Synthesis Of Laser

Lasers are devices that produce intense beams of light which are monochromatic, coherent, and highly collimated, the wavelength of laser light is extremely pure when compared to other sources of light, and all of the energy that make up the laser beam have a fixed phase relationship with respect to one another. Light from a laser typically has very low divergence and can travel over great distances or can be focused to a very small spot with a brightness which exceeds that of the sun. Because of these properties, lasers have found uses in many fields. As a device, it is now used in medicine, astronomy, geodesy, metrology, chemistry, biology, spectroscopy, holography, power engineering, in various processes in engineering, as well as in communication

In many ways, medical applications are like materials processing applications. In some cases material is ablated. In others tissue is cut or welded, and in yet others, photochemical changes are caused in blood vessels to encourage shrinkage and absorption. Understanding tissue absorption characteristics and reaction to wavelength and power are key.Ultraviolet excimer lasers are used for vision correction because they can ablate material from the lens of the eye without causing thermal damage which could blur vision or make the lens opaque[11].Ruby lasers are used for tattoo removal because many of the dyes break down when exposed to 694-nm radiation, yet the skin tissue is left undamaged[5]. Cosmetic treatment of wrinkles, moles, warts, and discolorations (birth marks) is often accomplished with near infrared and infrared lasers. These procedures are often assisted by topical or injected photosensitive chemicals that assist with selective absorption at specific

Intra beam viewing of a point source of light produces a very small spot on the retina resulting in a greatly increased power density and an increase chance of damage. A large source of light such as a diffuse reflection of a laser beam produces light that enters the eye at a large angle is called an extended source. An extended source produces a relatively large image on the retina and energy is not concentrated on a small area the retina as in a point source.

Absorption of Radiation by the Eye

Certain areas of the eye absorb more light in one spectral region than in other regions. Absorption of laser radiation above a certain level leads to tissue injury. Shorter wavelengths of ultraviolet (UV-C and most UV-B), which range from 315 nm to 280 nm for UV-B and 280 nm to 100 nm for UV-C, are absorbed primarily in the cornea .Longer wavelengths of ultraviolet light (UV-A), which range from 400 nm to 315 nm, are absorbed principally in the lens of the eyeball. Radiation in the visible and IR-A (400 nm to 1400 nm) is the most hazardous and is transmitted by the optical components of the eye. It eventually reaches the retina, where most of the radiation is absorbed in the retinal pigment epithelium and in the choroid, which is a dark brown layer with exceptionally large blood vessels and high blood flow rate. Some infrared