Wavelengths in the context of Microwave engineering

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state. The photon energy of the emitted photons is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.

False colors and pseudo colors respectively refers to a group of color rendering methods used to display images in colors which were recorded in the visible or non-visible parts of the electromagnetic spectrum. A false-color image is an image that depicts an object in colors that differ from those a photograph (a true-color image) would show. In this image, colors have been assigned to three different wavelengths that human eyes cannot normally see.

In addition, variants of false colors such as pseudocolors, density slicing, and choropleths are used for information visualization of either data gathered by a single grayscale channel or data not depicting parts of the electromagnetic spectrum (e.g. elevation in relief maps or tissue types in magnetic resonance imaging).

Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorophyll does not reflect light but chlorophyll-containing tissues appear green because green light is diffusively reflected by structures like cell walls. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain. Chlorophyll a also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located.

Infrared homing is a passive weapon guidance system which uses the infrared (IR) light emission from a target to track and follow it seamlessly. Missiles which use infrared seeking are often referred to as "heatseekers" since infrared is radiated strongly by hot bodies. Many objects such as people, vehicle engines and aircraft generate and emit heat and so are especially visible in the infrared wavelengths of light compared to objects in the background.

Infrared seekers are passive devices, which, unlike radar, provide no indication that they are tracking a target. That makes them suitable for sneak attacks during visual encounters or over longer ranges when they are used with a forward looking infrared or similar cueing system. Heat-seekers are extremely effective: 90% of all United States air combat losses between 1984 and 2009 were caused by infrared-homing missiles. They are, however, subject to a number of simple countermeasures, most notably by dropping flares behind the target to provide false heat sources. That works only if the pilot is aware of the missile and deploys the countermeasures on time. The sophistication of modern seekers has rendered these countermeasures increasingly ineffective.

Solar gain (also known as solar heat gain or passive solar gain) is the increase in thermal energy of a space, object or structure as it absorbs incident solar radiation. The amount of solar gain a space experiences is a function of the total incident solar irradiance and of the ability of any intervening material to transmit or resist the radiation.

Objects struck by sunlight absorb its visible and short-wave infrared components, increase in temperature, and then re-radiate that heat at longer infrared wavelengths. Though transparent building materials such as glass allow visible light to pass through almost unimpeded, once that light is converted to long-wave infrared radiation by materials indoors, it is unable to escape back through the window since glass is opaque to those longer wavelengths. The trapped heat thus causes solar gain via a phenomenon known as the greenhouse effect. In buildings, excessive solar gain can lead to overheating within a space, but it can also be used as a passive heating strategy when heat is desired.

The Infrared Space Observatory (ISO) was a space telescope for infrared light designed and operated by the European Space Agency (ESA), in cooperation with ISAS (now part of JAXA) and NASA. The ISO was designed to study infrared light at wavelengths of 2.5 to 240 micrometres and operated from 1995 to 1998.

The €480.1-million satellite was launched on 17 November 1995 from the ELA-2 launch pad at the Guiana Space Centre near Kourou in French Guiana. The launch vehicle, an Ariane 44P rocket, placed ISO successfully into a highly elliptical geocentric orbit, completing one revolution around the Earth every 24 hours. The primary mirror of its Ritchey-Chrétien telescope measured 60 cm in diameter and was cooled to 1.7 kelvins by means of superfluid helium. The ISO satellite contained four instruments that allowed for imaging and photometry from 2.5 to 240 micrometres and spectroscopy from 2.5 to 196.8 micrometers.

A metamaterial (from the Greek word μετά meta, meaning 'beyond' or 'after', and the Latin word materia, meaning 'matter' or 'material') is an engineered material whose properties arise not from the chemical composition of its base substances, but from their deliberately designed internal structure. These properties are often rare or absent in naturally occurring materials. Metamaterials are typically fashioned from multiple materials, such as metals and plastics, and arranged in repeating patterns at scales that are smaller than the wavelengths of the phenomena they influence. Their shape, geometry, size, orientation, and arrangement give them their properties of manipulating electromagnetic, acoustic, or seismic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials. Those that exhibit a negative index of refraction for particular wavelengths have been the focus of a substantial amount of research.

Potential applications of metamaterials are diverse and include sports equipment, optical filters, medical devices, remote aerospace applications, sensor detection and infrastructure monitoring, smart solar power management, lasers, crowd control, radomes, high-frequency battlefield communication and lenses for high-gain antennas, improving ultrasonic sensors, and even shielding structures from earthquakes. Metamaterials offer the potential to create super-lenses. A form of 'invisibility' was demonstrated using gradient-index materials. Acoustic and seismic metamaterials are also research areas.

Luminous infrared galaxies or LIRGs are galaxies with luminosities above 10 L_☉. They are also referred to as submillimeter galaxies (SMGs) through their normal method of detection. LIRGs are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. A LIRG's luminosity is 100 billion times that of the Sun.

Galaxies with luminosities above 10 L_☉ are known as ultraluminous infrared galaxies (ULIRGs). Galaxies exceeding 10 L_☉ are characterised as hyper-luminous infrared galaxies (HyLIRGs). Those exceeding 10 L_☉ are extremely luminous infrared galaxies (ELIRGs). Many of the LIRGs and ULIRGs are showing interactions and disruptions. Many of these types of galaxies spawn about 100 new stars a year as compared to the Milky Way which spawns one a year; this helps create the high level of luminosity.