By John Oncea, Editor
Green lasers are growing in popularity because the human eye is especially sensitive to green light, which appears almost 30 times brighter than the red color. Does that make them a better choice than red lasers? Maybe yes … maybe no.
There I am, on a Zoom call with my colleague and all-around good guy Geoff Tecza, who asks me, “Have we written anything about green lasers? That could make for a pretty interesting article.” I knew about the Green Lantern, Green Hornet, and Green Arrow. Heck, I even knew about the Jolly Green Giant. But green lasers? Yeah, that was a new one.
So, feel free to jump ahead a section if you already understand what green lasers are but, if you’re like me, read on for a quick tutorial on this technology commonly used in astronomy, pointing devices, alignment tools in construction and manufacturing, and even in some medical procedures.
There are two primary colors most people think of when discussing lasers: red and green. Both types of lasers, despite having different wavelengths, share several similarities:
- Basic Functionality: Both red and green lasers operate based on the same principles of stimulated emission and amplification of light through a lasing medium (such as a crystal or gas).
- Energy Source: They often use the same or similar power sources, such as diodes, to excite atoms within the lasing medium.
- Optical Components: The optical components used in both types of lasers, like mirrors and lenses, can be similar or interchangeable in some cases.
- Applications: Both red and green lasers find applications in various fields such as astronomy, medicine, communication, surveying, and entertainment (like laser shows).
- Safety Measures: Similar safety precautions are necessary for both types of lasers as they can cause damage to the eyes and skin if not used properly.
- Beam Characteristics: In terms of beam characteristics, both red and green lasers produce coherent, monochromatic light with a narrow beam divergence.
However, there are significant differences between the two laser types, the most significant being their wavelength. Red lasers typically have longer wavelengths, around 620-750 nanometers, while green lasers have shorter wavelengths, typically around 495-570 nanometers. This difference in wavelength affects their visibility with green light, being closer to the middle of the visible spectrum, often more visible to the human eye than red light, which may appear dimmer at the same power level.
The different wavelengths also mean that red and green lasers interact differently with various materials. For example, green light might be more easily absorbed or scattered by certain substances compared to red light.
While both types have various applications, the choice of laser color often depends on the specific requirements. Green lasers, due to their higher visibility, are commonly used in astronomy, pointing devices, and certain medical procedures where precise visibility is crucial. Red lasers are also used in similar applications but might be preferred in scenarios where lower cost or specific wavelength characteristics are more important than maximum visibility.
Historically, green lasers were more expensive and challenging to produce compared to red lasers. This was due to the complexity of creating a green wavelength from semiconductor materials. However, advancements in technology have reduced this gap, making green lasers more accessible.
Finally, according to MedCrave, green lasers are more damaging to the retina than red lasers. Green laser pointers operate at 490–575 nm, while red laser pointers operate at 635–750 nm. Consequently, safety regulations and guidelines might vary slightly between the two.
Kermit’s A Liar: It Is Easy Being Green
Green lasers are used for various applications, including laser pointers, laser projection displays, printing, interferometers, bio instrumentation, medical scanning, and pumping of solid-state lasers. They are created using a semiconductor diode laser, typically by doubling the frequency of an infrared laser using a nonlinear optical crystal. This process generates light with a wavelength of around 532 nanometers, which falls within the green region of the visible spectrum.
Green lasers have gained popularity due to their visibility to the human eye. The human eye is more sensitive to green light compared to other colors, making green lasers appear brighter and more visible even at lower power levels compared to lasers of other colors. These lasers have various applications across different fields, including:
- Pointers and Presentations: Green laser pointers are commonly used in presentations, astronomy, and lectures due to their visibility over long distances.
- Astronomy: Astronomers often use green lasers to point out stars or celestial objects during presentations or to assist in aligning telescopes.
- Surgery and Medicine: Some medical procedures, like dermatological treatments or certain types of eye surgery, use green lasers for their precision.
- Research and Education: Green lasers are used in various scientific research applications, including spectroscopy, microscopy, and optical experiments.
- Entertainment and Light Shows: Green lasers are also used in concerts, clubs, and other entertainment venues for light shows and special effects.
Underwater Laser Cutting And LiDAR: Going For The Green
While there are numerous ways in which green lasers can be deployed, let’s take a look at two specific use cases: LiDAR and underwater laser cutting which, according to Laser Systems Europe, is benefitting from an energy-efficient process that has been developed using kilowatt-level green lasers. The process can be used to safely decommission old nuclear power plant structures or cut the steel frames surrounding offshore wind turbines to increase their power output.
“Traditional laser metal cutting typically occurs in dry environments using infrared or other long-wave laser radiation, which requires auxiliary gases delivered coaxially to the beam via intricate piping systems to expel the molten metal produced,” writes Laser Systems Europe. “If such wavelengths are used underwater, however, the light is scattered in all directions, causing substantial power loss over short distances.”
Now, a process developed by Fraunhofer IWS researchers uses short-wavelength green lasers exceeding 1kW of power instead to penetrate water with minimal power loss. “The process requires comparatively little energy, and the power transmission is more efficient,” said project leader Dr Patrick Herwig, who heads the Laser Cutting Group at Fraunhofer IWS.
The technique of using green lasers can be applied in nuclear decommissioning, which helps to effectively cut structures without releasing any hazardous particles into the atmosphere. This technique is also useful in removing the melted residue more efficiently in underwater cutting applications without the need for auxiliary gases, which eliminates the requirement for complex piping. Additionally, since this process is non-contact, it eliminates the need for continuous blade replacement, which is often the case with sawing.
LiDAR is an advanced remote sensing technique that uses pulsed laser light to measure distances and generate a three-dimensional analysis of the targeted area, writes AZO Optics. Green lasers are preferred in bathymetric LiDAR due to their advantages over traditional red or near-infrared lasers. The primary advantage of green lasers is their ability to penetrate water, which allows for measuring the depths of rivers, shallow water reservoirs, and coastal seawater up to three Secchi depths.
"Green lasers exhibit strong compatibility with commonly used silicon-based photodetectors due to their wavelength aligning with detector sensitivity," AZO Optics notes. "This synergy improves photon capture, enhancing signal quality, signal-to-noise ratio, and efficiency."
The use of green lasers in LiDAR systems has several advantages. The shorter wavelength of green lasers allows for more concentrated energy in each pulse, resulting in an extended detection range without compromising the accuracy of the data. This feature is particularly beneficial for applications that require long-range capabilities. Additionally, the heightened visibility of green lasers is noteworthy, as the human eye is more sensitive to green light. This sensitivity leads to better alignment, calibration, and efficiency in underwater LiDAR operations.