Terminology and History
- The first device using amplification by stimulated emission operated at microwave frequencies and was called a maser.
- When similar optical devices were developed, they were first known as optical masers.
- Today, all devices operating at frequencies higher than microwaves are called lasers (e.g. infrared lasers, ultraviolet lasers, X-ray lasers, gamma-ray lasers).
- Devices operating at microwave or lower radio frequencies are called masers.
- The back-formed verb to lase is frequently used in the field, meaning to give off coherent light.
- The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories.
- Theoretical work by Charles H. Townes and Arthur Leonard Schawlow contributed to the development of the first laser.
- The word 'laser' originated as an acronym for light amplification by stimulated emission of radiation.
- The acronym LOSER (light oscillation by stimulated emission of radiation) has been humorously noted as a more correct option.
- The terms 'laser' and 'maser' are also used for naturally occurring coherent emissions in astrophysical and atom lasers.
- Albert Einstein established the theoretical foundations for the laser and the maser in 1917.
- Rudolf W. Ladenburg confirmed the existence of stimulated emission and negative absorption in 1928.
- Valentin A. Fabrikant predicted the use of stimulated emission to amplify short waves in 1939.
- Willis E. Lamb and R.C. Retherford found apparent stimulated emission in hydrogen spectra in 1947.
- Alfred Kastler proposed the method of optical pumping in 1950.
- Joseph Weber presented the idea of using stimulated emissions to make a microwave amplifier in 1951.
- Charles H. Townes and his team produced the first microwave amplifier in 1953.
- Nikolay Basov and Aleksandr Prokhorov independently solved the problem of continuous-output systems in the Soviet Union.
- Prokhorov and Basov suggested optical pumping of a multi-level system as a method for obtaining population inversion in 1955.
- Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics in 1964.

Fundamentals of Laser Physics
- A laser produces a narrow beam of light in a single wavelength.
- Light and other forms of electromagnetic radiation are described as the group behavior of fundamental particles known as photons.
- Photons are released and absorbed through electromagnetic interactions with other fundamental particles.
- The release of a photon in a laser is triggered by the nearby passage of another photon, known as stimulated emission.
- This process allows for the possibility of a chain reaction, where photons trigger stimulated emission in other atoms.
- Electrons and their interaction with electromagnetic fields are important in understanding chemistry and physics.
- Discrete energy levels of electrons in an atom play a role in absorption and emission of photons.
- Stimulated emission and its characteristics are explained by quantum mechanics.

Design and Characteristics of Lasers
- Lasers are characterised by their coherence, both spatial and temporal.
- Spatial coherence is expressed through the output being a narrow beam, which can be focused to tiny spots or have low divergence.
- Temporal coherence implies a polarised wave at a single frequency, with phase correlation along the beam.
- Lasers can emit a broad spectrum of light or different wavelengths simultaneously.
- Certain lasers are not single spatial mode and have light beams that diverge more than the diffraction limit.
- Gain medium, laser pumping energy, high reflector, output coupler, and laser beam are components of a laser.
- Mode-locked lasers are capable of emitting extremely short pulses.
- The pulses repeat at the round-trip time of the resonator.
- Mode-locked lasers are used in femtosecond physics, femtosecond chemistry, and ultrafast science.
- Titanium-doped, artificially grown sapphire (Ti:sapphire) is a suitable gain medium for mode-locked lasers.
- Consecutive pulses from a mode-locked laser are phase-coherent and identical.

Applications of Lasers
- Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, and fiber-optic communication.
- They are also used in semiconducting chip manufacturing, laser surgery and skin treatments, cutting and welding materials, and military and law enforcement devices.
- Lasers are employed in laser lighting displays for entertainment purposes.
- Semiconductor lasers in the blue to near-UV are used in car headlamps.
- Lasers have replaced light-emitting diodes (LEDs) in some applications to excite fluorescence as a white light source.

Operation and Types of Lasers
- Lasers can operate in continuous or pulsed mode.
- Continuous-wave lasers have constant power output over time.
- Many lasers lase in multiple longitudinal modes simultaneously.
- Pulsed lasers produce optical power in pulses at a certain repetition rate.
- Some lasers cannot be operated in continuous mode due to limitations.
- Pulsed pumping is another method of achieving pulsed laser operation.
- Flash lamps and other pulsed sources are used to pump the laser material.
- Pulsed pumping was historically used with dye lasers.
- Three-level lasers require pulsed pumping.
- Excimer lasers and copper vapor lasers cannot be operated in continuous wave mode.

Laser (Wikipedia)

For other uses, see Laser (disambiguation).

"Lase" redirects here. For uses of "Laze", see Laze.

"Laser beam" redirects here. Not to be confused with LazarBeam or Lazer Beam.

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow.

A laser differs from other sources of light in that it emits light that is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. It also allows a laser beam to stay narrow over great distances (collimation), a feature used in applications such as laser pointers and lidar (light detection and ranging). Lasers can also have high temporal coherence, which permits them to emit light with a very narrow frequency spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond.

Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic, and free-space optical communication, semiconducting chip manufacturing (photolithography), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in the blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source; this permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps.