Tech Briefs Magazine - May 2021 - PIT-4

						
SWIR Line Scan


	



V

isible light is only a tiny part of
the electromagnetic spectrum.
Gamma rays, X-rays, ultraviolet, infrared, microwave and
radio waves each have their own unique
properties and their own place in the
spectrum. In this article, we'll focus on
SWIR, or short-wave infrared, which is
one component of infrared (IR) light.
Infrared wavelengths are those below red;
the word " infra " is Latin for " below. "

SWIR Imaging Defined

certain materials become more or less
reflective, and more or less transmissive
in the SWIR vs. the visible. For instance,
silicon becomes transparent beyond ~1
μm, but water actually becomes more
absorptive in the SWIR - especially
around bands at 1.45 μm and 1.8 to 2 μm.
This means colors that appear almost
identical in visible light can be easily differentiated in the SWIR.

How do SWIR Vision Systems
Work?
SWIR cameras are often built around
Indium Gallium Arsenide (InGaAs)
infrared detectors. InGaAs sensors can
be made extremely sensitive, and as a

panuwat phimpha/Shutterstock.com

As humans, we experience infrared
light as mostly invisible, but we can feel
it as heat. The IR spectrum is divided
into different regions, and each region

has different applications. The four
commonly referenced regions are near
infrared (NIR) with wavelengths of 750 1,000 nm, short-wave infrared (SWIR) at
1 - 3 μm, medium- or mid-wave infrared
(MWIR) at 3 - 5 μm and long-wave
infrared (LWIR) clocking in at 8 - 15 μm
(Figure 1).
Except for the fact that you can't see it
with the naked eye, SWIR is like visible
light in that photons are reflected or
absorbed by an object. This is unlike midwave and long-wave infrared light, where
heat is emitted from the object itself.
SWIR imaging can highlight " defects " in
an inspection that visible imaging cannot.
When imaging in SWIR, water vapor and

4

Photonics & Imaging Technology, May 2021

Cov

ToC


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Tech Briefs Magazine - May 2021

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