Rocky Mountain Instrument Co.

Tech Notes » Getting Started

In this section, we outline the major considerations for choosing the right optical substrate for your specific application. Every type of optical material possesses unique properties that are valuable in different circumstances. The goal is to find the most affordable substrate that delivers the best performance for your specific application. Some of the important questions to ask when selecting an optical substrate are:

What is the wavelength or wavelength region of my application?
Some applications require only a single wavelength, such as Excimer, YAG or CO2 lasers. Other applications require transmission in multiple regions, such as a combination visible and infrared system. In the case of IR applications, effective heat dissipation and conductivity is a factor when selecting a substrate. Reference our Material Data charts for more detailed information on transmission regions, refraction indices, and useful wavelenth regions for the most common optical substrate.

What is the power level of my application?
As the power level of the application increases (i.e., in high power laser applications) choosing a low absorption substrate becomes a critical factor to the longevity and performance of your optic.

Does the optic need to hold up under extreme environmental conditions?
Even if two substrates have the similar optical characteristics for a given wavelength or region, they can respond differently to various environmental conditions. Thermal shock, extreme temperatures, and reaction to humidity are some of the conditions to be considered.

Does the optic need to hold up under extreme physical conditions?
Although some substrates may have similar optical characteristics, they can behave differently depending upon various physical/mechanical conditions. Environments where vibration, mechanical shock or other recurring stress are a factor may require more durable substrates which, by nature, may also be more difficult to fabricate.

What is the availability of a particular substrate?
Some substrates, including BK7, fused silica, and most other types of optical glass are readily available in a wide variety of sizes, making them much more cost effective. On the other hand, some substrates such as magnesium fluoride and barium fluoride become exponentially expensive for sizes larger than 2" in diameter. At such sizes, there are only a few raw material vendors in the world who provide the substrates.

How easy is the substrate to fabricate?
Some materials are easy to process and achieve excellent surface quality while other materials are fragile, easy to damage, or very difficult to achieve good surface quality. In general, fluorides (MgF2, CaF2, and BaF2), being of a crystalline structure are more difficult to fabricate than glasses (BK7, fused silica) which are homogeneous.