Maser, principle of operation, types of masers.
Maser – quantum generator, emitting coherent electromagnetic waves in the centimeter range (microwaves).
Maser (eng. maser) – quantum generator, emitting coherent electromagnetic waves in the centimeter range (microwaves).
Maser is the acronym for the device formed by the first letters of each word of the phrase “Microwave Amplification by Stimulated Emission of Radiation”, which translated to English means “Amplification of microwaves using stimulated emission“.
The principle of its action maser similar to a laser, but it works in the microwave range.
In standard conditions the atoms and molecules of a substance are in thermodynamic equilibrium with each other and with the environment. Thus, the higher the energy of the excited state of an atom or molecule, the smaller the number of atoms and moleculesbeing in the excited state. To create a stimulated emission of the atoms and molecules of a substance, it must be placed in a non-equilibrium environment in which the number of excited atoms or molecules more than unexcited. Excited atoms or molecules have electrons in higher energy levels. In the transition from the excited state (level), i.e. with a higher energy level to a lower level, i.e., normal, stable, unexcited state of an atom or molecule emits a photon – a quantum of electromagnetic radiation. However, in some cases there is a spontaneous emission, and in others forced. When the stimulated emission resulting electromagnetic wave propagates in the same direction as the original inducing wave, frequency and polarization of the stimulated radiation and the original equal, a forced flow of coherent exciting.
Historically, the first was created by the masers. Their creation ushered in an era of quantum electronics. Subsequently, the principles of operation of masers was created and quantum generators of light — lasers.
The type of active medium, in which there are quantum amplification and generation of electromagnetic waves, masers are divided into two types:
molecular oscillators – masers using molecular beams. In this type of maser active medium is created by an artificial sort of beam of molecules of a substance only those molecules that are in excited state. The sorted beam of molecules in the excited state, falls into a resonant cavity, where there is an accumulation of the excited molecules. In a resonator excited molecules in the transition to a normal, stable, non-excited state emit a quantum of electromagnetic radiation in the centimeter range, which transfer to the field of the resonator. The resonator is configured so that the resonant frequency of the resonator equal to the frequency of electromagnetic radiation emitted by the excited molecule during the transition to the ground state. Therefore, such a resonator is able longer time to maintain electromagnetic oscillations, excited in the resonator at the resonance frequency.
Among the molecular oscillators are masers operating on ammonia and hydrogen. The wavelength of the ammonia maser is 1.27 cm, the hydrogen maser – 21 see Their primary use as standards of time and frequency;
– paramagnetic oscillators and amplifiers – masers, using as an active medium of paramagnetic crystals. The active medium in these masers is a paramagnetic crystal (e.g. ruby crystal) which is placed in the cavity. Unlike the cavity in the molecular oscillator, the resonator paramagnetic oscillator has two resonant frequencies: the frequency of the pump radiation and the frequency gain. The transition of the molecules of the crystal in the excited state occur by absorption of a crystal the electromagnetic radiation of a pumping wavelength less than the wavelength of the gain and the gain of the excited state by putting the crystal together with the resonator in a constant magnetic field, adjustment of which can change the energy level of the excited molecules or atoms. At the transition of the excited molecules of a substance in a normal, stable, unexcited state, they emit a quantum of electromagnetic radiation in the centimeter range, which is misleading field of the resonator.
Paramagnetic oscillators and amplifiers capable of generating wavelengths from 1 to 100 cm.
The most important property of paramagnetic generators and amplifiers – very low noise level 100 times lower than in the amplifiersoperating on different principles. Therefore, paramagnetic oscillators and amplifiers have found their use in radio astronomy and radar systems to amplify weak radio signals.
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