LASER

Types of Lasers

Common types of lasers are:

Semiconductor lasers (mostly laser diodes), electrically (or sometimes optically) pumped, efficiently generating very high output powers (but typically with poor beam quality), or low powers with good spatial properties (e.g. for application in CD and DVD players), or pulses (e.g. for telecom applications) with very high pulse repetition rates. Special types include quantum cascade lasers (for mid-infrared light) and surface-emitting semiconductor lasers (VCSELs and VECSELs), the latter also being suitable for pulse generation with high powers.

Solid-state lasers based on ion-doped crystals or glasses (doped insulator lasers), pumped with discharge lamps or laser diodes, generating high output powers, or lower powers with very high beam quality, spectral purity and/or stability (e.g. for measurement purposes), or ultrashort pulses with picosecond or femtosecond durations. Common gain media are Nd:YAG, Nd:YVO4, Nd:YLF, Nd:glass, Yb:YAG, Yb:glass, Ti:sapphire, Cr:YAG and Cr:LiSAF.

A special type of ion-doped glass lasers are:

Fiber lasers, based on optical glass fibers which are doped with some laser-active ions in the fiber core. Fiber lasers can achieve extremely high output powers (up to kilowatts) with high beam quality, allow for widely wavelength-tunable operation, narrow linewidth operation, etc.

Gas lasers (e.g. helium–neon lasers, CO2 lasers, and argon ion lasers) and excimer lasers, based on gases which are typically excited with electrical discharges. Frequently used gases include CO2, argon, krypton, and gas mixtures such as helium–neon. Common excimers are ArF, KrF, XeF, and F2.

Less common are chemical and nuclear pumped lasers, free electron lasers, and X-ray lasers.

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Helium Neon Lasers

Helium–neon (He–Ne) lasers are a frequently used type of continuously operating gas lasers, ' most often emitting red light at 632.8 nm at a power level of a few milliwatts and with excellent beam quality. The gain medium is a mixture of helium and neon gas in a glass tube, which normally has a length of the order of 15–50 cm.

In the gas discharge, helium atoms are excited into a metastable state. During collisions, the helium atoms can efficiently transfer energy to neon atoms, which have an excited state with similar excitation energy. Neon atoms have a number of energy levels below that pump level, so that there are several possible laser transitions. The transition at 632.8 nm is the most common, but other transitions allow the operation of such lasers at 1.15 μm, 543.5 nm (green), 594 nm (yellow), 612 nm (orange), or 3.39 μm. The emission wavelength is selected by using resonator mirrors which introduce high enough losses at the wavelengths of all competing transitions.















































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Ruby Laser

Ruby is an aluminum oxide crystal in which some of the aluminum atoms have been replaced with chromium atoms. Chromium gives ruby its characteristic red color and is responsible for the lasing behavior of the crystal. Chromium atoms absorb green and blue light and emit or reflect only red light. For a ruby laser, a crystal of ruby is formed into a cylinder. A fully reflecting mirror is placed on one end and a partially reflecting mirror on the other. A high-intensity lamp is spiraled around the ruby cylinder to provide a flash of white light that triggers the laser action. The green and blue wavelengths in the flash excite electrons in the chromium atoms to a higher energy level. Upon returning to their normal state, the electrons emit their characteristic ruby-red light. The mirrors reflect some of this light back and forth inside the ruby crystal, stimulating other excited chromium atoms to produce more red light, until the light pulse builds up to high power and drains the energy stored in the crystal.

The optically pumped, solid-state laser uses sapphire as the host lattice and chromium as the active ion. The emission takes place in the red portion of the spectrum.

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