Continuous Wave Laser: Definition, How It Works, Types, Applications, and Advantages
Lasers have widespread use in a variety of industries including: medical, fabrication, and scientific research. They are mainly used for cutting, welding, and precise measurement. Continuous wave lasers are a category of laser that provides a steady power output, which contrasts their pulsation wave counterparts. Lasers essentially work by using a light or electrical source to excite a medium that emits photons of a specific wavelength and direction creating a monochromatic light source. The recent development of the ultraviolet laser will see many new applications opened up for continuous wave lasers. This article will discuss the definition, inner workings, types, applications, advantages, and disadvantages of continuous wave lasers.
A continuous wave laser is one of two types of laser, the second being a pulsating laser. It provides a continuous light source, whereas the pulsating laser emits light in pulsating waves. In the case of a continuous wave laser, key parameters including power output and intensity must be kept the same for the duration of the emission. Continuous wave lasers emit monochromatic light—which is light of a singular wavelength.
To understand how a laser works, an explanation of how light works is required. In a normal light bulb, energy is supplied which releases light particles (photons) from the energized material in a spontaneous manner in all directions. To create a coherent light source, these photons are used to excite another material. The chosen material will have two important properties. Firstly, it will only emit photons of the same wavelength, secondly, it will not absorb the primary photon. This means for every photon supplied two are returned. The excited material is usually a crystal or a gas that will produce photons of the same wavelength and direction. The coherent photons are passed back and forth as a beam through the medium using mirrors, any spontaneous photons will travel in a different direction meaning they do not exit with the laser. This leaves a single coherent light source exiting the laser-producing machine.
The purpose of a continuous wave laser is to provide a constant laser output. One important characteristic of a continuous wave laser is it is much easier to work out, and therefore control, exposure time as the energy output is a known consistent value. Whereas for pulsation lasers this is not as easy to work out.
Each of the different types of lasers capable of operating in continuous wave mode is defined here, and its ability to produce continuous waves is explained:
A fiber laser is a laser that has been passed through a fiber optic cable to produce a laser. The internal core of the silica glass optical fiber is doped, usually with Erbium. Erbium is used as it is good at absorbing and emitting photons of the desired wavelength. A light source is pumped into the optical fiber, where stimulation occurs and leads to the emission of the desired light. Light is then amplified through the many reflections occurring in the fiber. A fiber laser is used in laser cutting, drilling, and welding, as well as in optical testing, spectroscopy, and precision measurements.
Gas lasers pass a stimulating light source through a gas medium to excite the gas element and emit photons. The use of different gases gives the gas laser a range of applications. For example, CO2 lasers are used for high-power applications including cutting and welding. Whereas helium-neon lasers are known for alignment and positioning which lends itself to use in scientific and medical instruments.
In a semiconductor laser, a forward bias p-n semiconducting material is used—usually an aluminum alloy and gallium arsenide. The p-type and n-type materials are held apart and a voltage is applied across them. Electrons flow from one side to the other and some excess energy creates photons. The photons interact with incoming electrons to create more photons. The photons travel down the gap between the n- and p-type materials and exit the gap as a laser. Semiconductor lasers have found use in motion sensors, projectors, and headlamps.
Dye lasers simulate a liquid medium to radiate photons. The organic dye within the solution usually degrades from the application of heat, so a reservoir filled with the solution is continuously pumped through the laser. Dye lasers are mostly used for medical purposes including the treatment of scars, fine veins, and birthmarks.
Solid-state lasers use a solid material such as crystals or glass to create a laser. The crystal or glass is doped with rare earth or transition metal ions. A light source is pumped into the crystal or glass medium to stimulate the medium and create photon emission. Solid-state lasers are used in spectroscopy, material processing, and medical applications.
Continuous wave lasers are used for welding and cutting or precision measuring and alignment across multiple industries. The most common industries that use continuous wave lasers are:
- Material Processing
- Medical and Biomedical Applications
- Scientific Research
- Environmental Monitoring
Yes, continuous wave lasers are used in cutting applications. However, pulsating lasers are more common as they can achieve a higher intensity since they are only at that intensity for short periods of time. This means that pulsating lasers can work at a higher intensity without overheating.
Yes, a continuous wave laser can be used for welding. Continuous wave lasers have a high feed-in rate of 100 inches per minute, otherwise, they will overheat the part.
Yes, continuous wave (CW) lasers can be used in surgery. Gas lasers can be used for sealing blood and lymph vessels to prevent the spread of tumor cells. They can also be used for the removal of vascular lesions and tumors. Fiber lasers are also used to seal blood vessels but can also be used to debulk cancers in the lungs, stomach, and urological tract. Dye lasers are used to disrupt blood vessels, and solid-state lasers are used to coagulate them.
A continuous wave laser differs from other lasers as it provides monochromatic light at a constant power output. Other laser types include pulsating and modulating lasers; they differ from continuous wave lasers as they change their output over a given time period. Pulsating lasers release energy in ultra-short pulses which rise and fall in intensity. Modulating lasers are similar to pulsating lasers, however, they are either on or off. Both pulsating and modulating lasers switch between a maximum and minimum energy output whereas a continuous laser stays at a steady maximum.
Any change or degradation to the medium to which power is supplied to create a laser beam will affect the laser's output and stability. Other factors that affect the power output and stability are:
- The temperature of the laser and the environment.
- Poor construction.
- Power supply instability.
The main advantage of continuous wave lasers is their stable power output. Other advantages that can be exploited are:
- They are compact.
- Highly efficient.
- They have a high power density.
- High feed rates for welding applications.
The biggest limitation of the application of continuous wave lasers is their cost. For many possible applications, cheaper alternatives are available. Other limiting factors are:
- Health and safety requirements due to radiation.
- They can cut to a limited thickness in cutting applications.
- Although efficient, they do require a lot of energy.
- They require a stable power source.
The use of a continuous wave deep ultraviolet laser has been demonstrated by Japan’s Materials and Systems for Sustainability. A breakthrough in 2007 enabled researchers to fabricate aluminum nitride. This led to the growth of aluminum gallium nitride which is used to build ultraviolet-emitting lasers. The development of ultraviolet lasers opens up many more possible applications including for sterilization and medical purposes.
Yes, a CW laser operates in both pulsed and continuous modes. However, not all lasers can operate in both modes.
Yes, the power output of a continuous wave laser should be constant over time. The term stability is used to describe a laser's tendency to remain at a constant output over time. It is very important that continuous wave lasers remain at a constant power output as they are designed for their application.
Yes, the power output of a continuous wave laser can be controlled by controlling the input signal into the laser. However, the laser may need some time to stabilize after the adjustment is made.
This article presented the continuous wave laser, explained it, and discussed its various types and applications. To learn more about continuous wave lasers, contact a Xometry representative.
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