Properties of Laser There are Severel Properties Of LASER which are defined as follows:- MONOCHROMATICITY COHERENCE DIRECTIONALITY BRIGHTNESS DIVERGENCE INTENSITY These are several Properties about LASER which we will be going to discuss in this Presentation.

MONOCHROMATICITY:- The energy of a photon determines its wavelength through the relationship E = hc/λ, where c is the speed of light, h is Planck's constant, and λ is wavelength. In an ideal case, the laser emits all photons with the same energy, and thus the same wavelength, it is said to be monochromatic. The light from a laser typically comes from one atomic transition with a single precise wavelength. So the laser light has a single spectral color and is almost the purest monochromatic light available. 

COHERENCE When an excited atom, depending on its lifetime at the higher energy level, comes down to lower energy level, a photon is emitted, corresponding to the equation, hv = E2 - E1 where h is the Planks constant, n is the frequency of the emitted photon and E2 and E1 correspond to higher and lower energy levels respectively. This type of natural emission occurs in different directions and is called spontaneous emissions. It is characterized by the lifetime of the upper excited state after which it spontaneously returns to lower state and radiates away the energy by emission. 

Directionality One of the important properties of laser is its high directionality. The mirrors placed at opposite ends of a laser cavity enables the beam to travel back and forth in order to gain intensity by the stimulated emission of more photons at the same wavelength, which results in increased amplification due to the longer path length through the medium. The multiple reflections also produce a well-collimated beam, because only photons traveling parallel to the cavity walls will be reflected from both mirrors. If the light is the slightest bit off axis, it will be lost from the beam.

BRIGHTNESS It is defined as the power emitted per unit surface area per unit solid angle. The units are watts per square meter per steradian. A steradian is the unit of solid angle, which is three-dimensional analogue of conventional two-dimensional (planar) angle expressed in radians. For small angles the relation between a planar angle and the solid angle of a cone with that planar angle is to a good approximation is: Ω = (π / 4) θ2 where θ is the planar angle and Ω is the solid angle as shown in the figure.

TYPES OF LASER Solid Laser Gas Laser Liquid(Dye) Laser Semiconductor Laser

SOLID-STATE LASER A solid-state laser is a laserthat uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers.For eg. Ruby Lasers,Nd-YAG,etc

GAS LASERS A gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate on the principle of converting electrical energy to a laser light output. The first gas laser, the Helium–neon laser (HeNe), was co-invented by Iranian-American physicist Ali Javan and American physicist William R. Bennett, Jr. in 1960. It produced a coherent light beam in the infrared region of the spectrum at 1.15 micrometres.

DYE LASER A dye laser is a laser which uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 nanometers or more. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. The dye rhodamine 6G, for example, can be tuned from 635 nm (orangish-red) to 560 nm (greenish-yellow), and produce pulses as short as 16 femtoseconds. 

Semiconductor Lasers Semiconductor lasers or laser diodes play an important part in our everyday lives by providing cheap and compact-size lasers. They consist of complex multi-layer structures requiring nanometer scale accuracy and an elaborate design. Their theoretical description is important not only from a fundamental point of view, but also in order to generate new and improved designs. It is common to all systems that the laser is an inverted carrier density system. The carrier inversion results in an electromagnetic polarization which drives an electric field E(t). In most cases, the electric field is confined in a resonator, the properties of which are also important factors for laser performance. Semiconductor Lasers(520nm,445nm,635nm)

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