Dr. Noor Al-Huda Al-Aaraji Third Stage

Laser Definition can be defined as a device that activates electrons to emit electromagnetic radiation. This laser definition means radiation can take the form of any kind on the electromagnetic spectrum, from radio waves to gamma rays.

The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation."

A laser differs from other sources of light in that it emits light which is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as . Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i.e., they can emit a single color of light .

Lasers are used in optical disk drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic, semiconducting chip manufacturing (photolithography), and free-space optical communication, and skin treatments, cutting and welding materials, enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. They have been used for car headlamps on luxury cars, by using a laser and a phosphor to produce There are many types of lasers available for research, medical, industrial, and commercial uses. Lasers are often described by the kind of lasing medium they use - solid state, gas, excimer, dye, or semiconductor.

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Dr. Noor Al-Huda Al-Aaraji Third Stage Laser

Spontaneous emission

If a light source ('the atom') is in an excited state with energy E2 it may spontaneously decay to a lower lying level (e.g., the ground state) with energy E2 , releasing the difference in energy between the two states as a photon. The photon will have angular frequency w and an energy h w

E2-E1=h w

Note: (h w=h v) where h is the Planck constant and v is the linear frequency. The phase of the photon in spontaneous emission is random as is the direction in which the photon propagates. This is not true for stimulated emission. An energy level diagram illustrating the process of spontaneous emission is shown below:

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Dr. Noor Al-Huda Al-Aaraji Third Stage Laser

Stimulated Emission

When an electron is excited from a lower to a higher energy level, it's unlikely for it to stay that way forever. An electron in an excited state may decay to a lower energy state which is not occupied, according to a particular time constant characterizing that transition. When such an electron decays without external influence, emitting a photon, that is called "spontaneous emission". the rate of transitions between two stationary states is increased beyond that of spontaneous emission. A transition from the higher to a lower energy state produces an additional photon with the same phase and direction as the incident photon; this is the process of stimulated emission.

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Dr. Noor Al-Huda Al-Aaraji Third Stage Laser

Properties of laser 1-Monochromatic The light emitted from a laser is monochromatic, that is, it is of one (color). In contrast, ordinary white light is a combination of many different (colors).

2-Directional Lasers emit light that is highly directional. Laser light is emitted as a relatively narrow beam in a specific direction. Ordinary light, such as coming from the sun, a light bulb, or a candle, is emitted in many directions away from the source.

3-Coherent The light from a laser is said to be coherent, which means the wavelengths of the laser light are in phase in space and time.

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Dr. Noor Al-Huda Al-Aaraji Third Stage Laser

Types of Lasers

1- Solid state lasers have lasing material distributed in a solid matrix, e.g., the ruby or neodymium-YAG (yttrium aluminum garnet) lasers. The neodymium-YAG laser emits light at 1.064 micrometers.

2- Gas lasers (helium and helium-neon, HeNe, are the most common gas lasers) have a primary output of a visible red light. CO2 lasers emit energy in the far-infrared, 10.6 micrometers, and are used for cutting hard materials.

3- Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases such as chlorine and fluorine mixed with inert gases such as argon, krypton, or xenon. When electrically stimulated, a pseudomolecule or dimer is produced and when lased, produces light in the range.

4- Dye lasers use complex organic dyes like rhodamine 6G in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.

5- Semiconductor lasers, sometimes called diode lasers, are not solid- state lasers. These electronic devices are generally very small and use low

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Dr. Noor Al-Huda Al-Aaraji Third Stage Laser

power. They may be built into larger arrays, e.g., the writing source in some laser printers or compact disk players. highly directional white light.

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