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LASER (Light Amplification by the Stimulated Emission of Radiation)
In 1917 a process called Stimulated Emission, this is what makes lasers possible and was thought of by Albert Einstein. Although this was thought of so early, it took another 30 years before other physicists made practical usage of this principle. Once completed, scientists were amazed at the breakthrough, however it didn’t, at the time, have any real use.

Lasers is a source of light used in our everyday lives. They are very focused and accurate sources of light, thus we find them almost anywhere and help us in many different ways.

They are incredibly useful in the Medical Field. They are often used in Laser Eye Surgery and Laser Ulcer Removal.
They do so, because the laser beam is so intense, it burns through a tiny amount of tissue within the eye. The laser can also be used as a scalpel, which can make a small incision to reach the stomach ulcer.

Lasers are also used in Compact Disk Players, CDs/DVDs/Blu Ray, Super Market Scanners, Laser Shows, Fiber Optic Cables, Cutting, Measuring Distance and much more. Clearly lasers have a major impact in our lives as advancing human beings.

Atoms can get “excited” when they take in light, heat and/or electricity. Usually though atoms will remain in a “ground state” which is more stable, and will return to this state within nanoseconds. However to return to this state, the atoms must relieve themselves of the current energy, the energy is rid of equally to the difference between the two levels of energy (ΔE = E2 – E1) and then becomes a photon, this is ultimately spontaneous emission.
For lasers to be successful, a form called popular inversion must be met. This happens when a number of excited atoms within a system, is greater than atoms in a grounded state.
Lasers are basically made up of photons, the basic unit of light. Photons are always moving, and moving at a constant speed of c = 2.998 x 10^8 (the speed of light)
A basic laser only needs 3 sections to work, pump source, gain medium and optical resonator.
Pump source is energy that is supplied to the laser
A gain medium is a supply of atoms needed to reach stimulated emission and population inversion. This is huge factor, which will result in the laser’s wavelength, its colour and a number of other properties.
Many, many different gain mediums have been used in 1960, laser discovered and first used, to see if they ever would be discovered. Thousands of gain mediums have been trailed to form in a positive result for lasers debut, such gain mediums include methanol, crystal, glass, argon, carbon dioxide, semiconductors and even jello has been used.
An optical resonator is simply, two mirrors parallel to each other at opposite ends, in between the gain medium.
The pump sauce starts, photons are made and are scattered, then emitted in numerous directions.
Types of Laser include:
Solid-State Lasers
The most common solid laser media are rods of ruby crystals and neodymium-doped glasses and crystals. The ends of the rod are fashioned into two parallel surfaces coated with a highly reflecting non-metallic film. Solid-state lasers offer the highest power output. They are usually operated in a pulsed manner to generate a burst of light over a short time. Bursts as short as 12 × 10-15 sec have been achieved, which are useful in studying physical phenomena of very brief duration. Pumping is achieved with light from xenon flash tubes, arc lamps, or metal-vapour lamps. The frequency range has been expanded from infrared (IR) to ultraviolet (UV) by multiplying the original laser frequency with crystal-like potassium dihydrogen phosphate, which are even shorter, and X-ray wavelengths, which are even shorter, have been achieved by aiming laser beams at yttrium targets.

Gas Lasers
The laser medium of a gas laser can be a pure gas, a mixture of gases, or even metal vapour, and is usually contained in a cylindrical glass or quartz tube. Two mirrors are located outside the ends of the tube to form the laser cavity. Gas lasers are pumped by ultraviolet light, electron beams, electric current, or chemical reactions. The helium-neon laser is known for its high frequency stability, colour purity, and minimal beam spread. Carbon dioxide lasers are very efficient, and consequently they are the most powerful continuous wave (CW) lasers.

Semiconductor Lasers
The most compact of lasers, the semiconductor laser usually consists of a junction between layers of semiconductors with different electrical conducting properties. The laser cavity is confined to the junction region by means of two reflective boundaries. Gallium arsenide is the semiconductor most commonly used. Semiconductor lasers are pumped by the direct application of electrical current across the junction, and they can be operated in the CW mode with better than 50 per cent efficiency. A method that permits even more efficient use of energy has been devised. It involves mounting tiny lasers vertically in such circuits, to a density of more than a million per square centimetre. Common uses for semiconductor lasers include CD players (see Sound Recording and Reproduction) and laser printers.