- Laser Definition: A laser is defined as a device that amplifies light by stimulating electromagnetic radiation to emit coherent and focused light beams.
- Components of Laser: The three main components of a laser are the active medium, the pump source, and the optical resonator, each playing a crucial role in the amplification and emission of laser light.
- Types of Lasers: Lasers come in various types such as solid-state, gas, dye, excimer, chemical, and semiconductor, each using different materials for the active medium.
- Stimulated Emission: This process involves an incoming photon stimulating an electron to emit a second photon, crucial for creating coherent laser light.
- Practical Applications: Lasers are essential in numerous applications across consumer electronics, medical treatments, industrial processes, and scientific research.
LASER
The acronym LASER stands for light amplification by stimulated emission of radiation. A laser uses optical gain to produce a directed beam. Compared with many ordinary light sources, its output can have a narrow spectral linewidth, high spatial and temporal coherence and low beam divergence. Real lasers have finite linewidth, coherence length and divergence set by the laser design. These measurable properties are the characteristics of LASER output.
Most lasers obtain net optical gain by creating a population inversion. For a selected transition, more atoms, molecules or charge carriers occupy the upper laser level than the lower level. An excited system can decay without an incident photon, producing spontaneous emission.
In stimulated emission, an incident photon drives an excited system to a lower energy state and produces another photon matched to the transition. Repeated passes through the gain medium amplify resonant optical modes. Coherence describes correlation in the resulting field and cavity modes over a finite time and distance.
Albert Einstein described stimulated emission in 1917. Charles Townes and Arthur Schawlow published an optical-maser proposal in 1958, and Theodore Maiman demonstrated the first working ruby laser in 1960.
Laser applications include optical storage, printing, barcode scanning, surveying, communications, materials processing, measurement and research. Medical systems use selected wavelengths and pulse formats for procedures such as cutting, coagulation and tissue treatment. A laser’s narrow beam can also damage eyes or skin, and some high-power systems create fire or reflection hazards. Product class, wavelength, output, exposure duration and beam access determine the required controls.
Components of LASER
A conventional laser oscillator has three functional components:
- A lasing material or active medium.
- A pump or energy source.
- An optical resonator or feedback structure.
- The pump transfers energy to the active medium so stimulated emission can provide net optical gain at selected wavelengths. Semiconductors, organic dyes, gas mixtures and doped solids are common media. Examples include He-Ne gas, CO2 gas, Nd:YAG and chromium-doped sapphire, or ruby. Many lasers are named after their active species or host.
- The pump source supplies the energy needed for gain. Pumping methods include electrical injection, gas discharge, flash lamps, arc lamps, another laser and chemical reactions. The suitable method depends on the active medium and required operating mode.
- The resonator provides optical feedback and selects modes that meet its gain and phase conditions. One output path transmits part of the circulating field as the useful laser beam.
A common resonator uses two aligned mirrors around the active medium. One has high reflectivity, while the output coupler transmits a controlled fraction. Light that matches a supported cavity mode makes repeated passes through the medium and can gain more energy than it loses. Laser oscillation starts when round-trip gain exceeds loss and then settles as gain saturates. Semiconductor lasers may use cleaved facets or integrated gratings instead of separate mirrors.
Types of LASER
Lasers can be grouped by active medium, excitation method, wavelength and operating mode. The following list uses active-medium families.
- Solid State LASER
A solid-state laser uses ions embedded in a solid host as its active medium. Examples include ruby and neodymium-doped YAG, or yttrium aluminium garnet. - Gas LASER
Gas lasers use an atomic, ionic or molecular gas as the active medium. He-Ne lasers use a helium-neon mixture, while argon-ion, krypton-ion, CO2, nitrogen and other gas lasers use different species and transitions. - Dye or Liquid LASER
A dye laser uses an organic dye, such as Rhodamine 6G, dissolved in a liquid solvent. Its broad gain spectrum allows wavelength tuning with a dispersive resonator element. - Excimer LASER
Excimer and exciplex lasers use short-lived excited molecular complexes. Common rare-gas-halide media combine a rare gas with a halogen donor and emit ultraviolet light. - Chemical LASER
A chemical LASER obtains pumping energy from a chemical reaction. Examples include the chemical oxygen iodine laser, all gas-phase iodine laser, hydrogen fluoride laser and deuterium fluoride laser. - Semiconductor LASER
These lasers use a semiconductor junction as the gain medium. The Semiconductor structure contains p-type and n-type regions and confines carriers and light in an active layer. Injection laser diodes begin lasing when forward current raises optical gain above cavity loss.
