1) Aerospace and Defense Imaging
-
Reconnaissance: Spy satellites have a large primary mirror which enables the identification of an individual person or model of a car, or whether a missile is fueled and ready for launch- all from orbit. One important advantage lies in its steerable secondary mirror, which allows the satellite to quickly switch its view between different targets, truly being the ‘digital eyes’ of our defense system.
- Deformable mirrors are used to correct for atmospheric distortion, controlled by tiny pistons behind an array of individual, smaller hexagonal mirror segments. Interferometry verifies that the mirror reacts accurately to the electrical signals for ‘correct’ distortion.
- Targeting systems: Lenses and mirrors in night-vision goggles and laser guided “smart” weapons must be precisely polished for clear imaging. The windows on the lasers themselves must be flat and homogeneous, both measured with interferometry.
2) Semiconductor Manufacturing
- Wafer flatness: Silicon wafers must be tested for flatness using interferometry before the microchip patterns are ‘printed’ onto them using photolithography. Local form errors in a wafer can cause the microchip patterns to blur, resulting in areas of failed chips.
- Mask and reticle Inspection: The reticle is the ‘master blueprint’ through which light is projected to print each patterned layer of a microchip. If the reticle has form errors, printed features will be out of focus, resulting in failure.
- Projection optics: The lenses used to project these patterns must have extremely low transmitted wavefront error for all the same reasons. These must be measured using interferometry
- Computational Lithography: The most advanced photolithography machines use interferometry to characterize the wavefront error, which is then canceled out with a ‘deformable’ optical layer in the projection path!
3) Network Communications
- Starlink uses a network of mirrors to relay signals around the earth. Each piece must meet form and roughness requirements.
- Telecommunications uses optics
4) Medical Technology
- Medical imaging: The small imaging lenses inside medical devices, such as an endoscope, are tested using interferometry to ensure crisp, undistorted views of the tissues.
- Intraocular lenses: Tested using interferometry to ensure the patient will regain 20/20 vision after undergoing cataract surgery.
5) Astronomy and Space Exploration
- Space Telescopes: Interferometry is the ‘gold standard’ for the high-precision measurement of telescope mirrors, such as those used in the James Webb and Hubble telescopes. The primary mirror is the largest which ‘catches’ the light, while a smaller, secondary mirror redirects it to an eyepiece or imaging system. Telescopes in space are more limited in size since they must be portable.
- Ground Telescopes can have much larger primary mirrors, but they have to overcome one very large obstacle: an ever-changing environment. Environmental fluctuations introduce wavefront error from the distant star or planet being viewed. With primary mirrors that are deformable, those wavefront errors can be cancelled to reveal a crisp, clear image!
5) Astronomy and Space Exploration
- Space Telescopes: Interferometry is the ‘gold standard’ for the high-precision measurement of telescope mirrors, such as those used in the James Webb and Hubble telescopes. The primary mirror is the largest which ‘catches’ the light, while a smaller, secondary mirror redirects it to an eyepiece or imaging system. Telescopes in space are more limited in size since they must be portable.
- Ground Telescopes can have much larger primary mirrors, but they have to overcome one very large obstacle: an ever-changing environment. Environmental fluctuations introduce wavefront error from the distant star or planet being viewed. With primary mirrors that are deformable, those wavefront errors can be cancelled to reveal a crisp, clear image!
6) Automotive
- Interferometry is used both on the production line and in the laboratory.
- Form measurement: Interfometry is used to measure the flatness of sealing surfaces under high pressure, such as cylinder heads and fuel injector valve seats. If a surface that should be flat has waviness of just a few nanometers, it can lead to fuel or other fluid leaks, resulting in blown head gaskets and poor fuel economy.
- Roughness measurement: The inside of a cylinder bore is checked using white light interferometry to ensure it has a specific roughness, rather than be perfectly smooth. Why? – the inner wall has a pattern of micro-scratches intended to hold a certain amount of oil for optimal lubricaton. If the surfaces are too smooth, the piston can have a squeegee effect on the inner wall, causing metal-to-metal contact and overheating the engine. can overheat. Cylinder bore surfaces that are too rough can also cause metal-to-metal contact, where the peaks of the microscratches scratch the cylinder wall, above the layer of oil. White light interferometry is used on the production line to check this roughness, and engineers use it to study the wear of these components in order to design more fuel-efficient engines with less friction.
7) General Manufacturing
This is the ‘catch-all’ category of applications outside of those previously mentioned. The most common are listed below.
- Very small ‘microlenses’ are used in more applications than just medical and defense. Microlenses are used to focus light onto sensors in smartphones, to couple light into fibers for telecommunication, and focus light for microsidplays, to name a few. These are measured for form using large aperture interferometers, and for waviness and roughness using white light interferometers.
- For any applicaton that requires a transmissive optic, homogeneity of the glass is crucial to achieve distortion-free imaging. This can only be measured using interferometry.