LASER TECHNOLOGY.pptx (Size: 379.84 KB / Downloads: 262)
LASER means “Light Amplification by Stimulated Emission of Radiation”.
A laser is a device that emits light (electromagnetic radiation) through a process called stimulated emission.
The term laser is an acronym for “light amplification by stimulated emission of radiation”.
Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low-divergence beam, or can be converted into one with the help of optical components such as lenses.
They have the same frequencies and identical phase.
A laser consists of a gain medium inside a highly reflective optical cavity, as well as means to supply energy to the gain medium.
The gain medium is a material with properties that allow it to amplify light by stimulated emission.
In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium.
Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.
BASIC MODE OF OPERATION
Light of a specific wavelength that passes through the gain medium is amplified the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly.
Part of the light that is between the mirrors passes through the partially transparent mirror and escapes as a beam of light.
The process of supplying the energy required for the amplification is called pumping.
The energy is typically supplied as an electrical current or as light at a different wavelength.
Continuous wave operation
In the continuous wave (CW) mode of operation, the output of a laser is relatively constant with respect to time. The population inversion required for lasing is continually maintained by a steady pump source.
In the pulsed mode of operation, the output of a laser varies with respect to time, typically taking the form of alternating 'on' and 'off' periods.
In many applications one aims to deposit as much energy as possible at a given place in as short time as possible.
In this mode of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flashlamps, or another laser which is already pulsed.
Pulsed pumping is required for lasers which disrupt the gain medium so much during the laser process that lasing has to cease for a short period.
Even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight, when the beam from such a laser hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.