MASER

A journey through an acronym

begin

MASER’s

MicrowaveAmplification by the

StimulatedEmission of

Radiation

Masers in Space

Microwave

Masers are just like lasers except that the radiation they emit is in the microwave part of the electromagnetic spectrum (learn more). This light has a longer wavelength and less energy than the visual light emitted by lasers. Masers were created in the laboratory in the 1950’s, before the invention of the Laser.

Amplified

Radiation from a maser or laser is much more intense than radiation from other light sources. The amplified light from lasers can be strong enough to cut through granite (learn more). The amplified light from Masers can be strong enough to be seen from billions of light years away. To radio telescopes, masers look like very small, very bright dots. Just as if someone was shining a laser-pointer at you from across the room.

Stimulated Emission

• Masers are so powerful because they emit from regions with a population inversion.

• These regions are unstable and can lead to the stimulated emission of large quantities of radiation.

Population Inversion

Every electron in a system has a certain amount of energy. In most systems, the number of low energy electrons outnumber those with high energy. Population Inversion occurs when most of the electrons are in the higher energy state.

Normal population Inverted population

more Population Inversion

There are several ways in which a system can be “pumped” into this higher energy state including . . .

• Collisions with other particles

• Absorbing light

• Being placed in an electric field

Stimulated EmissionIn the inverted population, one of the electrons randomly jumps to the lower energy level. When it does, it emits a photon with an energy equal to the energy difference between the two levels. As this photon passes another electron, its mere presence stimulates the release of another photon. Because their release was stimulated, the group of photons has unique properties.

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Radiation

Light bulbs emit electromagnetic radiation in a most disorganized way. MASERS emit radiation much more orderly. Because they were produced by stimulated emission, all the photons are monochromatic, in phase, similarly polarized, and travel in the same direction.

Monochromatic

Light is a wave with frequency, wavelength and energy. All three are related. The “light” emitted by a MASER is of one frequency, wavelength and energy. Color is related to frequency and so the light is said to be monochromatic. (Mono = one, chromatic = color)

monochromatic not monochromatic

In phase

• Light is a wave and has a wavelength.

• If two waves begin at the same point, they are in phase. Added together, their amplitude increases.

• When two waves begin at different points, they are out of phase. If they are added together, their amplitude decreases.

Polarization

Waves can be polarized in four different ways. All the microwaves emitted by a maser are polarized in the same way. (learn more)

Right handed

left handed

Vertical

Horizontal

Masers in Space

Several different types of molecular masers have been discovered in space. They produce radiation using chemicals including:

Hydroxyl (OH) Formaldehyde (H2CO) Ammonia (NH3) Hydrogen Cyanide (HCN)

Water (H2O) Silicon Monoxide (SiO) Methanol (CH3OH)

Each maser produces radiation at a characteristic frequency.

Because these sources are so strong, astrochemists use them to find and identify

new chemicals in space.

Where are they?

Many of these masers are found in planetary nebulae – the clouds of gas around red giant stars (learn more). Light from the star pumps the gas into its population inversion state.

This planetary nebula has three different names: M 2-9, Siamese Squid Nebula, and Twinjet Nebula

Let’s all get togetherIn order for stimulated emission to occur, the gas particles must all be close together, moving in the same direction, and moving at the same speed. Masers often occur in a shell that forms as shock waves ripple through space around mature stars.

Masers reveal the characteristics of their environment.

• They can be used as probes to determine the density, temperature, pressure, and velocity of a region of space.

• Masers were used in the first proof of the existence a black hole!

• Masers were found circling a massive object. They circled very fast, indicating that the object had to be very dense. Mathematics showed that an object so dense could not be anything but a black hole.

• (learn more ) (learn more)