Laser or Light Amplification by Stimulated Emission of Radiation is a device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation. A laser differs from other sources of light because it emits coherent light. Coherent light is a beam of photons (particles of light) that have the same wavelength and travel in the same phase. In lasers, waves are identical and in phase, which produces a beam of coherent light. The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.

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Light travels in waves, and the distance between the peaks of a wave is called the wavelength. Each color of light has a different wavelength. For example, blue light has a shorter wavelength than red light. Sunlight and the typical light from a lightbulb are made up of light with many different wavelengths. Our eyes see this mixture of wavelengths as white light. Light can be produced by atomic processes, and it is these processes that are responsible for the generation of laser light.

A laser is different from conventional light sources in four ways: 

• Coherence - The light waves of laser light have only one wavelength. Hence, all the photons emitted by laser light are in phase. Thus, laser light is coherent.
• Directionality - The laser beam is very narrow and can be concentrated in a very small area. This makes laser light highly directional.
• Monochromaticity - The light waves from laser contain only one wavelength or color so it is known as monochromatic light.
• High intensity - The laser light spreads in a small region of space. Hence, all the energy is concentrated in a narrow region. Therefore, laser light has a greater intensity than ordinary light.