Diode, CO2, Fiber, Blue and Infrared Lasers. What are the differences?

As laser technology continues to advance, there are numerous types of lasers with different names that are sometimes confusing for users to choose.

In this comprehensive guide, we delve into the fundamental theories behind different laser types, including Diode laser, CO2 laser, Fiber laser, Blue light laser, and Infrared laser. We'll explore their features, benefits, and potential drawbacks to help you determine the most suitable option for your needs.

Furthermore, we'll evaluate crucial factors such as general applications, power, speed, maintenance and lifespan, providing valuable insights into each laser type's performance in these areas.

Diode, CO2, Fiber, Blue, Infrared Lasers, what are the differences?

1. 1 The fundamental mechanism

Before we navigate into further topics, it is essential to know about the fundamental mechanism of a laser.

A laser produces a coherent beam of amplified light through a process called stimulated emission. In its basic form, a laser consists of three main components: an optical cavity or resonator, a gain medium, and a pump source.

The gain medium is the material that is stimulated to emit light, such as crystal, gas or dye.

The pump source exciting the gain medium can be a flash bulb, electrical discharge or another laser. The light from the pumped gain medium bounces back and forth between the mirrors of the optical cavity. Each time the light passes through the gain medium, it causes more light of the same wavelength and phase to be emitted. This results in an amplification of the light.

One of the mirrors in the cavity is only partially reflective, allowing the amplified, coherent light to escape as a laser beam. This process produces light that is monochromatic, directional, and coherent.

1. Gain medium
2. Laser pumping energy source
3. High reflector
4. Output coupler
5. Laser beam (source: Wikipedia)

The key of laser operation is the stimulated emission in the gain medium and optical amplification through the cavity. By using different gain medium and pump sources, a variety of laser systems with different output wavelengths and power levels can be developed for different applications.

1.2 Two different categorizations of Lasers

Lasers can be categorized by their gain medium. Common types include gas lasers (like CO2 lasers), solid state lasers (like Diode and Fiber lasers), dye lasers, etc. The gain medium determines many of the properties of the laser like the wavelength(s) of emitted light, maximum power, pulse duration, etc.

Lasers can also be categorized by their wavelength or color of emitted light. Common light spectrum includes ultraviolet (UV), visible, and infrared (IR). Examples are Blue lasers that emit visible blue light, and IR lasers like CO2 and fiber lasers.

Therefore, the gain medium category and wavelength category are not mutually exclusive concepts, which means, for example, a CO2 laser can also be referred to an Infrared Laser depending on your method of categorization.

On the other hand, a single gain medium can sometimes produce different wavelengths- for example, some solid-state lasers can emit red, green or blue. Again, these categories overlap - an IR diode laser is both IR as well as solid-state based on its gain medium.

(Laser types and wavelength spectrum source: Wiki)

1.3 The Diode laser

Diode lasers, also known as semiconductor lasers, are a type of laser that utilizes semiconductor materials to generate coherent light. These lasers have become increasingly popular due to their compact size, efficiency, and versatility in various applications.

At the core of a diode laser is a p-n junction, which is formed by joining a p-type semiconductor (with an excess of positive charge carriers called holes) and an n-type semiconductor (with an excess of negative charge carriers called electrons). When a voltage is applied across the p-n junction, the electrons and holes are driven towards each other, and they recombine at the junction. This recombination process releases energy in the form of photons, which is the light emitted by the diode laser.

The wavelength of the emitted light depends on the semiconductor material used and the energy bandgap between the conduction and valence bands in the material. Common materials used in diode lasers include gallium arsenide (GaAs), indium gallium arsenide (InGaAs), and gallium nitride (GaN), each producing different wavelengths of light.

To achieve coherent light emission, diode lasers employ an optical cavity, which consists of two parallel mirrors or reflective surfaces. The light generated by the p-n junction bounces back and forth between these mirrors, causing the photons to interact with the semiconductor material and stimulate the emission of more photons. This process, known as stimulated emission, results in a coherent and monochromatic light output.

(A diagram of an acting laser diode. Source: TutorCIrcle)

Diode lasers can produce a wide range of wavelengths depending on the semiconductor materials used in their construction. Here are some common wavelengths and the corresponding materials used in diode lasers:

1.4 The CO2 laser

CO2 lasers, also known as gas lasers, are gas lasers that produce infrared light with a wavelength of 10600 nm. They are one of the most powerful and efficient continuous wave lasers, and are used extensively for industrial cutting, welding and engraving applications.

In a CO2 laser, the gain medium is a mixture of gases including carbon dioxide, nitrogen and helium. When excited by an electric discharge or radio frequency radiation, molecules of CO2 release photons with a wavelength characteristic of carbon dioxide's molecular resonance. These photons then stimulate the emission of more photons of the same wavelength. The emitted photons bounce back and forth between the mirrors of the laser cavity, leading to amplification of the infrared light.

Two mirrors or reflective surfaces are used to create an optical cavity for the photons, which are placed at either end of the gas-filled tube. One mirror is fully reflective, while the other is partially reflective, allowing some light to pass through. The light generated by the stimulated emission bounces back and forth between these mirrors, amplifying the light through a process called optical feedback. This results in a highly focused, monochromatic, and coherent beam of infrared light.

(The mechanism of CO2 laser engraver. Source: Snap Maker)

1.5 The Fiber Laser

Fiber lasers represent a unique category of lasers, characterized by their use of optical fiber as the active medium. Renowned for their exceptional beam quality, efficiency, and compact design, fiber lasers have become increasingly popular in various industries, particularly for material processing and telecommunications.

The mechanism of a fiber laser is an optical fiber that has been doped with rare-earth elements, such as erbium, ytterbium, or neodymium. These dopants serve as the active medium, enabling the amplification of light within the fiber. To initiate the lasing process, an external pump source, typically a diode laser, is used to inject energy into the doped fiber.

This energy excites the dopant ions, causing them to emit photons through a process called spontaneous emission. These photons then travel along the fiber, interacting with other excited ions and triggering the stimulated emission. This process results in the amplification of light within the fiber, ultimately producing a coherent and monochromatic laser beam.

One of the key features of fiber lasers is their inherent waveguide structure, which is formed by the optical fiber itself. This waveguide confines the light within the fiber core, ensuring that it maintains a consistent path and direction. This confinement leads to exceptional beam quality and stability, as well as a high degree of spatial coherence.

(Source: Catherine Wandera from the book “Fiber Lasers in Material Processing”)

1.6 The Blue light Laser

As we mentioned before, the lasers with the color names are not mutually exclusive concepts with gain medium lasers. Any lasers, no matter its gain medium, which can produce light in the blue region of the visible spectrum, can be referred to blue lasers, with wavelengths of 473 nm and 445 nm being most common. Blue lasers generate an intense and vibrant blue beam that appears prominent to the human eye. They are widely used in applications where a highly visible laser beam is needed like laser projection, biomedical applications, laser lighting displays and material processing.

(445nm - 450nm Blue Laser (middle) Source: Wikipedia)

Unlike infrared lasers like CO2 and fiber lasers that use rare-earth dopants, blue lasers require more complex gain medium and optical pumping to achieve visible blue emission. The most common blue laser is the diode-pumped solid-state or DPSS laser. It uses a semiconductor diode laser to optically pump a crystalline gain medium doped with ions like triply ionized neodymium (Nd3+) that can emit blue light. Popular mediums include yttrium lithium fluoride (YLiF4) and yttrium aluminum garnet (YAG).

The pumping diode laser is absorbed by dopant ions in the crystal, which elevates them to an excited state. The ions release their energy as blue photons when they decay back to the ground state. The gain medium amplifies the blue light through stimulated emission, while the optical cavity directs the emitted photons into a strong, monochromatic blue laser beam.

Blue DPSS lasers can achieve up to 50 milliwatts continuous wave output power using a single gain medium. Higher powers of up to 1 watt or more can be obtained by using multiple crystals or fibers in the same optical cavity. While compact and relatively economical, DPSS blue lasers require complex optics and electronics to function and still have limited output power compared to other laser types.

Apart from DPSS laser which requires complex gain medium, the LaserPecker LP2 also provides a 5-watt, 450nm blue light laser with an ultra-fine 2K resolution, a 600mm/s max engraving speed, and suitable for numerous materials such as paper, wood, bamboo, leather, food, acrylic, colored glass, ceramics, bamboo, stone, etc. It is the most compact and user-friendly machine for beginners.

Click: LaserPecker 3 - Metal & Plastic Handheld Laser Engraver – laserpecker.net

Which laser should choose?

In order to better answer this question, it is better to consider different factors along with your specific requirements.

For the convenience of our discussion, we will no longer focus on specific laser types based on their wavelengths, such as blue or infrared lasers. Instead, we will categorize lasers based on their gain mediums: Diode, CO2, and Fiber Lasers. To provide a better understanding, we will mention the wavelength associated with each laser, indicating the color it belongs to.

2.1 Wavelength and suitable materials

Different wavelengths of each type of laser determine what kinds of materials are suitable to be processed.

Diode lasers emit a range of wavelengths from the visible to infrared spectrum, allowing them to be used on various materials. Near infrared diode lasers at 808 nm and 940 nm are well-suited for engraving and cutting materials such as plastics, textiles and thin metals like stainless steel or aluminum. Blue diode lasers at 445 nm can be used for high-resolution engraving for many materials like opaque acrylic, wood, plastics, fabrics, leather, etc. IR diode lasers around 1-1.5 μm target tissues, plastics and composites in medical and industrial applications.

However, when engraving and cutting on transparent materials using visible diode laser (such as the blue laser), the laser beam would pass through the material without causing any significant effect on the surface of the workpiece. A commonly used solution is to cover the material using engraving or marking tapes.

CO2 lasers emit light in the far infrared at 10.6 μm, delivering high power densities suitable for cutting and engraving most non-metallic materials like acrylic, wood, ceramics, glass and silicon. The 10.6 μm wavelength is also highly absorbed by many thick, industrial metals like aluminum, mild steel and stainless steel. CO2 lasers can thus cut through materials up to 1 inch thick or more. However, the far IR light cannot be used on some metal alloys with poor infrared absorption like copper or brass.

Fiber lasers emit in the near infrared range from around 1.0 to 1.1 μm, which can be used to engrave and cut most metals including steel, aluminum, stainless steel and nickel alloys. The NIR wavelength has high absorption by most metals, allowing for fast, high-power processing of sheets up to a few centimeters thick.

However, fiber lasers typically cannot cut non-metals like wood, acrylic or silicon that are processed efficiently by CO2 lasers. Some plastics and composites also have poor absorption at the fiber laser wavelength, though their power can still be enough to enable surface engraving applications.

2.2 Power range and wall plug efficiency

Diode lasers tend to be compact and electrically efficient. They have a 30-60% efficiency in converting electrical input power to laser output power. The rate of converting electrical energy into laser energy is also called wall plug efficiency. The higher the wall-plug efficiency, the greater the ability of a laser to cut or engrave a material with less electricity consumption.

This high efficiency and low cost have enabled many mass-market applications of diode lasers. However, different wavelengths of diode laser could provide different powers. The maximum power of most diode lasers for engraving is typically limited to tens of watts. Therefore, for industrial level use, a teradiode technique is introduced that combines the output of various diodes to form a single laser beam with a high-power output of up to 8kW. This kind of laser is also called Direct Diode Laser (DDL).

CO2 lasers can achieve very high-power levels of up to 100 kilowatts or more continuous waves, as well as a wall plug efficiency of 10-15%, meaning the CO2 has larger electricity consumption than the diode laser. This makes them suitable for heavy-duty industrial uses such as cutting thick metal sheets, engraving and welding. The laser beam can also be focused to a very small spot size, enabling precision applications.

Fiber lasers can achieve a very wide range of output powers, from below 1 watt up to 100 kilowatts or more. Typical fiber lasers can achieve over 30% wall plug efficiency, with high power single-mode fiber lasers reaching up to 50-60% efficiency or higher. This means they require less energy to operate while generating the same laser power.

2.3 Cutting Speed and thickness

The power of a laser determines the cutting speed and thickness

Diode lasers typically have the lowest cutting speeds around 8 mm/second for a few millimeters thickness of materials like plastics, leather and thin metals. Higher power diode lasers of 1 kW or more can reach up to 50 mm/second cutting speed for stainless steel up to 6mm thick and aluminum up to 8mm, but with lower quality than fiber or CO2 lasers.

CO2 lasers can achieve higher cutting speeds up to around 83 mm/second for stainless steel 12mm thick and 125mm aluminum. CO2 lasers produce high power densities for fast cutting of wood, plastics, and other non-metals as well as thick metals with laser powers of 3kW and above. However, CO2 lasers have lower beam quality so cannot produce the fine, precise cuts possible with fiber lasers.

Fiber lasers provide the highest cutting speeds up to 416 mm/second for stainless steel over 25mm and aluminum over 30mm. Their high precision and narrow cut kerf enable high-speed cutting of most metal alloys with little dross or wasted material. Fiber lasers are the preferred choice where high throughput and part precision are most important.

2.4 Maintenace and life span

Diode lasers generally have the lowest maintenance requirements and longest lifespan of the three lasers. Diode lasers are based on semiconductor components that can operate for up to 100,000 hours without replacement. They do not require any consumable gases. Diode laser maintenance is typically limited to external cooling components. Their compact, solid-state nature also makes diode lasers highly reliable for operating in rough conditions.

CO2 lasers have higher maintenance needs due to their use of laser gases, optics and mirrors that require periodic replenishment and replacement. CO2 lasers typically need new gases every 1-2 years and mirror replacement every 3-5 years for their multi-kilowatt systems. Laser tube and power supply replacement may also be needed after some 10,000-30,000 operating hours depending on usage. Therefore, while CO2 lasers are a mature, cost-effective technology, their higher maintenance results in more downtime and higher operating costs versus fibers or diodes.

Fiber lasers also have gas-free, solid-state designs but with mechanical components like laser diodes and beam delivery fibers that require periodic replacement. Fiber laser diode and pump module lifetimes are typically 10,000 to over 100,000 hours depending on power and usage. Air-cooled fibers last 5-10 years before replacement, while water-cooled fibers used in the highest power systems may need replacement every 1-3 years. Fiber laser maintenance also requires occasional lens, mirror and other optical component replacement. Therefore, fiber lasers have higher initial costs but lower long-term maintenance than CO2 lasers, and a longer potential lifespan than either CO2 or visible gas lasers.

Conclusion

In conclusion, Diode, CO2, Fiber, Blue and Infrared Lasers could be not categorized into 2 different groups depending on their gain medium or their wavelength. The wavelength and gain medium are not mutually exclusive concepts, a laser could be both blue and CO2 laser.

Different gain mediums provide different ways of laser creations, which also offer various features such as suitable materials, power range, wall-plug efficiency, speed, cutting thickness and maintenance methods.