09
AUG
2016

IRG Educational Series: Infrared – The Light We Cannot See

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Electromagnetic radiation is all around us. We can see part of it (known as the “visible spectrum”) as the sun shining, the green of tree leaves, or the warm yellow glow of a light bulb.  But there are many forms of electromagnetic radiation around us every day that are invisible to our eyes.

photo credit (above): modified infrared photography Pedro Fernandes CC BY 2.0

 

The Electromagnetic Spectrum

The electromagnetic spectrum showing the breakout of UV, visible, and Infrared (IR) light

The electromagnetic spectrum showing the breakout of UV, visible, and Infrared (IR) light

Our eyes can’t see ultraviolet light from the sun, but it sunburns our skin. We can’t see the infrared radiation from the stove, but our hand can tell that it is hot. Microwaves remain invisible, even as they cook our food in the kitchen. Radio waves carry all of the WiFi information transmitted between our laptops and the Internet, and they travel through walls and windows to do so.

We describe this radiation as traveling in waves. Just as red, blue, and green light are visible colors, different only in their wavelength (or frequency), UV, Infrared, Microwave, and Radio waves are all different “colors”–it’s just that our human eyes can’t see them.

The image above shows some of the electromagnetic radiation that we experience in our world–short, energetic Cosmic rays from space and long, lower energy Radio waves. This radiation can be transmitted, reflected, absorbed, scattered, or refracted when it interacts with objects. It can even be emitted from objects or focused. This means we can control and detect the various types of radiation and use it in some pretty amazing ways.

The electromagnetic spectrum: how light interacts with matter

 

The Infrared Region of the Electromagnetic Spectrum

Infrared regions of the electromagnetic spectrum that are transparent in air

Infrared regions of the electromagnetic spectrum that are transparent in air

Like the different colors of the rainbow, the infrared (or IR) part of the electromagnetic spectrum has several useful wavelength bands (measured in micrometers, or μm) where the infrared light can pass through the atmosphere without encountering water or carbon dioxide. These important transparent regions are known as “windows.” These windows are known as the Shortwave-IR (SWIR 0.7 – 2 μm), Midwave-IR (MWIR 3-5 μm), and Longwave-IR (LWIR 8-12 μm) regions.  Each region is important in different applications.

Infrared astronomy: learning more about the Universe

 

Infrared Imaging

Infrared radiation is the color of light put out by warm bodies. Infrared imaging is the process of making some of these invisible regions visible to humans. If you have ever used a pair of night vision goggles, or seen pictures of heat leaking out of your single-paned windows, you have experienced infrared imaging.

Infrared imagers use detectors and windows that are tuned to the IR portion of the spectrum, and convert that image to visible colors that we can see. Some of important applications that use infrared imaging include  night vision surveillance , fire and marine heat imaging, and industrial inspection.

SWIR imaging applications

 

Materials for Infrared Applications

Students at the University of Central Florida test the infrared transparency of a piece of chalcogenide glass.

Students at the University of Central Florida test the infrared transparency of a piece of chalcogenide glass.

There are several materials that are used for infrared applications. Any application that needs to transmit or focus infrared light needs a material that the IR light passes through. IRradiance Glass products, made out of chalcogenide glass, are transparent to infrared (or IR) light. Many chalcogenide glasses don’t allow visible light to pass through (most have a silver, metal-like appearance), but they are transparent in the important window regions of the infrared spectrum we talked about above. IRradiance Glass makes industry-standard glasses for optics used in the these IR regions as well as custom-designed materials that are best suited for a particular purpose in a specific infrared region.

Healthcare application: glucose sensing using mid-infrared light

 

We want to hear from you.  Help us make our education series something that you want to learn more about. We’ll be providing information for both students and those with extensive industry experience. Please send us your comments and questions in any of our social media forums.  Conversations on LinkedIn, Facebook, Twitter.

About the Author
IRradiance Glass, Inc. (IRG) is a manufacturing, research and product development company, specifically focused on the compositional design and hot forming of chalcogenide glasses.