Laser

A laser is a device that makes a special kind of light. This light comes from a process called optical amplification and something known as stimulated emission of electromagnetic radiation. The word laser is short for "light amplification by stimulated emission of radiation." The first laser was made in 1960 by Theodore Maiman at Hughes Research Laboratories. This was based on ideas from scientists like Charles H. Townes and Arthur Leonard Schawlow.

Lasers are different from normal lights. A laser makes light that is coherent. This means the light waves are organized and travel together. This special light can be focused into a very small spot. This is useful for tasks like laser cutting and making tiny patterns for computer chips. Laser beams can also stay narrow over long distances. This makes them great for tools like laser pointers and devices that measure distances, such as lidar.

Lasers are used in many everyday things. They help with fiber-optic communication, optical disc drives, laser printers, and barcode scanners. They are also used in medicine for laser surgery and skin treatments. In industry, lasers help cut and welding materials. Because they are very precise and powerful, lasers are one of the most important inventions of the 20th century.

Terminology

The first device that used amplification by stimulated emission worked with microwave frequencies and was called a maser. This short for "microwave amplification by stimulated emission of radiation." When similar devices were made to work with light, they were called optical masers. Later, the word "microwave" was changed to "light," and the term laser was born.

Today, devices that work with frequencies higher than microwaves, such as infrared lasers, ultraviolet lasers, X-ray lasers, and gamma-ray lasers, are all called lasers. Devices that work with microwave or lower frequencies are called masers. The verb "to lase" means to give off coherent light, and it describes what happens when a laser is operating.

Fundamentals

Photons, tiny packets of light, are released from atoms and molecules. In everyday light sources like lightbulbs or stars, this light comes from many different energy levels, creating a mix of colors. This is called thermal radiation.

In a laser, the process is different. When a photon passes by, it can make another photon be released in the same way. This is called stimulated emission. If many atoms are in the right excited state, these photons can make even more photons, creating a chain reaction. Special materials in lasers stay excited longer, letting this chain reaction happen. Lasers can focus their light into thin beams or spread it out over long distances, making them different from normal light.

Design

A laser has three main parts: a gain medium, a way to give it energy, and something to keep the light focused. The gain medium is a special material that can make light stronger. When light goes through it, the light gets more powerful.

To make the gain medium work, it needs energy. This energy can come from electricity or another light source. Most lasers have two mirrors on each end of the gain medium. The light bounces between the mirrors and gets stronger each time. One mirror lets some of the light out, creating the laser beam.

Laser physics

See also: Laser science

Electrons and how they interact with electromagnetic fields help us understand chemistry and physics.

Stimulated emission

Main article: Stimulated emission

Electrons in atoms can move between different energy levels. They can take in energy from light or heat, which makes them jump to a higher energy level. Later, the electron can fall back down, releasing a photon of light.

When a photon with the right wavelength hits an excited electron, it can make the electron drop to a lower energy level and give off a new photon. This new photon is just like the one that caused the drop — same wavelength, phase, and direction. We call this process stimulated emission.

Gain medium and cavity

The gain medium is a special material that can make light stronger. It is put into an excited state by an outside energy source, like a light or electrical signal. This material can be a gas, liquid, solid, or plasma. When enough particles are excited, more stimulated emissions happen than absorptions, which makes the light stronger.

The gain medium is placed inside a resonator, which usually has two mirrors. Light bounces back and forth between these mirrors, passing through the gain medium many times. This makes a strong, focused beam of light. If the gain is strong enough, the light can become very powerful.

The light emitted

Most lasers start with a little random light, which is then made stronger by stimulated emission. This makes light that is very pure and focused. Laser light can be very narrow and can stay focused over long distances, though it will eventually spread out due to diffraction.

In 1963, Roy J. Glauber showed how laser light can be described using quantum physics, for which he won the Nobel Prize in Physics. Laser beams can look different and have different properties depending on the design of the laser and its resonator.

Quantum vs. classical emission processes

The making of laser light depends on stimulated emission, a process predicted by Albert Einstein. This process involves electrons moving between energy levels in atoms or molecules. In some special lasers, like free-electron lasers, atomic energy levels are not used, and the process can be explained without quantum mechanics.

Modes of operation

A laser can work in two ways: continuous or pulsed. In continuous mode, the laser beam stays steady. This is good for tasks that need a constant beam. In pulsed mode, the laser sends out bursts of light. This is helpful for special jobs like cutting or studying very fast processes.

Some lasers can switch between these modes. For example, a continuous laser can be turned on and off to make pulses, but it is still called a continuous-wave laser if the pulses are slow. Lasers that need to send out very short, powerful bursts use techniques like Q-switching or mode locking. These methods help create short light pulses, useful for studying fast events in science.

History

In 1917, Albert Einstein described the basic idea for lasers in a scientific paper. He explained how light could be made stronger.

Over the next decades, scientists worked on this idea.

The first real laser was made in 1960 by Theodore Maiman. He used a small piece of ruby crystal to create the first laser beam. Since then, scientists have created many types of lasers using different materials, each with new and helpful abilities.

Types and operating principles

Further information: List of laser types

Gas lasers

Main article: Gas laser

After the invention of the helium-neon gas laser, many other gases have been used to create lasers. The helium-neon laser can work at many wavelengths, but most are made to work at 633 nanometers. These lasers are common in schools and labs. Carbon dioxide lasers can make strong beams used in industries for cutting and welding. Argon-ion lasers can make light in several colors, and nitrogen lasers are often used by hobbyists. Some gas lasers use metals and can make deep ultraviolet light.

Solid-state lasers

Main article: Solid-state laser

Solid-state lasers use materials like crystals or glass that are treated with special atoms. The first laser ever made was a ruby laser. Neodymium is a common material used in solid-state lasers and can make strong infrared light. These lasers are used for cutting, welding, and medical procedures. Other materials like ytterbium and holmium are also used in solid-state lasers for different purposes.

Fiber lasers

Main article: Fiber laser

Fiber lasers use thin glass fibers to guide the laser light. These lasers can make very strong beams and are used in industries and medicine. The fibers help keep the laser cool and reduce distortions in the light beam.

Semiconductor lasers

Main article: Semiconductor lasers

Semiconductor lasers are small devices that use electricity to make light. They are used in laser pointers, CD players, and many other devices. Some semiconductor lasers can make very high power and are used in industries for cutting and welding. Scientists are also working on making lasers from silicon, which could be used in computers.

Uses

Main article: List of applications for lasers

When lasers were first made, people wondered what they could do. Now, lasers are used in many parts of daily life. They help in consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. For example, lasers are important for fiber-optic communication, which helps send lots of information over long distances.

One of the first ways people noticed lasers was in supermarket barcode scanners, starting in 1974. Lasers are also in many everyday devices, like laser printers and CD players. They are used for cutting and shaping materials, helping doctors in surgeries, guiding people, and making fun light shows.

Lasers have many important uses in medicine. They can help fix eye problems, treat kidney stones, and improve skin looks. Lasers are also used to treat some cancers by shrinking or removing growths. This can be done with less pain and scarring than traditional surgery. Doctors need special training to use these laser treatments.

Lasers can sometimes be used as tools to defend against enemies. There are rules, like the Protocol on Blinding Laser Weapons, that stop the use of lasers that can cause lasting harm to vision.

Safety

Even the first laser was known to be dangerous. Low-power lasers can be risky for your eyes if the light beam hits them directly or bounces off a shiny surface. The light from a laser can focus to a tiny spot on the retina, causing burns and permanent damage quickly.

Lasers are grouped into safety classes to show how dangerous they are:

• Class 1 lasers are safe because they are usually enclosed, like in CD players.
• Class 2 lasers are safe for normal use; your quick blink helps protect your eyes. These are often found in laser pointers.
• Class 3R lasers have a small risk of hurting your eyes if you stare at them too long.
• Class 3B lasers can harm your eyes right away.
• Class 4 lasers are very powerful and can burn skin and damage eyes, even from scattered light. Many industrial lasers fall into this category.

People who work with powerful lasers should wear special safety goggles to protect their eyes.