The word LASER stands for light amplification by stimulated emission of radiation. It is device which is used to produce the light beam concentrated to a fixed point and having a high power output ranging from Milliwatt to watts. The frequency of the laser beam is from 430 Tera Hz to 750 Tera Hz.
Actually the laser is a device, which is designed to generate a light with special and unique characteristics. The laser was developed by Dr. Theodore Maiman in the spring of 1960. He placed a photographic flash lamp next to a cylindrical crystal of pink ruby. The result of this action produced the first laser. The laser is power full light source and its light is monochromatic, which means that it consists of single color and not a mixture of colors.
The force which is used to compel the electrons to move from lower energy level towards high energy level is known as pump input. This external force may be in the shape of flash of light OR external applied voltage OR magnetic force etc.
When the electrons moves from the lower energy level to high energy level due to pump input, they stay at the high energy band for a movement. That movement at which the access of electron are collected in the high band of energy level is known as population inversion.
Classes Of Laser
Safety standards have placed laser into four classifications according to their potential hazards. These classifications are:
Class - I Lasers
These are those lasers which produce light below a dangerous level.
Class - II Lasers
The class II lasers can damage the human eye only if the eye is deliberately exposed to the beam for the time longer than the normal blinking of the eye. In other words the brightness of the light would cause a normal eye to blink before injuring occurs.
Class - III Lasers
The lasers in this class can produce light of high enough intensity to inure a human eye before the eye can blink.
Class - IV Lasers
All the lasers which are more power full then class III are port of this class. They are great potential hazards to the eye and the exposed skin. They can produce enough light to burn any combustible materials that their beam strike. Thus they are also considered a fire hazard.
In any laser system a hazard even more dangerous then beam itself is the electrical power supply. Voltages in access of 1000 volts are present even in low power lasers.
A class III lasers wil not produce any injury under normal use but potential of up to 5000 volts are present in the power supply which could easily cause serious personal injury. Therefore the laser power supply should always be enclosed in a suitable housing.
Safety Precautions For laser Work
- Do not stare into the laser beam or reflection of beam from shining objects. For class III lasers reflection from a flat mirror type surface is as dangerous as beam itself. However the reflection from diffused surface such as wall are not considered dangerous.
- Don't point the laser at eye. To help avoid this always keep the laser below eye level when the laser is turned ON.
- Don't intentionally or unintentionally track vehicles or air craft with any laser beam.
- Don't leave an operating laser unattended and be sure to disconnect it from its power source, when it is not in use.
- Don't operate the laser with power supply exposed.
- Never attempt to remove the protective housing from the laser trainer. Any attempt to do this could result in a serious electrical shock.
Uses of laser:
There are so many uses/applications of laser such as:
The 1st uses of the laser were dedicated to military applications. which still constitute a major portion of laser use today. Laser mostly in military applications deals with:
- Measuring distances
- Range finding
- Target designation
- Target simulation
The laser also uses in industries. So the industrial applications of laser include
- Heat treating/Hardening
of many varieties of material at speeds and of quality, not available before.
In medical side, the laser has also so many applications such as:
- Laser use for eye surgery
- Laser use for Ear surgery
- Laser use for Internal Surgery
- Laser use for Special treatment of cancers
- Laser use for in host of testing and diagnostic procedures
- Laser user for in Endoscopy
The more applications of lasers are finding day by day with the help of scientific research.
Other uses of laser are
- Now a days it is widely used in communication in order to achieve high speed and more data transfer rate.
- For quality printing we take the help of laser technology and different types of laser printers are designed.
- laser technology is also used for the purpose of reading or writing the text graphics etc. one of the example is the CD ROM drive of computer.
- Now a days the technology of laser is used in different fields of military such as laser guided missiles.
- laser is also used to measure the distance and speed of the object.
- laser technology is used for manufacturing and etching IC's.
Types of laser:
laser's are designed in different types and shapes. A few types of laser's are explained as below.
- Ruby Laser
- Gallium Nearside Laser (Ga As)
- Gallium Phosphate (Ga p)
- Gallium Arsenide Phosphate laser (Ga As p)
- Indium Gallium Arsenide Phosphate
- Aluminum Gallium Arsenide laser (Al Ga As)
The laser speckle makes a reflected laser beam appear to dance.
A low power reflection of laser light appears to be made up of several dark and light spots that dance about almost as if flakes of glitter had been dropped into the beam. This appearance is known as laser speckle and results from the coherence of laser light. Each part of reflection hit by the light acts as a point source of coherent light. Light from each of these point sources moves away from point in circular/spherical direction. If only two of these point sources are present a simple interference pattern results. however there are actually infinite number of point sources in the reflecting spot, each sending out coherent waves interfering with each other. The result is very complex interference pattern in space.
Now speckles are actually the dark and light spots with in this complex interference pattern. As we move these spots also move and dance.
Something General about Laser
We know that the lasers can produce very high concentration of power on relatively small areas. The radiance of even small lasers can exceed that of the sun because the laser beam is so intense. The very bright or high radiance source, the coherent and directional properties of laser light allow the beam to be focused to extremely small spots.
When light energy is directed onto a target, then it is partly absorbed by that target. The observed energy raises the temperature of the target surface at the point of incident. The amount of this temperature increase depends on the concentration of the light energy or irradiance.
Now since the laser beam is brighter than the sun, therefore it greatly increase the temperature of the target upon which it falls.
When laser beam is directed to human skin, then temperature of the skin will increase in the area struck by the beam. If the temperature becomes high enough then skin will burn. This occurs only when the laser power is very large.
Small lasers such as Health Kit ET-4200 will not cause skin burns. However if the beam is focused to a very small spot then irradiance at the focal point increases and so burns skin.
The human’s eye has a very good Lens system, which focuses incoming light to a very small spot on the back portion of eye called retina.
So the low power beams also when focused buy the eye’s Lens then high irradiance values may reach and so it burns a spot on the Retina. This burn can result in a blind spot in a person’s field of vision.