Many optical systems require transparent windows for various reasons. These windows can safeguard a system from external hazards and provide environmental and vacuum seal to the system. A designer must be aware of several factors when designing an optical window for a system such as strength, transmission, durability and available coatings.
The first of all, it is important to determine the quantity for optical windows, so as to evenly distribute the funds. One should keep in mind, the larger the quantity of the pieces, the less expensive will be each part as cost can be divided over total number of parts.
Select the material
This is an important consideration. For this, one needs to consider the features of the materials as well as application needs. There are many different types of materials used for optical windows based on the purpose of any application. Magnesium fluoride window is an optical window manufactured from hard, durable optical material lends itself well to use under harsh conditions. Similarly, Sapphire optics are an ideal material for applications where high pressure, vacuum, or corrosive atmospheres.
There are many different types of materials used for designing optical windows such as N-BK7®, fused silica, quartz etc. One needs to consider the features and capabilities of the materials and application requirements to make the right choice.
Determine/ selecting the shapes
Optical windows can be made in different shapes such as round, rectangular, square etc. The round shape is considered as the best choice for obtaining flatness/accuracy. These windows can also be made in custom shapes to provide more challenges to maintaining surface flatness. Proper mounting of the window is necessary to ensure that window is sealed from outside environment.
Define your mechanical tolerance
Before choosing an optical window, one should define the acceptable limits of both size and thickness required for an application. For instance, if optical window is made in round shape, one should provide tolerance for diameter. If it is in rectangular/Square, one should provide tolerance for LxW.
Density
The density of the optical window is important due to its correlative effect on light refraction. Also, it correlated to weight/. The denser the material, the more will be the weight. When you are designing an optical window where weight sensitivity is critical, one needs to use less dense material.
Coatings
Coatings are important aspect of optical windows. These coatings are selected on the basis of the operating environment and the desired wavelength of the system. In optical systems that operate over a wide range of wavelength, a broadband coating is necessary.
Knoop Hardness (kg/mm2)
Knoop hardness of the material is an important consideration for manufacturing optical window. One should bear in mind that if a material has a high Knoop hardness, it is generally more robust and can withstand greater pressure shocks. The lower the number, the more brittle will be the material of the window.
Windows are crucial component in nearly all optical systems. These windows provide a transparent barrier from outside environment. Most manufacturers provide a range of optical windows such as selenite, calcium fluoride and Magnesium fluoride windows. Most of them also offer a range of anti-reflection coated optical windows to improve the transmission from UV to IR wavelength regime. Once you consider all the factors needed to select optical windows, you can get them fabricated and manufactured in a variety of custom sizes, shapes, and substrates.
