Optical flats combined with a coating coupon for perfect results
First of all, as a subdivision of physics responsible with studying the properties and behaviors of light when interacting with various environments, optics makes a fascinating science. It studies anything from visible to ultraviolet and even infrared wavelengths and it serves to tens of different fields, all of which expecting exact results. Have you ever wondered how perfection is achieved? Perhaps a coating coupon or resorting to optical flats will bring some light…
If you feel confused about what these two notions mean, think of them as two instruments of measuring the effectiveness of an optical surface and getting to witness quality before actually purchasing a product. To be more specific, an optical flat is an incredibly smooth surface that serves as point of reference. The equivalent of spirit level in masonry, a flat device reveals how neat a mirror, a lens or anything else related really is.
As you can imagine, perfectly even surfaces are essential when trying to guide the path of a fascicle so that to generate a certain result. Summarizing, it takes us to a precisely, close to perfectly polished surface that indicates the flatness of another surface, through comparison. When the optical flat gets in contact with another surface and monochromatic light is directed toward the system, the existing gaps or unevennesses will show up as interference fringes.
The accuracy of the measurement is reported to fractions referred to a particular wavelength set at 632.8 nm. Otherwise said, you get to choose from several accuracy levels: 1/4, 1/10 or 1/20, where 1 is the equivalent of the previously mentioned reference wavelength. 1/20 would therefore mean that the maximum difference of level in between the irregularities of the measured surface is of 632.8/20, meaning 31.64 nm.
As you can imagine, from testing the quality of mirrors, prisms, windows, filters and lenses to inspecting gauge blocks, optical flats are highly useful. Speaking of quality and testing, a coating coupon is nearly just as important. The term is also often referred to as a witness sample and it makes the proof of conformity and performance of an optical coating. Again, by extension to masonry, a coupon is like the paint sample that you look at before deciding what concentrated paint to buy for your home renovation!
Instead of directly ordering the coated mirrors or lenses, a customer can order a coupon and make himself a better idea of what he is about to purchase. Going further into details, these samples can be simple coating coupons or laser grade coupons. Those from the first category may have certain imperfections, like chips for example, but only on the outer side of the so-called clear aperture. Those from the second category however are way more rigorous and must provide precisely the same degree of quality as the final product.
Of course, there are many other ways of evaluating the performances of different optical units, but these two are the ones you are most likely to bump into. The next time when you will interact with a manufacturer or seller, make sure you mention them in your discussion.
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