The document summarizes the history and science behind lasers. It discusses how the laser was first conceived in the 1950s and built in 1960. It then explains the basic components of a laser including an energy input source and a gain medium that produces stimulated emission when pumped with energy. Examples of common laser types and materials are provided. Applications of lasers in spectroscopy, surgery, and distance measurements to the moon are also mentioned.

1. LASER & ITS APPLICATIONPRESENTED BY :-TUHIN DAS

2. WELDING & CUTTING OF METAL

3. THE DISCOVERY OF THE LASERThe maser which was the predecessor of the laser and emitted microwaves was first built in 1953. Some of the first work done on the laser was started in 1957 by Charles Hard Townes and Arthur Leonard ' at Bell Labs. Their original work was with infrared frequencies but they later changed their focus to visible light and the optical maser which was how the laser was first referred to. Working independently of Townes and Schawlow and of each other were Gordon Gould a graduate student at Columbia University and Aleksandr Mikhailovich Prokhorov. All parties had the idea of using an open resonator which became an important part of the laser. In 1959 Gould applied to the US patent office for a patent for the laser but he was refused and the patent instead went to Bell Laboratories in 1960. The first working laser was built by Theodor Harold Maiman working at Hughes Research Laboratories in Malibu California.

4. FORMATION OF LASER

5. A laser basically consists of two main parts, an energy input and a gain medium. The energy input is called a pump source, in the above example it is a flash lamp but the pump source could also be an electrical power supply, a chemical reaction or another laser. The power source inputs energy which is called laser pumping energy, this is what drives the process which produces the laser light. The pumping energy is directed into the gain medium, this is the material which gives different lasers their individual characteristics. There are many different materials used as gain media including crystalline solids usually doped with transition metal ions or rare earth ions, gases such as CO2 or. He, semiconductors such as gallium arsenide and liquids dyes.A laser basically consists of two main parts, an energy input and a gain medium. The energy input is called a pump source, in the above example it is a flash lamp but the pump source could also be an electrical power supply, a chemical reaction or another laser. The power source inputs energy which is called laser pumping energy, this is what drives the process which produces the laser light. The pumping energy is directed into the gain medium, this is the material which gives different lasers their individual characteristics. There are many different materials used as gain media including crystalline solids usually doped with transition metal ions or rare earth ions, gases such as CO2 or. He, semiconductors such as gallium arsenide and liquids dyes.

6. CARBON DIOXIDE LASERThe carbon dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed (invented by Kumar Patel of Bell Labs in 1964), and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available. They are also quite efficient: the ratio of output power to pump power can be as large as 20%.The CO2 laser produces a beam of infraredlight with the principal wavelength bands centering around 9.4 and 10.6 micrometers

7. CARBON DIOXIDE LASER

8. When energy is pumped into the gain medium it causes the particles in the medium to go into an excited state. Particle in this excited state may drop back to their ground state and when this happens they release their extra energy in the form of a photon of a specific wavelength. This photon may then collide with another particle, if this particle is in its ground state it will absorb the photon and become excited, if the particle is already excited the photon will cause it to drop to its ground state thus emitting another photon, this is called stimulated emission. Photons produced by stimulated emission are very similar to the inittial photon in terms of wavelength, phase and polarisation, this is what gives laser light its characteristics

9. If energy continues to be put into the gain medium then it will reach a state where there are more of the particles are excited then in the ground state, this is called population inversion. This means that a photon passing through the medium has more chance of causing stimulated emission then of being absorbed, the laser is therefore acting as a light amplifier. Mirrors are placed at the front and back of the gain medium. The mirror at the back is fully reflective but the one at the front is only partially reflective. These mirrors will cause photons emitted to pass through the medium many times until they pass through the front mirror and are emitted in the laser beam. This will increase the chance of photons colliding with particles and continuing the chain reaction.

10. SPECTROGRAPHY

11. SPECTROSCOPYMost types of laser are an inherently pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful design of the laser components, the purity of the laser light (measured as the "linewidth") can be improved more than the purity of any other light source. This makes the laser a very useful source for spectroscopy. The high intensity of light that can be achieved in a small, well collimated beam can also be used to induce a nonlinear optical effect in a sample, which makes techniques such as Raman spectroscopy possible. Other spectroscopic techniques based on lasers can be used to make extremely sensitive detectors of various molecules, able to measure molecular concentrations in the parts-per-trillion (ppt) level. Due to the high power densities achievable by lasers, beam-induced atomic emission is possible: this technique is termed Laser induced breakdown spectroscopy (LIBS).

12. A cataract is an opacification or cloudiness of the eye's crystalline lens due to aging, disease, or trauma that typically prevents light from forming a clear image on the retina. If visual loss is significant, surgical removal of the lens may be warranted, with lost optical power usually replaced with a plastic intraocular lens (IOL). Due to the high prevalence of cataracts, cataract extraction is the most common eye surgery. Rest after surgery is recommendedCataract surgery

13. HE- NE LASERThe beam in the cavity and the output beam of the laser, if they occur in free space rather than waveguides (as in an optical fiber laser), are often Gaussian beams. If the beam is not a pure Gaussian shape, the transverse modes of the beam may be analyzed as a superposition of Hermite-Gaussian or Laguerre-Gaussian beams. The beam may be highly collimated, that is, having a very small divergence, but a perfectly collimated beam cannot be created, due to the effect of diffraction. Nonetbeam diameter, and the angle at which the beam eventually diverges varies inversely with the diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon (HeNe) laser spreads to approximately 1.6 kilometres (1 mile) in diameter if shone from the Earth's surface to the Moon. By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost immediately on exiting the aperture, at an. In contrast, the light from non-laser light sources cannot be Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved.

14. USES OF LASER IN LUNAR RANGING

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