•  The word laser is an acronym, which stands for light amplification by stimulated emission of radiation.
• A laser differs from natural light in three ways:
• Lasers emit intense parallel beams of single-frequency radiation (light). Natural light disperses widely as it travels.
• Laser light is essentially monochromatic. Natural light contains a wide spectrum of wavelengths.
• Laser light is coherent and its photons oscillate synchronously. In natural light the photons oscillate randomly.
• Lasers are light beams that are powerful enough to travel miles into the sky and cut through lumps of metal.
• The first practical laser was built by Theodore H. Maiman at Hughes Research Laboratories in 1960.

A laser system is composed of four different parts: 

• The first part is the laser medium, which may be a gas, liquid, or solid.
• In solid medium lasers, ionic impurities known as dopantsare used to generate the laser light.
• An example of a laser with a dopant is the neodymium-yttrium-aluminum-garnet (Nd-YAG) laser.
• The dopant determines the wavelength of the emitted radiation.
• The second portion is the optical cavity wherein the laser medium is confined.
• One of the mirrors in the optical cavity allows the laser beam to escape the cavity instead of being reflected by the other mirrors.
• The third portion of the laser system is a pumping source, which supplies electrical discharge or high-energy photons from a xenon flash lamp.
• The fourth portion is a light guide, which directs the laser beam to the site of surgery. 

Laser work:

• The output of a laser is a coherent electromagnetic field.
• In a coherent beam of electromagnetic energy, all the waves have the same frequency and phase.
• A basic laser consists of a chamber known as the cavity which is designed to reflect infrared, visible or ultraviolet waves so that they reinforce each other.
• The cavity can contain solids, liquids or gases.
• The choice of the cavity material determines the wavelength of the output.
• Mirrors are placed at each end of the cavity.
• One of the mirrors is totally reflective, not allowing any of the energy to pass through them.
• The other mirror is partially reflective, allowing 5% percent of the energy to pass through them.
• Through a process known as pumping, energy is introduced into the cavity through an external source.
• Due to pumping activity, an electromagnetic field appears inside the laser cavity at the natural frequency of the atoms of the material that fills the cavity.
• The waves are reflected back and forth between the mirrors.
• The length of the cavity is such that the reflected waves reinforce each other.
• The electromagnetic waves in phase with each other emerge from the end of the cavity having a partially reflective mirror.
• The output is a continuous beam, or a series of brief, intense pulses.

Characteristics of Lasers:

• We can separate the characteristics of laser beam into four major categories as:
• Superior Monochromatism
• Superior Directivity
• Superior Coherence
• High Output
• Using these characteristics of lasers, they are applied in various fields such as optical communication and defence.
• In the next section, let us look at the various applications of lasers.

Uses of Laser:

• When lasers were first invented, they were called “a solution looking for a problem”.
• Since then they have become ubiquitous finding utility in various applications of modern society ranging from consumer electronics to the military.

Tools:

• CO2 lasers are widely used in industries.
• They are precise, easy-to-automate and don’t need sharpening, unlike knives.
• We use robot-guided lasers to cut pieces of cloth to make things such as denim jeans than using our bare hands.
• They are faster, more accurate and improve efficiency and productivity.
• The same precision is of utmost importance in the field of medicine.
• Doctors use lasers for everything from blasting cancerous tumors to correcting defective eyesight.

Communication:

• The barcode scanner uses a laser to convert a printed barcode into a number that a checkout computer can understand.
• Every time you play a CD or a DVD, a semiconductor laser beam bounces off the spinning disc to convert its printed pattern of data into numbers; a computer chip converts these numbers into movies, music, and sound.
• Lasers are used in fibre optic cables and a technology known as photonics which uses photons of light to communicate.

Defence:

The military uses laser guided weapons and missiles.

Difference between a Flashlight and Laser: