There is more to light than the visible spectrum. [What is Infrared light ?]

Watching movies is really what I enjoyed doing. But I don't just watch anything, I watch action packed movie, something that glued me to the screen until the last scene lapsed. For instance, i love to watch films where special agents on mission are to break through top secret government facility or a highly secured placed.

Most times, these special agents will have to break through some security technology system like a laser security system which uses an alarm Unit that works with Infrared motion sensors. The Infrared motion sensors operates by detecting heat emitted from the body of these guys. The detected heat by the Infra-Red sensor then triggered the alarm Unit. The system subsequently alert security personnels on duty. The high pitched alarm sounds triggered with the siren blowing do infuriates me, especially if I want those guys breaching the security system to have what they are hunting for.

In one of the action packed movie I watched recently, it happens that some guys had information about whereabouts of an artifact, knowing quite sure that it's well secured they went ahead. The last entrance to where the artifact was kept was protected with a laser beam door which consists of a laser pointer the source of the light beam. Their amateur tech expert was the first to interrupt the laser part which triggered the alarm. He actually intended to deactivate the laser transmitter which is powered by a 3V direct current supply located at one side of the door frame. If he had deactivated the source, the receiver which contain a photo transistor at the other end will not sense any Infrared beam anymore and they would have carried out their hideous act.

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Much talk about movie, you said right ?, but you shouldn't stopped there. In this write up, I intend to discuss about infrared light which is part of the electromagnetic spectrum. It's of wide application in various field be it laser technology, [the introduction], thermal imaging camera, remote sensing, medicine, applied sciences, astronomy, military, forensic and many more.

Infra-Red light application is wide because it brings into illumination what would have never been seen under the visible region of electromagnetic spectrum; ( very low temperature body {cold body} to be discussed later).

I will start with laser, so let's tightening our seat belt and start the trip.

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What is LASER ?

Laser is an acronym for Light Amplification By Stimulated Emission Of Radiation which can be said to be a tool that discharge light in a process of optical amplification which depends on the stimulation of emitted electromagnetic radiation.

By Paul Hirst (Phirst) - Own work, The twin Keck telescopes CC BY-SA 2.5,

Laser uniqueness can be attributed to it's consistency in emitting light when compared to other light source. It's spatial coherence or consistency permit it to be focused on a fixed spot, an ability it possess which qualify it to be applied in laser cutting and in lithography. With it ability to be consistent in space without scattering over long distance, it find application in laser pointers.

Another property it possess is the temporal coherence. This permit it to discharge light at a very narrow spectrum ( emitting light at a single colour).

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Light is not just about the visible region

When an average person even well learned hear about light, the first thing that comes to mind is the visible light which enter the eyes and stimulates vision such that things in the surroundings could be seen clearly.

Though visible light is an electromagnetic radiation between the infrared and the ultraviolet light of the electromagnetic spectrum which ranges from the gamma-ray to the radio waves. The light is the only visible region out of all the electromagnetic radiation present in the spectrum. We can see our physical surroundings because of the visible region on the spectrum which has wavelength within the range of 400–700 nanometres (nm). Human eyes can only see anything within this region.

However, light is beyond the visible portion of the spectrum. There are several objects that remains invisible within this region, because their temperature is low and the heat they radiate is not within this range of wavelength, so they remain invisible. However, some objects that have their temperature close to room temperature only radiate heat which corresponds within wavelength of the Infra-Red region, so they become visible within this region under specialized condition. Infrared has wavelength ranging from 700nm to 1m

Light beyond the visible -----> INFRARED RADIATION.
As earlier discussed, it's part of the electromagnetic spectrum, it has low frequency, low energy and of course, longer wavelength which means it is not that energetic when compared with gamma or ultraviolet radiation known to be highly energetic.

Infra-Red radiation has tremendously helped various field of interest in sciences, astronomy inclusive. Astronomers in their study of celestial objects had used optical telescope (using visible light) and have been able to come up with some result.

But in seeing some celestia bodies or Stars covered by dust, their ordinary optical telescope which operates within the visible region of the electromagnetic spectrum became limited, because within the visible region of the spectrum, only objects with higher temperature radiates thermal energy that correspond to the visible region wavelength. The dust provides a shield impenetrable by the visible light of the telescope; the dust are not transparent to the optical telescope. However, working at near-infrared those stars becomes visible because the Infra-Red will be able to detect the emissions coming from the stars and if at far-Infrared, emissions even from the dust that cover the stars will be detected and those stars become visible.

All objects emitts thermal energy (wavelength different)

They become visible because of the Infra-Red radiation they emitts. There is no object that do not emitts heat no matter how little the heat might be. You can think of anything, your pet dog, a cat, melting ice, a vehicle and even you. [Recently, @alexdory wrote post on heating your home with cat; it was a beautiful post ]. What this means is that most objects gives out heat. Though heat energy emitted may differ. The heat energy emitted by some bodies is of several hundreds of Kelvin while some are of few hundreds of Kelvin. Objects with few hundreds of Kelvin emit their internal heat at infrared wavelength. But it's quite impossible to sit down withing the visible region to see what is happening in the Infra-Red region of the spectrum. You need an eye aid to see how things goes.

Infra-Red radiation is not just for the astronomers. In several military night operation, (visible light is useless here) may be they are approaching enemy territory or even during a search and rescue operation, thermal infrared imagers are good eye aid to see into thick darkness clearly.

The imagers are detector in combination with lenses which then gives a pictorial representation of emitted radiation from the body in the dark.

The thermal imagers employed law of conservation of energy because it never create a new energy, but transforms the detected Infra-Red energy to an electronic signal which produce a thermal image.The mode of operation of the thermal image camera is similar to how visible light camera operate. Just that the lens of the thermal imaging camera collect and focus Infra-Red wave emitted from a body to the Infra-Red sensor array. Several thousands of sensors changes the infrared energy to electrical signals. The electrical signals are what is seen as an image.

Cold objects/ bodies gives off infrared too.

Like I earlier put, every object you could think of radiate heat, however, the amount of heat given off depends on the body temperature. The heat given off is in form of infrared light. For instance, a very hot body put out more infrared radiation than a cold body would give off. A hot body glow brightly when compared with a cold body.

For instance, the image shown to the right is the infrared image of the mixture of hot and cold water. You can see some part glowing brightly yellow while the other part is a bit purple. The yellow glow is the hot water while the purple part is the cold water which is been added to the cold water. Because the cold water is just about to be mixed with the very hot water, that is why the two could show it temperature before finally mixing up.

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When you sit down somewhere at the corner of your living room, you press your remote control to change channels from a news channel to a football channel or a science discovery Channel. With the remote, you saves time from going to your Television, turning the knob to change the channel or it's on/off mode or whatever function you want the Television to perform for you

The remote function effectively because it contain an Infrared Light- Emitting Diode which transmit sequence of electrical rhythm that constitutes numbers, characters with operations to be performed. The television contains a detector which then converts light impulse from the remote control to
electrical signals that gives commands to a microprocessor on the board inside the television. The command received by the microprocessor then change the channel, modify the volume as the case may be.

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Conclusion.

Human eyes is only limited to see objects as long as it emitts heat within the visible region of the electromagnetic spectrum. The whole of the electromagnetic spectrum are at different energy, frequency and wavelength and Infra-Red is one of spectrum. Infra-Red which is just below red edge of visible spectrum (Infra means below) has a long wavelength compared with the visible light, has short frequency and energy. It's is widely applied in different aspects of sciences for imaging purpose and for sophisticated security system which would be difficult for Intruders to break through.[The introduction, laser security system]

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REFERENCES

Tutorials/em-spectrum

Our_Activities/Space_Science

Wikipedia.org/wiki/Astronomy

Wikipedia.org/wiki/Infrared

nasa.gov/science/toolbox/emspectrum

Image_galleries/ir_zoo/lessons/background

How-do-night-vision-goggles-work

Laser-security-system-protect-your-home-like-a-top-secret-government-facility