Lasers are high-energy beams of light that serve various purposes, ranging from communication and surgeries to industrial cutting and welding applications.
However, each application requires a specific type of laser that fits its requirements.
There are primarily 5 types of lasers that can be distinguished on the basis of their laser source and mode of operation.
This article discusses the types of lasers, their differentiation based on their mode of operation, and the classification of lasers.
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Types of Lasers
Lasers are classified into five main types:
|Laser||Wavelength (nm)||Few Applications|
|Gas Lasers||190-10600||Microscopy, material processing|
|Solid-state Lasers||300-2800||Spectroscopy, LIDAR|
|Fiber Lasers||780-2200||Metal processing|
|Liquid Lasers||400-1000||Spectroscopy, medicine|
|Semiconductor Lasers||410-2000||Optical disc reader, material processing|
Types of lasers and their applications
The term "LASER" stands for Light Amplification by the Stimulated Emission of Radiation.
Lasers are high-energy radiations that are generated by supplying energy to activate a substance, called gain medium or laser medium.
The molecules of this activated gain medium then release the excess energy in the form of energy radiations ranging from UV to far-infrared wavelengths.
Based on their source, there are four major types of lasers: Gas, solid-state, liquid, and semiconductor lasers.
Each of these lasers has distinct features which make them ideal for different applications.
Gas lasers are generated by passing electricity through a gaseous medium in a closed chamber, and the process of supplying energy to a laser medium is called pumping.
The gaseous medium can either be a pure gas or a mixture of gases at low pressure.
Different types of gas lasers operate at different wavelengths, such as Excimer lasers operating in the UV range and CO2 lasers operating in the far-infrared range of the electromagnetic spectrum.
CO2 lasers are one of the most commonly used gas lasers.
They operate at a wavelength of around 10,600nm, which is readily absorbed by organic materials. Thereby making them ideal for medical applications.
Moreover, the availability of these lasers in high power outputs makes them extremely popular in manufacturing industries.
These lasers are used for industrial applications like cutting and engraving different types of materials, except metals.
However, high-powered CO2 lasers overcome this drawback and can be used for performing through cuts even in metals, making them ideal for industrial laser cutters.
Another common Gas laser is HeNe (Helium-Neon) laser, which operates in the visible spectrum and can be seen as a red light.
HeNe lasers are often used in metrology, confocal microscopy, imaging, medical applications, etc.
Solid-state lasers consist of a host commonly made of glass or crystal, doped with impurity ions from transition metals or rare-earth metals.
Population inversion in solid-state lasers can either be achieved by optical pumping with the help of a flashlamp or by direct pumping from a different laser, such as a diode laser.
The host of a solid-state laser must have some unique lattice, optical, and thermal properties.
Solid-state lasers can reach very high levels of peak power, but it also makes it difficult to cool down the laser medium, which in turn curbs the repeatability and average power.
These lasers operate in a wide range of wavelengths with Ce:LiSAF lasers at 0.3 μm, Nd:YAG lasers at around 1 μm, and Cr:ZnSe lasers operating at around 3 μm.
The flexibility in power and wavelengths allows solid-state lasers to be used in several applications, including medical applications, material processing, multi-photon microscopy, and LIDAR (Light Detection And Ranging).
Fiber lasers are one of the most popular solid-state lasers.
The host medium in fiber lasers is generally glass, and the impurity ions (from rare-earth elements like Yb, Er, and Tm) are doped into the core of the glass medium.
The fiber laser is usually pumped by a diode laser and the light is guided through a fiber-optic cable.
In the optical cable, the light is amplified and tuned to produce a specific wavelength before being delivered to the laser head.
The use of glass optical fiber enhances the precision of the laser, making it more efficient than other lasers.
Fiber lasers can be operated in both pulsed-wave and continuous-wave modes depending on the peak power required.
These lasers have a wavelength of around 1060nm, making them suitable for metal laser engravers and cutters, suitable for materials such as brass, aluminum, copper, silver, gold, etc.
Fiber lasers are not usually effective in cutting or engraving non-metals. However, a modified fiber laser, MOPA Fiber laser can work on plastics and produce colored laser engraving on certain materials.
Continuous-wave fiber lasers are recommended for industrial applications like laser engraving, cutting, drilling, and welding of metal workpieces, where high efficiency and speed are required.
Whereas pulsed-wave fiber lasers are suitable for applications that require high peak power and precision, such as making intricate cuts on hard materials.
Liquid Lasers (Dye Lasers)
Liquid or Dye lasers use a complex organic dye made from dye solutes, like rhodamine 6G or fluorescein, mixed in a solvent at a concentration of about 100ppm.
These lasers are typically pumped by flashlamps or other lasers such as Nd: YAG lasers, diode lasers, excimer lasers, etc.
Liquid lasers can also be tuned to operate in a wide range of wavelengths (from UV to far-infrared) by using different types of dye molecules.
One of the greatest advantages of these lasers is that their wavelength can be changed while the laser is in operation.
This makes dye laser suitable for spectroscopy, isotope separation, removal of scars on the body, treating vascular lesions, astronomy, etc.
Dye lasers require high maintenance as the dye can decompose quickly. Generally, adamantane, an organic compound, is added to the dye to extend its lifetime.
Semiconductor lasers, also called diode lasers, have a PN-junction semiconductor as the gain medium, which, when supplied with electrical energy, causes a spontaneous emission of photons.
These emitted photons have an operational wavelength of 550nm to 950nm and are amplified before being radiated out of the laser module.
However, there are certain semiconductor lasers, such as quantum cascade lasers and optically pumped lasers, that don't have a PN-junction structure and hence can't be called diode lasers.
Diode lasers have a low power output but are compact in design, making it possible to stack them together and produce a higher-energy laser beam.
Semiconductor lasers are generally used as a pumping source for other lasers. They are also used in laser printers, laser pointers, scanners, barcode readers, etc.
These low-powered lasers also have applications in dentistry and soft tissue oral surgeries.
Apart from this, diode lasers are also used in industrial applications involving cutting and engraving of both metals and non-metals, but cannot be used on transparent workpieces such as clear glass.
Although diode lasers provide vast material flexibility, their low power output is not ideal for high-volume industrial applications.
Mode of Operation of Lasers
|Mode of Operation||Characteristic|
|Continuous Wave||Constant power, higher average laser output|
|Pulsed Wave||Pulses of fixed duration, lower average laser output|
Mode of operation of lasers
Lasers can be used both in continuous-wave or pulsed-wave mode, depending on the requirement.
Continuous Wave Lasers
Continuous-wave lasers emit a constant energy beam throughout the operation of the laser.
These lasers provide a comparatively higher power output and are therefore used for applications like cutting and welding of materials.
As the name suggests, pulsed-wave lasers emit short-duration pulses of high-energy lasers. The laser energy increases gradually until the peak power is achieved.
This type of laser has lower average power than continuous-wave lasers hence is suited for spot welding and laser engraving.
Laser beams can be converted to pulses using different methods such as q-switching, mode-locking, gain-switching, etc.
Pulsed-wave lasers can further be differentiated on the basis of their pulse duration - milliseconds, microseconds, nanoseconds, picoseconds, and femtoseconds.
The table below lists different types of pulsed-wave lasers and their applications.
|Milliseconds (10-3 seconds)||Laser hair removal|
|Microseconds (10-6 seconds)||Spectroscopy|
|Nanoseconds (10-9 seconds)||Material processing, remote sensing|
|Picoseconds & Femtoseconds(10-12 & 10-15 seconds)||Precise engraving, surgery, communication|
Pulsed-wave laser types and their applications
Laser Classification by Safety Norms
Class 1 & 1M
Class 1 and 1M are the least hazardous of all laser types. This class of laser is not harmful even when looked at with the naked eye.
Class 1 lasers emit light in the visible spectrum and have a maximum power output of 0.39 mW.
On the other hand, Class 1M lasers have the same standards as Class 1 lasers, but they are hazardous if viewed through an optical instrument like a magnifying glass.
Examples of class 1 lasers are CD/DVD players, laser printers, etc.
Class 2 & 2M
Class 2 lasers emit light in the visible spectrum and have a laser output power under 1 mW.
They are not safe to be stared for a duration longer than 0.25s. They however don't pose any skin burn hazard.
Class 2M lasers have the same standard as class 2 lasers, although they can be hazardous if viewed through an optical instrument.
Examples of class 2 lasers are barcode scanners used in supermarkets and optical level instrument used in construction.
Class 3R & 3B
Class 3R and 3B emit light in the visible spectrum.
Lasers under Class 3R have an output power of 1mW to 4.99mW, whereas Class 3B lasers have a laser output power range of 5mW to 500mW.
Class 3R lasers are safer as damage due to accidental exposure can be prevented by blink reflex, whereas direct exposure to class 3B lasers can cause instant damage to the eye.
Some applications of class 3 lasers are in spectrometry and stereolithography.
Class 4 lasers are the most hazardous of all lasers and have a laser output power of 500mW or more.
They can cause severe damage to the eyes or skin. Even a reflected beam of this laser can cause damage to your eyes.
This class of lasers is mostly used in material processing applications like engraving and cutting.
Frequently asked questions (FAQ)
What is an Excimer laser?
Excimer laser is a type of gas laser that emits UV radiation with varying power levels. In these lasers, electric current is used for pumping the source, and these lasers typically have an efficiency of 0.2% to 2%. Some common types of excimer lasers are XeF lasers, ArF lasers, and F2 lasers. These lasers are used in UV lithography, laser ablation, laser deposition, laser marking, etc.
What is pumping in lasers?
Pumping in lasers is the process of transferring energy from an external source to a laser gain medium for exciting the atoms and molecules in the medium. Pump sources can either be from a laser, flashlamp, or electric current.
Why do pulsed-wave lasers have lower average power than continuous-wave lasers?
Continuous-wave lasers emit constant radiation at constant power throughout their operation. On the other hand, pulsed-wave lasers emit periodic laser pulses for very small durations, that reduces the average output power of the laser, even though they may have higher peaks than continuous-wave lasers.