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Concepts in Light and Optics – Requesting an Optic

Posted by Bill Hill on

Ordering a custom optic, Concepts in Light and OpticsWe continue our discussion through the basic concepts of light and optics by making a detour away from the fundamentals and instead focusing on an often undiscussed aspect of our field – how to request an optic. This article is directed to the procurement specialist, college student and any individual who needs an optical component but has very little experience in contacting an optical supplier for a specific need. Perhaps you were tasked with finding a window or directed to purchase a lens with a 100mm focal length and simply don’t know where to begin. Our goal is to offer a reference to assist you in finding the most appropriate optic for your application in as little as time as possible.

Often times at Esco we receive inquiries that generate more questions than answers. In fact, this is a near daily occurrence. Through repetition, we’ve found that in order to understand a customer’s requirements, we generally ask many of the same questions and, by simply offering a few additional details up front, a solution is almost always readily available. For example, as noted above, it is not uncommon for us to receive a request for a lens with a defined focal length but with no further information. Ordering a custom opticsWhile this is a good starting point, it presents a vast array of choices that may be fulfilled from one of our stock product lines (or perhaps move into the realm of a custom optic) but we simply don’t know since we have no idea how the optic is being used or how it is installed in your system. By providing details that address the optic’s dimensions, spectrum of use, application and environment, as we as, expected performance including the possible addition of thin film coatings, you can avoid the back and forth dialogue that may take days to resolve, delaying your procurement and schedule.

Dimensions

Surprising to us is the number of inquiries we receive that lack information regarding the size of a customer’s required optic. Whether a diameter or rectangle, without the basics of size and tolerances, determining any further details, let alone cost, is impossible. If the optic in questions is a lens, information on any restrictions in center or edge thickness is important to begin the process of finding the appropriate match. If unknown, refer back to how the optic is mounted in the system to better understand the required final configuration.custom optical window, prototype optic

Material & Spectrum

We tie these two aspects of optics together because not all materials are created equal, both in performance and cost. If you are unfamiliar with the electromagnetic spectrum, we encourage you to read our article Essential Concepts in Light and Optics for a better understanding of how light works. That said, if you’re pressed for time, we can break down the spectrum into three simple optical regions and letting us know your areas of interest will help narrow down your choices of material considerably. Your regions may overlap somewhat, but don’t worry, a lot of materials do as well so we can recommend what may work best for you. What follows are generalities and not considered true scientific definitions – consider them a guideline.

Ultraviolet:  250nm – 400nm 

These are wavelength below the visible spectrum where fused silica reigns supreme. If you are working below 250nm, still considered ultraviolet, we will need to know more about your application (see section below) as this region moves into some highly specific optical materials requiring special considerations.

Visible:  400nm – 750nm

There are literally hundreds of materials to choose from in this range, however, there is also a reason why Esco’s stock product line of windows is kept simple with the choice of standard optical glass (BK7), fused silica/quartz, low expansion (Borofloat) and sapphire. These four material variations cover the vast majority of applications and optical environments that may be encountered when working in the visible region. Usually it simply comes down to the consideration of cost in relation to performance and durability.

Near Infrared / Infrared: >750nm

This is the region above the visible spectrum most commonly associated with the detection and imaging of heat signatures. It is important to specify because many of the materials that work in the visible and ultraviolet regions no longer transmit light above a certain defined wavelength. They essentially “shut off” and offer no functionality.

Application & Environment

custom optic questionsThis section could literally become a full article in its own right, but our goal is to keep things simple. In short, when requesting an optic, offering a few details on how it will be used will provide us almost all the information we need to present a solution. Is it an imaging application and, if so, what are you imaging? Is it a basic viewing window that only requires transparency? Will you be directing a laser through the optic (see section on lasers below)? Having covered hundreds of different applications over Esco’s 60+ years in business, we’ve probably come across a similar, if not exact request for optics used in your setup. Let our expertise be your guide by letting us know the basics of how it’s used.

Environment is also important because not all materials withstand the rigors of exposure to harsh conditions. Are there temperature considerations? Will the optic be exposed to moisture, salt, caustic chemicals or excessive handling? Perhaps the optic is used in environments where extremely low or high pressure is a concern. Again, providing a few details on these type of factors will help us narrow down the available choices of materials and specifications.

Optical Specifications & Performance

Esco’s commercial optics are specified to approximately 5 waves in surface form and for most basic applications, this is sufficient for functionality. For more complex systems, determining functionality without the assistance of an optical designer or engineer is difficult and we always prefer a drawing of the optic to assist in providing a quotation, especially if it is a custom configuration. Unfortunately, optical specifications can be quite complex and if you are uncertain of how to specify your optic we recommend reading our articles on how optical surfaces are characterized (Lenses Part 2 & Plano Optics). If you still are unsure how to proceed, an Esco sales representative can assist in determining how precise your optics may need to be by understanding the details of dimensions, application/environment and the spectrum in which it will be used. Please contact us directly for further assistance and we can take you through the steps of characterizing your optic.

Lasers

Lasers deserve their own consideration because not all optics are made to withstand the level of power density some lasers can generate. You need not understand how lasers work but there is no guarantee of functionality or longevity without the following details:

Type/Wavelength: What kind of laser are you using and what portion of the spectrum does it operate? For example, a common laser type is the Nd/YAG (Neodymium-doped / Yttrium Aluminum Garnet) which produces a beam of light at 1064nm. Understanding the type of laser is very important in determining the appropriate material. Also of interest is the power rating of the laser, specifically whether the laser is pulsed or continuous.

Pulsed Lasers: These laser can generate an incredible amount of power and cycle billions, if not more times per second. The output power is specified in joules or millijoules per square centimeter, written mJ/cm^2 or J/cm^2 and this information is important when requesting an optic for use in the lasers path. The second characteristic is the physical spot size or, more simply, the actual diameter of the laser beam.

Continuous Lasers: Continuous lasers, as the name implies, are laser that have a continuous output of power. Their power rating is specified in watts or milliwatts per square centimeter, written mW/cm^2 or W/cm^2. Please specify the power rating when using a continuous laser.

Coatings

Optical thin film coatings, like application and environment, could warrant its own article, but for the novice, we can breakdown the requirements one simple parameter – spectrum. Coatings are designed to function over specific regions of the electromagnetic spectrum and we need to know where to optimize the design.  Coatings used with lasers are also specially designed to withstand the intense power in order not to fail in the system. By specifying application, environment and the possible use of lasers, you’ve already covered a large portion of the information we need to determine what type of coating works best.

Summation

As we’ve described above, a request that does not specify the dimensions, application/environment, spectrum or performance expectations leaves us without the appropriate tools to determine which optical configuration is required. By adding a few extra details to your inquiry, you will save valuable time and assist us in providing a solution that places an optic in your hands as fast as possible. And to make your procurement even easier, we’ve added a new online inquiry page that covers all of the aspects listed above. With a few clicks of your mouse, you can send a request with all required info directly to the Esco sales team where we’ll be happy to locate the most appropriate optic for your application. We look forward to hearing from you.

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