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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.
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.