Infrared Waves

Infrared waves have very short wavelengths, which are longer than the visible light at 0.74 micrometers, and extending conventionally to 300 micrometers. These wavelengths correspond to a frequency range of approximately 1 to 400 THz.

7 bands of Infrared Radiation

The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy.

There are three bands of Infrared radiation as stipulated by the International Commission on Illumination (CIE) as follows:

  • IR-A: 700 nm–1400 nm (0.7 µm – 1.4 µm, 215 THz – 430 THz)
  • IR-B: 1400 nm–3000 nm (1.4 µm – 3 µm, 100 THz – 215 THz)
  • IR-C: 3000 nm–1 mm (3 µm – 1000 µm, 300 GHz – 100 THz)

However, the ISO 20473 standard divides the Infrared as follows:

The Infrared radiation can also be divided into 7 bands for the purpose of Telecommunication as follows:

7 bands of Infrared Radiation

BandDescriptorWavelength range
O bandOriginal1260–1360 nm
E bandExtended1360–1460 nm
S bandShort wavelength1460–1530 nm
C bandConventional1530–1565 nm
L bandLong wavelength1565–1625 nm
U bandUltralong wavelength1625–1675 nm

Applications of Infrared

Infra-red waves have wide ranging uses as follows discussed below

Active-infrared night vision

In this, the camera illuminates the scene at infrared wavelengths invisible to the human eye.  Infrared is used in night vision equipment when there is insufficient visible light to see.

How the Night vision devices work?

Night vision goggles work on the principle of infrared radiation, which radiates from any object  in relation to its temperature. A hotter body radiates more infrared radiation. A night vision goggle receives this radiation from the surroundings and makes out places which are comparatively warmer (usually warm-blooded animals like human beings) helping the user to see in the dark or through a fog. Please note that night vision devices operate through a process involving the conversion of ambient light photons into electrons which are then amplified by a chemical and electrical process and then converted back into visible light.

What is difference between night vision and thermal imaging?

Both vision and thermal imaging work on the basis of properties of the infrared radiation but the working is different. Thermal imaging creates images based on differences in surface temperature by detecting infrared radiation (heat) that emanates from objects and their surrounding environment. Thermographic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 900–14,000 nanometers or 0.9–14 μm) and produce images of that radiation.

Thermography & Pyrometry

Infrared radiation can be used to remotely determine the temperature of objects. If they are used in case of very hot objects, it is called thermography, while if used in visible, then it is termed pyrometry. Thermography  is mainly used in military and industrial applications but the technology is reaching the public  in the form of infrared cameras on cars.

Hyperspectral imaging

Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. Much as the human eye sees visible light in three bands (red, green, and blue), spectral imaging divides the spectrum into many more bands.  Hyperspectral imaging is gaining importance in the applied spectroscopy. Its applications include biological, mineralogical, defence, and industrial measurements.

Infrared tracking

Infrared tracking, also known as infrared homing, refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it.

What are Heat seekers?

Missiles which use infrared seeking are often referred to as “heat-seekers”, since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines, and aircraft generate and retain heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background.

Communications

IR data transmission is used in short-range communication among computer peripherals and personal digital assistants.  The standards to use these devices are published by IrDA (Infrared Data Association).

How Remote Controls work?

The devices such as Remote Controls use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for remote controls to command appliances. Infrared remote control protocols like RC-5, SIRC, are used to communicate with infrared.

Spectroscopy

Infrared vibrational spectroscopy is a technique which can be used to identify molecules by analysis of their constituent bonds.

Meteorology

The Weather satellites equipped with scanning radiometers produce thermal or infrared images which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features. The scanning is typically in the range 10.3-12.5 µm (IR4 and IR5 channels). Satellites use sensors whose working principle is based on photoelectric effect, converting radiation reaching the sensor into electric charge, which can then be easily measured and processed.

Essentially, the energy detected over a given spectral band, whether it is in the Thermal / Infrared (or even microwave) band, is converted to an array of digits corresponding to the energy range and radioed to ground stations. After receiving it, those digital values corresponding to the measured energy range (known as grey levels) are finally printed on a computer screen as a picture or as a conventional photograph. The main advantage of infrared is that images can be produced at night, allowing a continuous sequence of weather to be studied.

Climatology

Infrared pictures can depict ocean eddies or vortices and map currents such as the Gulf Stream, even El Niño phenomena can be spotted.  Infrared can detect trends in the energy exchange between the earth and the atmosphere. These trends provide information on long term changes in the Earth’s climate. It is one of the primary parameters studied in research into global warming together with solar radiation.

Astronomy

Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of optical astronomy. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium. However, sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected atmospheric windows. It can be partially alleviated by placing the telescope observatory at a high altitude, or by carrying the telescope aloft with a balloon or an aircraft. Space telescopes do not suffer from this handicap, and so outer space is considered the ideal location for infrared astronomy. The Spitzer Space Telescope is a dedicated infrared space observatory currently in orbit around the Sun.

Historical Studies

Use of infrared are made by historians on various types of objects, especially very old written documents such as the Dead Sea Scrolls, the Roman works in the Villa of the Papyri, and the Silk Road texts found in the Dunhuang Caves. Carbon black used in ink can show up extremely well.

Biology

The pit viper has a pair of infrared sensory pits on its head, however not much details are known about its functionality. The other organisms that have thermo receptive organs are pythons, some boas , the Common Vampire Bat, some beetles, some darkly pigmented butterflies.

Photobiomodulation

It’s a chemotherapy induced oral ulceration as well as wound healing that uses near infrared light.

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