Lasers are optical amplifications based on the stimulated emission of electromagnetic radiation. It creates a highly focused, powerful beam of light with many applications from printing to space exploration.
The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. While ordinary light sources emit light randomly in all directions, a laser concentrates light into a narrow intense beam.
Lasers produce coherent light. Light waves are uniform, traveling in a straight direction with the same frequency and phase.
Types of Lasers
Lasers are classified based on their gain mediums and applications.
Solid-State Lasers
These lasers use solid materials as gain mediums. For example, a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is preferred for surgeries and manufacturing due to high power output and versatility.
Doping is the addition of elements or impurities to alter the state or properties of other materials. Neodymium, a rare earth element, is a common doping agent or dopant for laser production.
Gas Lasers
Gas lasers use a mixture of gases. A well-known type is the carbon dioxide (CO2) laser for cutting, welding, and engraving materials. These lasers can deliver power outputs to several kilowatts.
Semiconductor Lasers
Commonly known as laser diodes, these are small and efficient, used in devices such as DVD players and barcode scanners. They can be made compact and mass-produced.
Fiber Lasers
Using optical fibers as the gain medium, fiber lasers are known for their efficiency and versatility. They're favored in telecommunications and medical technology, and make precise and high-quality cuts.
Laser Components
Gain Medium (Active Medium)
This is solid, liquid, or gas. Its atoms, molecules, or ions can be excited to higher energy levels.
Here light is amplified. When energy is added to the gain medium, its atoms are energized. In solid-state lasers, crystals like ruby or neodymium-doped glass are used, producing red or infrared laser light.
When the excited atoms return to their normal state, they release energy as light. The color and wavelength depend on the type of gain medium. Helium-neon lasers produce red light. Carbon dioxide (CO2) lasers emit infrared.
The Pump
To make light, the gain medium needs an external energy source. Energy can be supplied by electrical currents, another laser's light or chemical reactions. CO2 lasers generally use electrical methods for pumping.
The type of pump depends on the gain medium.
Optical Pumping: Using intense light from flash lamps or other lasers.
Electrical Pumping: Applying an electrical current, as in semiconductor lasers.
Chemical Pumping: Using chemical reactions to excite the medium.
Optical Resonator (Mirrors): This consists of two mirrors placed at either end of the gain medium. One mirror is highly reflective while the other is partially reflective, allowing a controlled fraction of the light to escape. This creates a feedback loop to amplify the light.
Stimulated Emission
Excitation: The energy pump excites the gain medium's particles, causing them to jump to higher, unstable energy levels. This process is called population inversion because normally, most particles are in their lower energy state.
Spontaneous Emission: Some excited particles will spontaneously decay back to their lower energy level, releasing a photon (particle of light) in a random direction.
Stimulated Emission: If a photon of the correct wavelength encounters an excited particle, it stimulates the particle to decay back to its lower energy level. Stimulated decay releases another photon identical to the original photon.
Amplification and Coherence: The photons bouncing back and forth between the mirrors repeatedly stimulate more emission, exponentially increasing the light intensity.
Because the stimulated photons are identical to the original photons, the resulting light is coherent. All the light waves are in phase, creating a well-defined beam.
The photons continue to bounce between the mirrors of the optical cavity, creating more stimulated emissions. The amplification continues until there are enough photons to generate a strong beam of laser light.
Output: Once a sufficient number of photons are produced, they escape through the partially reflective mirror. This produces the narrow, focused beam characteristic of lasers.
Uses
Medicine: Precise surgeries, laser eye correction, dermatological treatments. Lasers enable LASIK eye surgery and skin resurfacing.
Industry: In manufacturing, lasers are favored for cutting, welding, and engraving. Their can create intricate designs to improve production quality and reduce waste.
Telecommunications: Lasers are used in fiber-optic communications. Data can be transmitted over long distances at up to 100 gigabits per second.
Science: Spectroscopy, microscopy, laser-induced fusion.
Weapons: Laser weapons include Singapore's Iron Beam; anti-drone systems and the now defunct US/Israeli laser used to shoot down rockets and artillery shells. In warfare lasers are used in mapping and targeting.
Consumer Electronics: DVD players, laser pointers, barcode scanners, concert light shows and high definition visuals from laser projectors are just some of their current uses.
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