Light comes in many different wavelengths. Red light has a wavelength of about 700nm and violet light has a wavelength of about 400nm. Orange, Yellow, Green, Blue and indigo have wavelengths between these two. In general, light is made up of a range of different wavelengths. In addition within the light beam, many different phases occur, so that constructive and destructive interference occur within the beam.
Laser is an acronym, standing for 'Light Amplification by the Stimulated Emission of Radiation'. As the name suggests, laser light is a very special sort of light. A laser beam contains only one wavelength of light – it is momochromatic - and all light in the laser beam is coherent, or in phase, so within the beam only constructive interference occurs.
The laser light consists of only one wavelength because of the way it is produced. When an atom absorbs light of a particular frequency corresponding to a transition of an electron in the atom from an energy level to a higher energy level, it becomes excited. The same wavelength of radiation will be emitted when the atom inevitably decays. If other atoms nearby are also excited to the same level, it will be more likely that they emit radiation of the same frequency just because one atom already has: atoms can be stimulated to emit radiation. By means of a technique called pumping, many atoms can be excited to the same energy level, so when the atoms are illuminated with light of the correct frequency they will all decay and the illuminated light can be amplified.
There are many uses of lasers, in all areas of medicine, science, industry and leisure and warfare. These rely on that the power of laser light can be tightly controlled and focused. In air there is very little divergence.
Lasers can be used in the treatment of cancer, to destroy tumours. Lasers can precisely target a tumour, leaving surrounding tissue virtually untouched. This technique is called laser surgery, and tends to produce less bleeding than ordinary surgery because the blood vessels tend to be sealed by the laser. Laser treatments can also be used to correct sight problems, removing the need for glasses or to re – attached a detached retina.
Lasers are used in the bar code scanners used in shops, compact discs, in the pointing devices used in presentations.
They can be used to cut and weld metals, in the manufacture of semiconductors, in surveying.
They can be used in targeting devices to guide a weapon to a target, meaning that the military only kill the innocent people they want to kill.