i m in 12th class..and i have to make a physics assignment of atleast 20 pages on topic gas lasers and its application.plz help me to get content on this topic..i had googled on this topic but not sufficiently satisfy with that so plz can you send me some content on it...?? my mail id is \"pankaj.6.gupta@gmail.com\"plz help me out...!!

Dear PAnkaj,

The word "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. Lasers are finding ever increasing military applications -- principally for target acquisition, fire control, and training. These lasers are termed rangefinders, target designators, and direct-fire simulators. Lasers are also being used in communications, laser radars (LIDAR), landing systems, laser pointers, guidance systems, scanners, metal working, photography, holography, and medicine.

The primary wavelengths of laser radiation for current military and commercial applications include the ultraviolet, visible, and infrared regions of the spectrum. Ultraviolet radiation for lasers consists of wavelengths between 180 and 400 nm. The visible region consists of radiation with wavelengths between 400 and 700 nm. This is the portion we call visible light. The infrared region of the spectrum consists of radiation with wavelengths between 700 nm and 1 mm . Laser radiation absorbed by the skin penetrates only a few layers. In the eye, visible and near infrared radiation passes through the cornea, and is focused on and absorbed by the retina. It is the wavelength of the light that determines the visible sensation of color: violet at 400 nm, red at 700 nm, and the other colors of the visible spectrum in between. When radiation is absorbed, the effect on the absorbing biological tissue is either photochemical, thermal, or mechanical: in the ultraviolet region, the action is primarily photochemical; in the infrared region, the action is primarily thermal; and in the visible region, both effects are present. When the intensity of the radiation is sufficiently high, damage to the absorbing tissue will result.

A basic understanding of how a laser operates helps in understanding the hazards when using a laser device. Figure 2 shows that electromagnetic radiation is emitted whenever a charged particle such as an electron gives up energy. This happens every time an electron drops from a higher energy state, Q1, to a lower energy state, Q0, in an atom or ion as occurs in a fluorescent light. This also happens from changes in the vibrational or rotational state of molecules.

The color of light is determined by its frequency or wavelength. The shorter wavelengths are the ultraviolet and the longer wavelengths are the infrared. The smallest particle of light energy is described by quantum mechanics as a photon. The energy, E, of a photon is determined by its frequency, v, and Planck's constant, h.

The velocity of light in a vacuum, c, is 300 million meters per second. The wavelength, , of light is related to v from the following equation:

The difference in energy levels across which an excited electron drops determines the wavelength of the emitted ligh

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