Things to Consider When Ordering Optical Flats
Optical flats, also known as “test flats”, “test plates” or “reference flats” are precisely polished surfaces that are used to measure the flatness (surface accuracy) of an unknown surface. They do so by using the property of interference.
When optical flats are placed on a test surface, an air wedge forms where the two surfaces don’t touch. The thickness of the air wedge is analyzed to find out the shape and direction of the interference bands, which helps in determining the flatness of the test surface.
When viewed under monochromatic light, the two surfaces show light and dark bands, called interference fringes. If these interference fringes are parallel and straight, the test surface will be said to have more than or equal flatness compared to the reference surface. Conversely, an uneven interference pattern shows that the test surface’s flatness is lesser than that of the reference flat.
Common flat optical components used in the IR, UV and visible spectrums are:
· Filters
· Wedges
· Mirrors
· windows
· Waveplates
· Encoder disks
· Debris shields
· Reference surfaces
· Light pipes
· Gratings
Factors to Consider
Here are some factors you need to consider when ordering optical flats:
Optical Material
Homogeneity, bubbles, and stress birefringence are some of the most important factors since they affect product performance, quality, and pricing.
For instance, an optician’s ability to achieve the desired transmitted wavefront specification goes down as the product’s homogeneity decreases. Similarly, stress birefringence impacts the mechanical stability of the test surface. Bubbles, on the other hand, can affect the product’s cosmetics during the polishing and grinding stages.
Best optical materials for single and dual surface flat optics are BK7 and fused silica. While other materials can also be used, they require special processing techniques and careful handling as they might be sensitive to humidity or temperature.
Wedged or Parallel
Components like plate beam splitters, filters, windows, and wafers typically need to be of high parallelism, whereas wedges and prisms may be intentionally wedged.
Factors like polishing and grinding play a crucial role in achieving the desired parallelism specifications. Double-sided polishing and grinding are one of the best methods to achieve exceptional parallelism (i.e. <1 arc second). Manufacturers measure parallelism using an interferometer.
Conversely, prisms and wedges are processed using pitch polishers to achieve the required angled surfaces.
Dimensions
Although optical flats are of various shapes, round optics are the best in achieving desired specifications uniformly and quickly.
If you need to customize optical flats, get in touch with Tower Optical; they’re a leader in customizing high-quality precision optics with over 20 years of experience in the industry.
They also offer a variety of products, including optical filters, optical flats, beam expanders, laser mirrors, and more than 10,000 waveplates.
Send in your drawing and specifications and they’ll reach out to you with a quotation!