape variations. |
| Suggested Accessories: Phase Shifting Interferometer; Transmission sphere; Mount, 3-axis (tip-tilt); Self-centering element holder. |
| Below are links for other interferometer setups, for measuring different kinds of surface figures. |
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| Wavefront transmission |
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This setup is used to measure distortion of a plane wave transmitted through the article under test. It is typically used for windows, filters, and prisms. In addition, glass and other transparent raw material may be examined for homogeneity evaluation. Since the measurement beam passes through the article under test this article need only be placed nominally perpendicular to the optical axis of the test beam. No special mount or alignment is required.
Suggested Accessories: Phase Shifting Interferometer, Transmission flat, 4%; Mount, 2-axis (tip-tilt); Reference flat, 4%. |
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