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Direct Diode Lasers Explained: Advantages, Limitations

Direct Diode Lasers Explained: Advantages, Limitations

Direct Diode Lasers Explained: Advantages, Limitations

Laser-cutting technology has gone through rapid development and is one of the most commonly used techniques for manufacturing.

The introduction of direct diode lasers has enabled the production of low-cost laser cutters that have comparatively low-power output and are suitable for DIY applications.

Direct diode lasers are a type of laser where the output of a diode laser module is directly used for the application. This eliminates the need for a complex beam delivery system, resulting in compact equipment, making it possible to combine multiple diode lasers to produce a powerful laser beam.

This article discusses direct diode lasers in detail by shedding some light on their recent developments, along with their advantages and limitations. 

In the end, I've also compared direct diode lasers with fiber and CO2 lasers.

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What are Direct Diode Lasers (DDL)?

Direct diode laser
Direct diode laser

Direct diode lasers are a type of laser that use semi-conductor diodes to generate a concentrated beam of light and use it directly on the workpiece to perform laser ablation.

The absence of a gain medium and beam delivery system reduces the power consumption of direct diode lasers, making them one of the most efficient lasers.

However, high-powered diode lasers require basic components like a dispersion medium, and an output coupler to combine the beams and deliver them onto the required surface through a focusing lens. 

The output coupler converges the beams from multiple input diode lasers (laser array) to produce a high-energy laser beam.

Diode lasers are available in different types with different wavelength configurations. As a result, a beam homogenizer is required to reduce the variations between individual beams.

After combining the laser output from different diode sources, the laser beam is passed through a focusing lens to converge it on the workpiece.

Material Capability of Direct Diode Lasers (DDL)

Direct diode lasers have a broad range of operational wavelengths ranging from 550nm to 950nm.

This makes them suitable for cutting and engraving almost any laserable material.

These lasers can be used to cut and engrave non-metals like paper, wood, leather, foam, fabric, plastics, acrylics, etc.

Apart from that, they can also be used to cut and engrave metals such as aluminum, brass, steel, etc.

However, these lasers are generally available in low-power options, making them ideal for laser cutting very thin workpieces.

Industrial Direct Diode Laser Cutters

Multi-laser beam combining for high-power diode lasers
Multi-laser beam combining for high-power diode lasers

Diode lasers have a simple construction which makes them compact in size.

As a result, the laser output of multiple modules can be combined together by stacking them on top of each other and using suitable laser optics.

This technique has shown effective results and is also used in diode laser cutters for home, such as xTool D1 pro, which uses four diode modules with 5W power output each to provide a total power output of 20W.

Advancements in laser diode technology have improved the beam quality and laser output power by implementing various coupling methods like side-by-side beam coupling.

Using multiple diodes as the input to the laser diode module increases the output power to reach power levels of up to 8kW, which was not previously possible. 

This has made it possible for direct diode lasers to be used for laser cutting different materials, including sheet metals.

However, there is still scope for improvement in the laser beam quality. This has to be done by modifying the beam geometry by either using more precise optics or laser diodes with improved beam quality.  

The table below gives some practical data on the cutting speeds of different lasers with the same power rating on stainless steel and aluminum. 

Material2 kW Direct Diode Laser 2kW Fiber Laser 2kW CO2 Laser
0.4” stainless steel4.33 ipm11 ipm2.95 ipm
0.4” aluminum5 ipm3 ipm11 ipm
Differentiating the laser processing capabilities of diode laser against fiber laser and CO2 laser

Applications of Direct Diode Lasers

Machining applications of direct diode lasers
Machining applications of direct diode lasers

Direct diode lasers are more efficient than conventional fiber lasers due to the absence of a gain medium.

Using an output coupler converges the energies from the individual diode lasers, increasing the beam spot energy. 

This allows the direct diode laser to cut materials almost 15% quicker than its traditional counterparts, such as fiber and CO2 lasers.

In the case of aluminum, the cutting speed is almost 30% faster if you use a direct diode laser.

Their compact size and low cost make them ideal for portable laser cutters and budget-friendly laser cutters.

Apart from laser cutting, direct diode lasers are also used for different packaging and heat treatment applications.

When packaging food, two important processes directly affect the quality and shelf-life of the food: shrink wrapping and seam heating. 

Direct diode lasers allow controlled heat with precise temperature control, providing the ability to improve the quality while keeping the packaging intact.

In semiconductor manufacturing industries, it is often required to heat the substrate material to induce thermal annealing or dopant ion activation.

Direct diode lasers offer the needed control, brightness, beam spot size, and power for such processes.  

Apart from that, certain applications require mounting laser modules on mobile devices for heat treatment and cladding.

Since direct diode lasers have no gain medium, they are more compact and suitable for such applications. 

Direct diode lasers are also prevalent in medical applications such as effective hair removal without damaging the dermis and causing minimal pain or discomfort to the patient. 

Advantages of Direct Diode Lasers

Portable direct diode laser engraver
Compact size portable direct diode laser engraver

Direct diode lasers don’t have any laser gain medium, and the electrical energy is directly converted into light energy that is converged using an output coupler and used on the workpiece.

This makes them compact and, comparatively, more economical than fiber and CO2 lasers. 

Diode lasers are available with a wide range of wavelengths from 450nm to 950nm, making them suitable for cutting and engraving almost any material.

Furthermore, their low initial cost makes them ideal for low-cost laser cutters, making laser cutting accessible for almost every DIY enthusiast.

However, you can increase the output power by using multiple diode laser modules. As a result, modern direct diode lasers can have laser power in the range of a few kilowatts, suitable for industrial applications.

These high-powered direct diode lasers can cut different materials at 15–30% faster speeds than other lasers.

Limitations of Direct Diode Lasers

The beam spot size of a direct diode laser is rectangular and not circular. This might make it unsuitable for some cutting applications where a circular beam spot is required.

Direct diode lasers are more prone to beam divergence compared to other lasers. Hence, poor optics and improper output coupler can hamper the beam spot efficiency.

They can pose some complications during medical applications because they have a poor absorption rate in hard tissues and take longer to cut through chunks of tissue than electrosurgery. 

Direct Diode Lasers vs Other Lasers 

Direct Diode Lasers vs Fiber Lasers

ParameterDirect Diode LaserFiber Lasers
Wavelength450-950nm1060nm
Materials Metals and non-metalsMostly metals 
Power 1.5W-8kW10W-15kW
MaintenanceLowModerate 
Difference between direct diode laser and fiber laser

Direct diode lasers and fiber lasers operate in different wavelength ranges. Direct diode lasers operate in the range of 450-950nm, while fiber lasers operate at a higher wavelength of about 1060nm.

This difference in wavelength significantly affects the materials that they can process. 

Direct diode lasers can work on different metals and non-metals like mild steel, aluminum, brass, wood, glass, textile, etc.

Due to their higher operational wavelength, fiber lasers are best suited to laser cutting metals and engraving some types of plastics.

For example, if a fiber laser is used on wood, it will cause hotspots on the surface of the workpiece and can cause a fire. 

However, both direct diode and fiber lasers can’t work on clear glass as the beams pass through the material without getting absorbed. 

Direct diode lasers are available in power levels from 1.5W to 8kW. The absence of a laser medium and a simple design make it compact.

As a result, direct diode lasers are also available in small modules that can even fit in the palm of your hand.

Fiber lasers are also available over a wide range of power levels from 10W to 15kW. 

Due to the availability of higher-power fiber lasers, they can cut through thicker materials than direct diode lasers. However, the edge finish provided by direct diode lasers is superior to that of fiber lasers. 

Direct diode lasers have lower start-up and operational costs when compared to fiber lasers. This, along with the higher material processibility, makes them a very good choice for DIY applications. 

The table below summarizes the material processing capability of direct diode lasers and fiber lasers.

MaterialDirect Diode lasersFiber Lasers
Mild Steel
Stainless Steel
Aluminum
Copper
Brass
Acrylic
Plastics
Wood
Textile
Clear glass
Stone
Material capabilities of diode laser and fiber laser

Direct Diode Lasers vs CO2 Lasers

ParameterDirect Diode LaserCO2 Laser
Wavelength450-950nm10600nm
MaterialsMost metals and non-metalsNon-metals and few metals
Start-up costsModerateModerate
Operational costs and maintenance Moderate to lowVery high
Difference between direct diode laser and CO2 laser

CO2 lasers work at a much higher wavelength of 10600nm, whereas direct diode lasers work in the 450-950nm range. 

This large wavelength of CO2 lasers makes them unsuitable for cutting and engraving almost every non-metal.

Apart from that, a high-powered CO2 laser can also be used to laser-cut metals like aluminum but cannot be used to engrave them.

On the other hand, direct diode lasers can be used to cut and engrave metals as well as non-metals. This is due to their comparatively lower operational wavelength range.

Although entry-level diode lasers like the Comgrow Z1Atomstack X7, and xTool D1 pro are available at cheaper rates, the high-powered direct diode lasers are relatively new and are not readily available on the market.

Whereas CO2 lasers are available with different power output configurations, ranging from 40W CO2 lasers to 20kW industrial lasers.

As a result, CO2 lasers are comparatively more dominant in the industrial sector.

However, diode lasers are comparatively more economical because CO2 lasers require high electricity consumption to generate the laser in the laser tube.

Moreover, CO2 lasers need regular maintenance involving mirror and lens cleaning, bellow checks, gas replacement, and sometimes even replacing the laser tube. 

In contrast, direct diode lasers have simple and robust construction that eliminates the need for regular maintenance, except for cleaning the lens.

The tables below summarize the differences between direct diode lasers and CO2 lasers, along with their material processing capabilities. 

MaterialDirect diode laserCO2
Mild Steel
Stainless Steel
Aluminum
Copper
Brass
Acrylic
Plastics
Wood
Textile
Clear glass
Stone
Material capabilities of diode laser and CO2 laser

Frequently Asked Questions (FAQ)

What are some of the coupling methods used to improve beam quality in direct diode lasers?

Some of the coupling methods used to improve beam quality in direct diode lasers are side-by-side beam coupling & polarization and wavelength coupling. Side-by-side beam coupling is used for traditional diode laser arrays and needs more precisely designed optics. On the other hand, polarization and wavelength coupling require better coatings on the optics that are used. 

What are the basic differences between a direct diode laser and a UV laser?

UV lasers work in a wavelength range of 355nm, and direct diode lasers work in 550-950nm range. UV lasers are mostly used for laser marking applications as they are unavailable at higher power levels. This is why they are also called blue or cold lasers. Direct diode lasers can be used for marking, engraving, and cutting as they are available in different power options, from 10W to 8kW.  

What are the applications of CNC machines?

CNC machines are used for various applications in material prototyping and 3D modeling. The industrial applications of CNC machining involve engraving, deep engraving, and cutting materials. High-end CNC machines can machine parts and attain complex shapes with high repeatability and accuracy. CNC machines can be highly automated, which greatly reduces the cycle time of parts and the need for skilled labor, thereby increasing the production rate and decreasing manufacturing costs. 

About John

Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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