The materials from which we can make Fresnel and other lenses and lens arrays and related optics fall into several categories. This graph can be useful in determining which materials are appropriate in the wavelength range of interest for your application.
We offer optical quality acrylic, polycarbonate, and rigid vinyl for the visible light region. These materials transmit somewhat in the near infrared and in the ultraviolet as well; spectral details are available below. The use of rigid vinyl is discouraged for new applications in favor of thin polycarbonate, as rigid vinyl has many disadvantages and few advantages relative to polycarbonate. More details on these materials are available in our Fresnel Lenses brochure (652K PDF).
Fresnel Technologies, Inc. presently produces infrared transmitting Fresnel lenses in seven materials: POLY IR® 1, 2, 3, 4, 5, 6 and 7. Each has its own domain of applicability, and the materials are discussed in our POLY IR® Materials brochure (484K PDF). POLY IR® 1 material is an early attempt at a material for the 8 to 14 µm passive infrared range, and is no longer recommended for that use. However, it is superior to some other POLY IR® materials at shorter wavelengths, and may therefore be of some interest in applications other than passive infrared detection (and especially in multispectral applications). POLY IR® 2, 4, and 7 materials are recommended for use in the 8 to 14 µm passive infrared (PIR) region. POLY IR® 3 material offers superior performance and a practically flat spectrum for wavelengths longer than 12 µm. POLY IR® 5 material transmits well through the visible region to about 4.2 µm. POLY IR® 5 material contains no hydrogen, and so is free from the strong 3.4 µm absorption characteristic of hydrocarbons (and present in all our other materials). POLY IR® 6 material is a visible light filtering, infraredtransmitting material with a sharp cutoff in transmittance at about 780 nm.
Materials for the visible light region
Optical quality acrylic is the most widely applicable material, and is a good general-purpose material in the visible. Its transmittance is nearly flat and almost 92% from the ultraviolet to the near infrared; acrylic may additionally be specified to be UV transmitting (UVT acrylic) or UV filtering (UVF acrylic). The transmittance of our standard acrylic materials between 0.2 µm and 2.2 µm is shown in this graph for a thickness of 1/8" (3.2 mm). Standard acrylic thicknesses are 0.060" (1.5 mm), 0.090" (2.3 mm), and 0.125" (3.2 mm).
Polycarbonate is spectrally similar to acrylic, but is useful at higher temperatures and has a very high impact resistance. The transmittance of polycarbonate between 0.2 µm and 2.2 µm is shown in this graph for a nominal thickness of 1/8" (3.2 mm). Standard thicknesses available in polycarbonate are 0.015" (0.38 mm), 0.030" (0.76 mm), 0.050" (1.3 mm), 0.060" (1.5 mm), and 0.125" (3.2 mm). 0.015" and 0.030" are the preferred thicknesses for polycarbonate, unless an item cannot be molded in one of those thicknesses.
Rigid vinyl has a number of characteristics which make it both affordable and very suitable for certain applications. It has a high index of refraction; it is reasonably inexpensive; and it can be die-cut. However, polycarbonate has very similar properties, without the problems associated with rigid vinyl, and its use is encouraged over that of rigid vinyl in new applications. Rigid vinyl has about the same temperature range as acrylic and is naturally fire-retardant. The transmittance of rigid vinyl between 0.2 µm and 2.5 µm is shown in this graph for a nominal thickness of 0.030" (0.76 mm). Standard thicknesses for rigid vinyl are 0.010" (0.25 mm), 0.015" (0.38 mm), 0.020" (0.51 mm), and 0.030" (0.76 mm).
POLY IR® 1 infraredtransmitting material is a soft, flexible, whitish plastic. lts primary characteristics are reasonable transmittance in the 8 to 14 µm region, low index of refraction (and hence small reflection loss), and extremely low price. POLY IR® 1 is not ultraviolet stabilized, and must therefore be protected from the suns rays. The transmittance of POLY IR® 1 material between 0.4 and 40 µm is shown in this graph for a nominal thickness of 0.015" (0.38 mm).
The maximum contrast in emitted infrared radiation between a warm body (a human or a warmblooded animal, for example) and the slightly cooler background normally found indoors or out occurs in the 8 to 14 µm region. This is the basis for many clever consumer electronics devices, from convenience lighting to security systems. Inherent properties of the pyroelectric detectors used in these devices produce maximum signals for warm bodies moving against the background; proper lens array design can further enhance these signals. These passive infrared devices, so called because the natural infrared emission from warm bodies is used (rather than radiation from artificial sources), constitute a very important class of Fresnel lens applications.
A one-page listing of the available thicknesses and colors of the POLY IR® materials suitable for passive infrared applications is available here (48K PDF).
POLY IR® 2
POLY IR® 2 infraredtransmitting material is also a flexible, whitish plastic, but is substantially harder and more rigid than POLY IR® 1. It presently offers the least absorption loss in the 8 to 14 µm region of any of the POLY IR® materials. POLY IR® 2 material is ultraviolet stabilized, and has a lifetime of many years in full sun. (In our rooftop testing facility in the full Texas sun, wind and blowing dirt tend to cause damage long before the sun does; we have yet to establish a lifetime, though material which has been on the roof for two years shows no significant UV degradation in either infrared transmittance or physical properties. We also know of at least one instance of a PIR lens array in a passive infrared motion detector that has been used outdoors in Texas for approximately 15 years without a noticeable decrease in performance.) The transmittance of POLY IR® 2 material between 2.5 and 16 µm is shown in this graph for a nominal thickness of 0.015" (0.38 mm).
POLY IR® 4
POLY IR® 4 material is a pigmented version of POLY IR® 2 material. The pigmentation is not specifically intended as a filter for visible light, but rather as an aid in ultraviolet stabilization and for appearance. POLY IR® 4 material is available in a variety of colors and thicknesses. POLY IR® 4 material is ultraviolet stabilized, and has a lifetime of several years in full sun. There is no increase in transmission loss in the 8 to 14 µm region over that exhibited by POLY IR® 2 material for white POLY IR® 4 material, and minimal increases for the other colors. The transmittance of white POLY IR® 4 material between 2.5 and 16 µm is shown in this graph for a nominal thickness of 0.015" (0.38 mm).
POLY IR® 7
POLY IR® 7 material is also a pigmented version of POLY IR® 2 material, but it is pigmented to reduce false alarms due to white light. It is very effective in doing so, but shows an increased transmission loss in the 8 to 14 µm region of about 15 percent over POLY IR® 2 material or white POLY IR® 4 material. POLY IR® 7 material is available in a variety of colors and thicknesses. POLY IR® 7 material is not ultraviolet stabilized, and has an extremely short life outdoors (and an unacceptably short life in areas where sunlight entering windows or doors illuminates it). Dark grey POLY IR® 7 material has been used in some limited outdoor applications, but we do not recommend it. The transmittance of white POLY IR® 7 material between 2.5 and 16 µm is shown in this graph for a nominal thickness of 0.015" (0.39 mm).
This graph shows the transmittance of POLY IR® 2, 4, and 7 materials in the 8 to 14 µm region as a function of their thickness.
POLY IR® Materials for other applications
POLY IR® 3 infraredtransmitting material offers superior performance at wavelengths beyond 12 µm. The spectrum of POLY IR® 3 material is practically flat for wavelengths longer than 12 µm. POLY IR® 3 material is not ultraviolet stabilized. The transmittance of POLY IR® 3 material between 0.4 and 16 µm is shown in this graph for a nominal thickness of 0.020" (0.52 mm). Significant transmittance of POLY IR® 3 material in the 8 to 14 µm region occurs for wavelengths greater than 12 µm; the transmittance there is virtually independent of thickness.
POLY IR® 5 material contains no hydrogen, and so is free from the strong 3.4 µm absorption found in all hydrocarbon plastics materials. POLY IR® 5 material is suitable, for instance, for process monitoring at about 3.4 µm; it is clear in the visible as well. POLY IR® 5 material is ultraviolet stable. The transmittance of POLY IR® 5 material between 0.4 and 16 µm is shown in this graph for a nominal thickness of 0.030" (0.81 mm).
POLY IR® 6 material is a visible light filtering, infraredtransmitting plastic, used for near infrared (NIR) applications. These include near infrared (NIR) LED lighting for covert surveillance, active infrared presence detection, and near infrared communications in devices like remote controls and short range networks. The spectrum of POLY IR® 6 material has a sharp cutoff at a wavelength of about 780 nm; the material appears virtually black in visible light. The transmittance of POLY IR® 6 material between 0.3 and 2.2 µm is shown in this graph for a nominal thickness of 1/8" (2.8 mm).