Lasers are all around us. From the world of industry (automotive, tools, hydraulics, and home appliances) to medicine and beauty, lasers are used practically everywhere because they are versatile and capable of performing many different jobs: cutting, welding and laser marking, tattoo removal, eye surgery, hair removal, etc. Of course, not all lasers are equal, and lasers are chosen based on which has the most suitable source for the job.
There are five types of lasers:
These five types of lasers can be further broken down based on how they work: continuous-wave lasers and pulsed lasers. There are also different types of pulsed lasers. A fiber laser made for to marking can have a variable pulse rate (MOPA) for marking plastic without burning it or leaving burrs.
Before we explain the different types of lasers, let us define what a laser is and how it works.
A laser is a device that generates light in a laser beam. A laser beam is different from a light beam because its rays are monochromatic (a single color), consistent (the same frequency and wave shape), and collimated (all headed in the same direction).
Lasers provide this “perfect information”, ideal for high-precision applications.
In this article, we discuss the History of the Laser, from Einstein to Gordon Gould. Now, let’s take a technical look at the parts of a laser. There are three main components of a laser:
The energy source pumps light in an active medium (the active medium results from the emissions stimulated by photons through electronic or molecular transitions from a lower energy state to an energy state that is higher than the one previously populated by a source). It varies based on the type of laser. It could be a diode laser, an electric shock, a chemical reaction, a flashing light, or other types.
The active media emits a light beam at a specific wavelength when excited by light. This is called the source of optical gain. Lasers often take their name from the gain medium. In a CO2 laser, for example, the gain medium is CO2 gas.
The optical cavity amplifies the optic gain using mirrors surrounding the gain medium, which could be discrete mirrors in solid-state lasers, cut or coated facets in diode lasers, and Bragg reflectors in fiber lasers.
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The industrial CO2 laser sends an electrical current through a gas to generate light through a process known as population inversion. Examples of gas lasers are carbon dioxide (CO2) lasers, helium-neon lasers, argon lasers, krypton lasers, and excimer lasers.
Gas lasers are used in a wide range of applications, including holography, spectroscopy, barcode scanning, measuring atmospheric pollution, materials processing, and laser surgery.
CO2 lasers are probably the best-known gas lasers and are primarily used for laser marking, laser cutting, and laser welding. With the FlyCO2, LASIT can mark natural materials like wood and bamboo. This is very useful in the promotions industry.
Solid-state lasers use ion-doped crystals or glass. This makes them different from dye lasers that use an organic dye (usually in a liquid solution) as the light amplification medium and from gas lasers where an electric discharge in a suitable gas (for example, helium-neon) is used to produce coherent light.
A fiber laser is a special type of solid-state laser in a category of its own. “A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium, and holmium.”
Optical fiber light-guide properties make this laser type different from others. The laser beam is smaller than other laser types, making it more precise. Fiber lasers are also well-known for their small size, good electrical efficiency, low maintenance, and low operating costs.
Fiber lasers are used in a wide range of applications, including materials processing (laser cleaning, texturizing, cutting, welding, and marking), medicine, and directed-energy weapons. This article discusses the advantages of fiber lasers for laser marking, while this article explores the differences between a fiber laser and a variable pulse (master oscillator power amplifier (MOPA)) laser.
Today, fiber lasers are the most common lasers used for laser marking and engraving. They have a long-lasting, high-quality effect on all metals and almost all types of plastic. With this system type, we can also guarantee absolute black markings, without glare, needed primarily in medicine (for safety reasons) and in home appliances and jewelry (for aesthetics).
Another type of laser with a distinctive pulse duration is the Picosecond laser. The FlyPico can make high-contrast absolute black markings without glare. This is very useful in medicine (for safety) as well as in home appliances and jewelry (for aesthetics).
The gain medium for liquid lasers is an organic liquid dye. These lasers are also known as dye lasers and are used in laser medicine, spectroscopy, birthmark removal, and separating isotopes.
One of the advantages of liquid lasers is that they can generate a much wider range of wavelengths, making them good as tunable lasers. This means that the wavelength can be controlled during operation.
For example, when separating laser isotopes, lasers tune in to specific atomic resonances. They are tuned to a specific isotope to ionize atoms, making them neutral charges rather than negative or positive. Then, they are separated with an electrical field to obtain isotropic separation.
A laser diode (or LD) is an optoelectronic device that can emit a laser beam emitted by the active region of the semiconductor from which the device is made. The semiconductor structure is very similar to the one used for making LEDs (Light Emitting Diodes).
Like many other electronic devices, a laser diode consists of a doped semiconductor material in a very thin layer on the surface of the crystal. The crystal is doped to produce a type n region semiconductor and a type p region semiconductor, one on top of the other, to obtain a PN junction, that is, a diode.
Like other diode types, when the structure is polarized directly, the electron holes from the p region are injected into the n region, where the electrons carry most of the charge. Similarly, the electrons in the n region are injected into the p region, where the holes carry most of the charge. When there is an electron and a hole in the same region, they can combine for spontaneous emission. That is, the electron can occupy the energy state of the hole, emitting a photon with energy equal to the difference between the state of the electron and the hole involved.
These injected electrons and holes represent the diode injection current, and the spontaneous emission gives the diode laser under the laser threshold properties similar to an LED. Spontaneous emission is needed to initiate laser oscillation but causes inefficiency once the laser is oscillating.
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