Questions You Should Know about Single layer magnesium fluoride coating

Interactive Tutorials

Antireflection Surface Coatings

The concept behind antireflection technology is to control the light used in an optical device in such a way that the light rays reflect from surfaces where it is intended and beneficial, and do not reflect from surfaces where this would have a deleterious effect on the image being observed. One of the most significant advances made in modern lens design, whether for microscopes, cameras, or other optical devices, is the significant improvement in antireflection coating technology. This tutorial explores various coatings and their reflectivities as a function of incident angle.

For more information, please visit CLZ.

The tutorial initializes with a monochromatic (red) wave of light incident on the surface of a coated lens at a 50-degree angle. The Incident Angle slider can be employed to vary this value between 10 and 90 degrees. As this slider is translated, the percentages of light reflected from (Total Reflection), and transmitted through (Total Transmission), the lens are presented above the slider. The Top Layer and Bottom Layer pull-down menus can be used to select the materials employed for reflectivity calculations in the tutorial. Note how changing these values affects the reflectivity of the surface coating layer pair.

Thin coatings of certain materials, when applied to lens surfaces, can help reduce unwanted reflections from the surfaces that can occur when light passes through a lens system. Modern lenses that are highly corrected for optical aberrations generally have multiple individual lenses, or lens elements, which are mechanically held together in a barrel or lens tube, and are more properly referred to as a lens or optical system. Each air-glass interface in such a system, if not coated to reduce reflections, can reflect between four and five percent of an incident light beam normal to the surface, resulting in a transmission value of 95 to 96 percent at normal incidence. Application of a quarter-wavelength thick antireflection coating having a specifically chosen refractive index can increase the transmission value by three to four percent.

Modern objective lenses for microscopes, as well as those designed for cameras and other optical devices, have become increasingly more sophisticated and complex, and may have 15 or more separate lens elements with multiple air-glass interfaces. If none of the elements were coated, reflection losses in the lens for axial rays alone would reduce transmittance values to around 50 percent. In the past, single-layer coatings were used to reduce glare and improve light transmission, but these have been largely supplanted by multilayer coatings that can produce transmittance values exceeding 99.9 percent for visible light.

Illustrated in Figure 1 is a schematic drawing of light waves reflecting from and/or passing through a lens element coated with two antireflection layers. The incident wave strikes the first layer (Layer A in Figure 1) at an angle, resulting in part of the light being reflected (R(0)) and part being transmitted through the first layer. Upon encountering the second antireflection layer (Layer B), another portion of the light (R(1)) is reflected at the same angle and interferes with light reflected from the first layer. Some of the remaining light waves continue on to the glass surface where they are again partially reflected and partially transmitted. Light that is reflected from the glass surface (R(2)) interferes (both constructively and destructively) with light reflected from the antireflection layers. The refractive indices of the antireflection layers differ from that of the glass and the surrounding medium (air), and are carefully chosen according to the composition of the glass used in the particular lens element to produce the desired refraction angles. As the light waves pass through the antireflection coatings and the glass lens surface, nearly all of the light (depending upon the angle of incidence) is ultimately transmitted through the lens element and focused to form an image.

Magnesium fluoride is one of many materials used for thin-layer optical antireflection coatings, although most microscope and lens manufacturers now produce their own proprietary coating formulations. The general result of these antireflection measures is a dramatic improvement of image quality in optical devices because of increased transmission of visible wavelengths, reduction of glare from unwanted reflections, and elimination of interference from unwanted wavelengths that lie outside the visible light spectral range.

The reflection of visible light is a property of the behavior of light that is fundamental in the function of all modern microscopes. Light is often reflected by one or more of plane (or flat) mirrors within the microscope to direct the light path through lenses that form the virtual images we see in the oculars (eyepieces). Microscopes also make use of beamsplitters to allow some light to be reflected while simultaneously transmitting other light to different parts of the optical system. Other optical components in the microscope, such as specially designed prisms, filters, and lens coatings, also carry out their functions in forming the image with a crucial reliance on the phenomenon of light reflection.

Contributing Authors

Robert T. Sutter and Michael W. Davidson - National High Magnetic Field Laboratory, East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, .

Regarding the use of magnesium fluoride, many applications can be mentioned. The fact has shown that this combination of magnesium and the element fluorine, due to the special ion form it forms, shows surprising and sometimes even contradictory properties. The applications of this material are so wide that even in many industries that are not related to each other, we see the use of magnesium fluoride. In this note, another type of application of magnesium fluoride is targeted and we plan to plan and review the key features related to it. As you can guess from the title, this time we will go to the use of magnesium fluoride in anti-reflection coating. To begin with, of course, we begin with a summary of the nature of anti-reflection coatings. Stay with us until the end.

If you want to learn more, please visit our website Single layer magnesium fluoride coating.

What is anti-reflective coating and what is its function?

Anti-reflective coating, known in English as (Anti-Reflective Coating) or abbreviated (AR Coating), is one of the most practical phenomena in the field of optics and optical devices. This coating, as its name suggests, after being sprayed and placed on any surface, suppresses or in other words reduces the amount of light reflected from that surface. Usually, in the design of various optical devices, including lenses, mirrors, glass protectors and buffers or any other essentials in the field of optics, anti-reflection coating is sprayed on the outer wall of the object and at the point where it meets the surrounding air. For example, in the camera lens, an anti-reflection coating is placed on the outer part of the lens that will be towards the subject. Now the question is, what is the main purpose of using anti-reflective coating?

Pay attention to the difference in the shape of light reflection from the surface of the upper and lower glasses; This shows the application of magnesium fluoride

The fact is that the answer to this question is closely related to the form of application of magnesium fluoride in anti-reflection coating. Due to the special properties of magnesium fluoride, this layer reduces the reflection of certain light spectrums from the surface of the lens, for example. For this reason, the minimum amount of light is reflected and repelled in contact with the surface of the lens. As a result, more light penetrates into the lens and in this way the loss of light is reduced due to undesirable reflections from the surface of the lens. Or, for example, in mirrors, if the outer glass of the mirror, placed in front of the layer of mercury or any other reflective metal, passes all the light with maximum efficiency, as a result, the quality of visible images will increase. In general, it can be said that the anti-reflective coating improves the efficiency and productivity of optical tools due to the properties of magnesium fluoride, and in tools such as lenses, it noticeably increases the natural and vivid contrast of the image. In many optical devices and essentials in the field of optics, even the smallest disturbing and undesirable reflections may disrupt the entire use of the device. Now, the question is, in what tools is the anti-reflection coating used?

Camera lenses that have this feature are ideal for night and low-light photography

Where does the use of anti-reflective coating stand out?

As mentioned in the previous section, the fact is that parallel to the wide application of magnesium fluoride, the anti-reflective coating itself has a very wide application and is used in various areas related to light. The main application of this type of coating is related to optical and light devices. A special anti-reflective coating is used in camera lenses, telescope lenses, slit cameras and binoculars, the surface of some types of mirrors with special applications, and even on the surface of the lens and glass of glasses. So, in general, wherever there is a need to remove annoying reflections and increase the percentage of light penetration, magnesium fluoride stands out with its use in making this type of coating.

Sometimes a layer of it is drawn in contact with a layer of (SiO2) on the glass

How does magnesium fluoride help the anti-reflective coating work?

The application of magnesium fluoride in anti-reflective coating comes from the refractive properties and special reaction of this material to light. In some types of Single Layer AR Coating, magnesium fluoride is used as a Broadband AR Coating. This means that a layer of this material is sprayed on the surface during a special process and in contact with visible light, it absorbs and transmits a wide range of different wavelengths with minimal reflection. According to the available data, while the ideal index for the production of such anti-reflection tools is the refractive index of 1.23, with only one layer of magnesium fluoride, the refractive index of 1.38 can be achieved and a significant improvement can be made. For example, if a layer of magnesium fluoride with a thickness of 0.145 micrometers is sprayed on the surface of a normal glass, the percentage of light reflected from its surface will decrease from 4% to only 1%! The reason for this is the better passage of at least a quarter of the wavelength of green light in the middle of the visible band, which has helped the use of magnesium fluoride in the anti-reflection coating.

The company is the world’s best Spherical Lenses supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.