How is AR coating measured? What Method Can You Use

how is ar coating measured

Do you know what an AR coat means? It is a thin, transparent layer of material that people use for lenses and other optical components.

A reflective coating comes with a special design to increase light transmission while minimizing unwanted reflections. It means you do not have to worry about glare or ghosting when you are trying to see things with bright lights shining through. 

Yet, How is AR coating measured? In this article below, we will show you in detail some popular methods to measure AR coating. Keep reading and check it out now!

UV-Vis Spectroscopy

There are many ways to test the performance of an anti-reflective coating. One popular method is using UV-Vis spectroscopy. It is a device that uses reflection measurements and absorption measurements on the tested surface to provide a way to evaluate the performance of materials with low and high levels of reflection. 

Besides lense, you can also use a UV-Vis spectrometer on various materials, like laser mirrors, LCD screens, or other devices. Still, in order to perform the test, you will need to have a specular reflectance attachment or an absolute reflectance attachment in hand. 

When doing the test on AR coating or any other materials, there are some details you have to notice since absolute and relative specular reflectance can have some subtle differences in measurement data. 

In particular, absolute reflectance provides absolute values in measurement so there is no need for conversion or calculation. Meanwhile, measured data by relative reflectance is a corresponding value. This is because it has to take the value of the reflecting process on an aluminum mirror as a reference. 

Even if you use the same material, the results will still be different with relative reflectance. This is since the reference's reflectance is never 100 percent, and the values are frequently influenced by the wavelength employed. The values typically are 80 to 95 percent of the absolute ones. 

Therefore, measurements will differ from what you would get with absolute measurement data. However, when consistently using the same reflectance mirror, the outcome will be repeatable; thereby, reducing the variance greatly.

Threshold-Shift Method

Another method to be used in measuring AR coating is Threshold-Shift Method. This method mainly measures high-relative components or thin films with only 10-3 optical thicknesses. 

It uses mathematics to assert the relationship between the laser length and the threshold current before and after the applied time of the coating. Therefore, you need to know the data of the gain index, laser length, coating parameters and the refractive index to execute this method perfectly.

If someone told you that this method could be performed without the data of coating parameters, it is true. However, you must spend more time measuring and performing more complex steps than when having all the information needed. 

Once having all the equations and parameters, you can get the result of the reflectivity coating based on the variation of the threshold current measured before coating application and those obtained after coatings are applied. 

Conclusion

We hope that after reading this article, you know “How is AR coating measured?”. There are many ways to perform the measurements, including UV-Vis spectroscopy and the threshold-shift method. This is why we have brought them up in this article. 

These two do have some notes that you need to keep in mind as you proceed so mark them down carefully to avoid any problems. If you have questions regarding this topic, feel free to leave us a comment and we will get to you as soon as possible.

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