Functioning like a laser, high concentration of a beaming maser has the ability to knock out all electronics, which is needed for the functioning in all equipments, rendering equipments useless.
– Contributed by Oogle.
An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum.
Like a laser, the emission from a maser is stimulated (or seeded) and monochromatic, having the frequency corresponding to the energy difference between two quantum-mechanical energy levels of the species in the gain medium which have been pumped into a non-thermal population distribution. However, naturally occurring masers lack the resonant cavity engineered for terrestrial laboratory masers. Indeed, the emission from an astrophysical maser is due to a single pass through the gain medium and therefore generally lacks the spatial coherence and mode purity expected of laboratory instruments.
Furthermore, the practical limits of the use of the m to stand for microwave in maser are variously employed. For example, when lasers were initially developed in the visible portion of the spectrum they were called optical masers. Townes advocated that the m stand for molecule since energy states of molecules generally provide the masing transition. Along these lines, some will use the term laser to describe any system which exploits an electronic transition and the term maser to describe a system which exploits a rotational or vibrational transition, regardless of the output frequency. Some astrophysicists use the term iraser to describe a maser emitting at a wavelength of a few micrometres, even though the optics community has similar sources which they call lasers. The term taser has been used to describe laboratory masers in the terahertz regime although astronomers might call these sub-millimeter masers and laboratory physicists generally call these gas lasers or specifically alcohol lasers in reference to the gain species. The electrical engineering community typically limits the use of the word microwave for frequencies roughly between 1 GHz and 300 GHz.
Characteristics of Maser Radiation
The amplification or gain of radiation passing through a maser cloud is exponential. This has consequences for the radiation they produce:
Small path differences across the irregularly shaped maser cloud become greatly distorted by exponential gain. Part of the cloud that has a slightly longer path length than the rest will appear much brighter (as it is the exponent of the path length that is relevant), and so maser spots are typically much smaller than their parent clouds. The majority of the radiation will emerge along this line of greatest path length in a “beam”; this is termed beaming.
As the gain of a maser depends exponentially on the population inversion and the velocity-coherent path length, any variation of either will itself result in exponential change of the maser output.
Exponential gain also amplifies the centre of the line shape (Gaussian or Lorentzian, etc.) more than the edges or wings. This results in an emission line shape that is much taller but not much wider. This makes the line appear narrower relative to the unamplified line.
The exponential growth in intensity of radiation passing through a maser cloud continues as long as pumping processes can maintain the population inversion against the growing losses by stimulated emission. While this is so the maser is said to be unsaturated. However, after a point, the population inversion cannot be maintained any longer and the maser becomes saturated. In a saturated maser, amplification of radiation depends linearly on the size of population inversion and the path length. Saturation of one transition in a maser can affect the degree of inversion in other transitions in the same maser, an effect known as competitive gain.
The brightness temperature of a maser is the temperature a black body would have if producing the same emission brightness at the wavelength of the maser. That is, if an object had a temperature of about 109K it would produce as much 1665-MHz radiation as a strong interstellar OH maser. Of course, at 109K the OH molecule would dissociate (kT is greater than the bond energy), so the brightness temperature is not directly indicative of the kinetic temperature of the maser gas but is nevertheless useful in describing maser emission. Masers have huge effective temperatures, many around 109K, but some of up to 1012K and even 1014K.
An important aspect of maser study is polarisation of the emission. Astronomical masers are often very highly polarised, sometimes 100% (in the case of some OH masers) in a circular fashion, and to a lesser degree in a linear fashion. This polarisation is due to some combination of the Zeeman effect, magnetic beaming of the maser radiation, and anisotropic pumping which favours certain magnetic-state transitions.
It should be noted that many of the characteristics of megamaser emission are different.
(Reuters) – The U.S. Navy F/A-18 jet fighter suffered what a Pentagon official described as “a catastrophic mechanical malfunction” during a training flight before it crashed shortly after take-off. Both crew members ejected and one was found still strapped into his ejection seat.
Thick black clouds of smoke billowed into the air as fire reduced the apartment buildings to a blackened shell. The Mayfair Mews complex was less than two miles from Naval Air Station Oceana, where the F-18 was based.
Navy officials said a thorough investigation into the crash could take several weeks. They have not yet listened to the flight recorders onboard the plane, they said.
(Reporting by Anna Yukhananov; Editing by Sandra Maler and Philip Barbara)