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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Working in the Infrared Bands

Matching optics to extended wavelengths can increase clarity, offer greater transmission and improve contrast
Figure 1
© StingRay Optics
Figure 1: An optical designer will select suitable lens materials for a design based upon their locations on a chart like this one.
Figure 2
© StingRay Optics
Figure 2: The anti-reflectance coating charted here is optimized to keep the reflectance of light between 425nm to 680nm below 1 percent per surface.
Figure 3
© StingRay Optics
Figure 3: This image and that in Figure 4 were taken in series in series. Figure 3 was taken with a visible lens and Figure 4 with a specialized SWIR lens.
Figure 4
© StingRay Optics
Figure 4: The same image as Figure 3, but taken with a specialized SWIR lens.
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By Christopher Alexay

For the past several years sensor manufacturers in the photonics marketplace have met many technical challenges to yield new arrays, detectors and entire camera systems that expand our understanding of light and imaging. The latest technologies offer exciting advances that explore imaging using portions of the electromagnetic spectrum that go beyond the limits of human visual perception.

Newer detector technologies now offer the opportunity to produce images from light wavelengths that range from the visible region of the spectrum out to portions of the infrared. These wide spectral bands designated as shortwave infrared (SWIR), near infrared (NIR) and/or visible-near infrared (VNIR) will be the focus of our discussion on the important role optical design plays in achieving higher sensitivity and clearer imagery in these extended wavelengths.

Application-specific Optics

Work at StingRay Optics has been conducted with a variety of end users whose research involves these spectral ranges. The company has discovered a common grievance among end users regarding the image quality of some of the VNIR/NIR and SWIR imaging systems. The customer expects and requires a camera system to work in these extended wavelengths with optimal sensitivity and image clarity. However, many of these specialized camera systems are configured with optics or lenses that are not well-suited for rendering quality imaging in these spectral ranges.

Until very recently, integrators and, in some cases camera manufactures, have indicated that their VNIR/NIR/SWIR imaging products are capable of using the wide variety of lenses designed for use in visible photography or similar applications whereby the designed region of operation rarely extends beyond the visible wavelengths. These lenses offer an attractive option in that they are abundant, off-the-shelf and available at low cost. Produced in high volumes, the lens cost is only a small fraction of the camera package price, an appealing marketing feature, indeed.

However, the shortcomings in these inexpensive and often inadequate lenses for the VNIR/NIR/SWIR wavelengths, and the subsequent frustration voiced from customers, has prompted StingRay to develop alternative solutions—namely lenses that optimize performance at these wavelengths with enhanced resolution and sensitivity.

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