To those who have little knowledge about optics, the place of mirrors may seem a little uncertain. After all, we know for a fact that optics are about lenses, so what is the point in working with broadband mirrors and, even more than that, with metal mirrors? Read on and you will be surprised to discover the wide range of utilities that these elements actually have.
Just like lenses, mirrors have the purpose of reflecting the light. From simple illumination or imaging processes to interferometry and beamsteering, optical mirrors have a tremendous utility. Consequently, they have become essential devices in all kinds of industries, solar, semiconductor, life sciences, metrology and astronomy included!
Those who really know how to master such environments build flat or laser, focusing or with metal substrates and even specialty mirrors, all of which supporting or including all sorts of coatings. If metal coatings for lenses have the purpose of controlling the reflective properties of an environment and rescuing the light waves, metal mirrors do the opposite.
After all, a lens absorbs light and processes images while a mirror reflects light and reproduces images. In consequence, no matter what type of coating is applied to a certain mirror, the result would be to increase the reflectivity so that the desired wavelength to be perceived by that mirror. Take laser mirrors as an example, their coatings are especially optimized in order to match with a laser’s wavelength.
Back to our metal mirrors, they usually find their utility inside applications that demand constant and even expansion of the thermal coefficient, in between the mirror and the base mount. If they have one of the two surfaces concave, they make the perfect pick for catching applications based on light focusing.
Even so, we have not approached so far the issue of broadband mirrors. These can easily compete with the previously mentioned laser mirrors, only that their manufacturing process involves adding multiple layers of coating. As a result, these optical devices provide an incredibly high reflectance not just on p-polarizations, but also on s-polarizations, supporting an even larger wavelength. Basically, broadband units support broader wavelengths – do you get the association?
If you want numbers to indicate you the difference between the simple and the broadband units, it would be enough to specify how a broadband background provides 99.5% higher results than the average coatings. And yes, these mirrors can be enhanced by receiving a metal coating, hence the term of metal broadband mirrors.
Aside from the metal coating, you may often hear of dielectric coatings, which are known to provide a narrower, smaller spectral range. In the end, metal layers have one of the highest reflectivity when compared to the widest spectral ranges. The number of combinationss that can result, with applications to IR, VIS and UV spectral regions, is quite overwhelming. Lucky for you, now you know at least the basics about all these.