How IR X-Ray Vision Works
"Reflected" IR X-Ray See-Through Vision
you are wondering what makes this ability possible. The answer lies in
infrared rays. All reflected light that we can see with the naked eye
represents a fractional portion of the electromagnetic spectrum, which is
infinite. We refer to this section as "visible
light". All around us, light is reflected which the human
retina cannot detect, such as ultraviolet and infrared radiation.
The visible part of the spectrum falls between the wavelengths of 430nm~690nm.
have much larger wavelengths than this. We divide them into
"Near Infrared Rays" (690nm-4,000nm) and "Extreme Infrared
Rays" (over 4,000nm).
Unlike ultraviolet and visible rays, infrared rays
tend to penetrate any medium rather easily because of their large wavelengths. This
also means that infrared rays are not refracted much at all when passing from
one medium to another. When we shine sunlight through a prism, it is
refracted at an angle according to its wavelength. The blue end of the visible
spectrum has the shortest wavelength, so is refracted the most. At the
other end of the spectrum, beyond the red, visible light, infrared rays
are barely refracted at all because of their long wavelength.
The KAYA PF exploits this characteristic of infrared
light. It only lets through these long-wavelength rays, which have low
refractive rays, and not all the ultraviolet and visible rays. Here's how
this relates to the mannequin experiment:
- Light Source
- Infrared Rays
- Ultraviolet and Visible Rays
- KAYA PF Filter
- CCD Camera
Almost all of the ultraviolet and visible rays are unable to permeate the
fiber and are reflected back instead. Conversely, almost all of the infrared rays can
easily permeate the material due to its low refractive rate. Having passed
through the cloth, the infrared rays fail to penetrate the mannequin's surface
and are reflected back.
The PF is struck by ultraviolet & visible rays that
are reflected from the cloth and also the infrared rays that are reflected
from the mannequin's surface. But the PF only lets the infrared rays pass through. The
infrared rays are then transformed into electrical signals by the CCD of a camera,
which forms those signals into a visible-light image.
In conclusion, the observer will be able to view the
scene as though infrared light has become visible.
Of course, if you were to simply look through the PF, you
would not see anything at all. Remember, the PF lets through infrared
light only, which is invisible to the human eye. Therefore there must be
some media, or device, installed to detect and record, or convert, the
image. As mentioned previously, camcorders and digital cameras are suitable devices
for this purpose because they employ a CCD which responds to both visible
and infrared light.
Strictly speaking, it would be more accurate to
regard these "See-Through" pictures as "near-infrared
images" rather than "infrared images" since almost all CCDs can only respond
up to 1400nm. Thus from hereon we shall use the term
"near-infrared", or "NIR" when talking about the
images the PF allows.
"Fluoresced" IR X-Ray See-Through
principle of Fluoresced IR X-Ray See-Through Vision is very different to the Reflected
IR X-Ray See-Through Vision principle
some substances are illuminated by certain wavelengths they reflect back not only
those same wavelengths but also they may transform some of
these into other, usually longer, wavelengths. For example, some substances may transform
the illuminating visible light energy into
longer-wavelength infrared energy.
What causes this phenomenon? The answer
can be found in
atomic physics and quantum mechanics. Within atoms, electrons orbit about a
central nucleus. If a packet of light energy (a "photon") is absorbed by the atom,
it causes one of the electrons to move out to a wider orbit. As described by
quantum mechanics, atoms will only ever absorb radiation which has the right amount
of energy to make one of the electrons perform this "quantum leap" to
the next electron "shell". A photon's
energy is dependent on its wavelength (and therefore, its colour), with violet being higher
energy than red. However, an atom with an electron out of place is not stable
for long so the electron falls back, re-releasing a 'photon' of energy. Some energy is lost so the photon given off is shifted towards the red end of
the spectrum compared with the one absorbed.
A Fluoresced See-Through
image is slightly more difficult to achieve.
Besides the PF filter, an Infrared Cut Filter ("ICF") is required to
create one. This filter performs the exact opposite task to the PF - it
lets through visible light but cuts all infrared light from passing
through. To capture a Fluoresced See-Through image, the ICF is placed over the light source to limit the incident light and prevent any infrared
rays emitted by the source from reaching the subject. Some
of the visible rays, which remain, striking the subject are changed to longer, invisible infrared
rays and then the PF filter allows only these newly created infrared rays to pass into
the camcorder or digital camera.
This Fluoresced See-Through
technique often reveals
characteristics of a subject that are not readily apparent through
other examination methods including Reflected See-Through. For example, chlorophyll
in plants does not reflect
infrared rays, but it does fluoresce. This may provide a means for studying certain
plant diseases. Similarly, this technique can be used for the study of inks, hardwoods,
forged documents or paintings and sometimes startling results can be obtained.
To take more effective Fluoresced See-Through pictures, note the suggestions
||If possible, total
||KAYA's ICF1 over the
This is not required if there is another way to
ensure the subject is only illuminated by visible light. For
example, wavelength-tunable lasers or blue-green lasers are ideal.
Wavelength-tunable lasers have the advantage of being able to easily
select from a wide range of wavelengths.
||PF1 or PF2