Differences between fiber and CO2 laser lenses

Introduction: The Heart of Your Laser System

At the core of every high-precision laser cutting and welding machine lies a critical component: the focusing lens assembly. This optical system is responsible for taking the powerful laser beam and concentrating its energy into an incredibly small, intense spot, which is what allows the laser to cut through metal or weld it with such precision. However, not all lasers are the same, and consequently, neither are their lens assemblies. For fiber laser lens, different laser cutting head manufacturers have the different design for the optical path and structure, even they might have the same diameter and focal length. As for the CO2 focusing lens, the shape, diameter, edge thickness, focal length are the key parameters for which all users need to know before purchase.

The Fundamental Difference: It All Starts with Wavelength

The single most important factor distinguishing these two lenses is the wavelength of laser light they are designed to work with. Wavelength, measured in microns (μm) or nanometers (nm), determines how light interacts with matter, including the lens material itself.

• CO2 Lasers: These lasers operate at a long wavelength of 10.6 micrometers (μm). This is in the mid-infrared spectrum, which is invisible to the human eye.
• Fiber Lasers: In contrast, fiber lasers produce light at a much shorter wavelength, typically around 1.07 micrometers (μm) or 1064 nanometers (nm). This is in the near-infrared spectrum.

Why does this matter? Imagine trying to use a glass window to focus the heat from a campfire. The glass might block the heat (long-wave infrared) while letting visible light through. Similarly, materials that are perfectly transparent to one wavelength of light can be completely opaque or absorbing to another. This is the primary reason why a fiber laser lens assembly cannot be used in a CO2 laser system, and vice versa.

Lens Material: The Key to Transparency and Power Handling

The different wavelengths directly dictate the materials from which the individual optical elements within the lens assembly must be manufactured. This choice impacts cost, durability, and performance, especially under high-power conditions.

• CO2 Laser Lenses: The gold-standard material for the optical elements in a CO2 lens assembly is Zinc Selenide (ZnSe). ZnSe has an exceptionally low absorption rate for the 10.6μm wavelength, allowing the laser energy to pass through with minimal loss and heat generation. Other materials like Germanium (Ge) and Gallium Arsenide (GaAs) are also used for specific high-power or specialized applications. These materials are often more expensive and can be sensitive to thermal shock.

Fiber Laser Lenses: The material of choice for the optical elements in a standard fiber laser lens assembly is Fused Silica or synthetic quartz. Fused Silica offers superb transparency to the 1μm wavelength, high thermal stability, and excellent resistance to thermal lensing—a phenomenon where the lens heats up and changes shape, defocusing the beam. It is also very hard and resistant to contamination, making it durable for industrial environments.

Optical Design: Lens Assembly vs. Optical Elements

Understanding the optical design requires distinguishing between the complete "lens assembly" and the individual "optical elements" inside it. A focusing lens is a system, and its implementation is not bound to a single type of optical element.

CO2 Laser Optics: A CO2 laser focusing assembly can utilize both transmissive (using lenses) and reflective (using mirrors) designs. While ZnSe lenses are common, at very high power levels (e.g., multiple kilowatts), reflective focusing mirrors become preferred. These are often parabolic mirrors made from copper or molybdenum. This is a prime example where a "CO2 focusing lens assembly" does not necessarily contain a transmissive lens element at all; its core component could be a reflective mirror.

Fiber Laser Optics: A modern fiber laser cutting head is a complex optical system. This lens assembly typically contains multiple elements: a collimating lens group, a focusing lens group, and a protective window. The core focusing element within this assembly is most commonly made from Fused Silica due to its excellent overall properties. However, it is crucial to understand that this element can be a single lens, a doublet (two lenses cemented together), or even an aspherical lens, depending on the required performance. Therefore, the relationship between a "fiber laser lens assembly" and a specific "lens element" is not fixed; it is a tailored solution.

Application Focus: Why the Right Lens Defines Your Results

The wavelength difference doesn't just affect the lens; it dictates what materials the laser can process efficiently.

• CO2 Lasers with ZnSe Lenses: The 10.6μm wavelength is excellently absorbed by non-metallic materials. This makes CO2 lasers, paired with the correct lens assembly, the superior choice for cutting and engraving wood, acrylic, plastics, textiles, and ceramics.
• Fiber Lasers with Fused Silica Lenses: The 1μm wavelength is absorbed much more efficiently by metals. This makes the fiber laser lens assembly the heart of modern metal fabrication. It is the key component enabling the cutting, welding, and marking of steel, stainless steel, aluminum, brass, and copper with unparalleled speed and energy efficiency.

What Are the Differences on Maintenance for CO2 Optics and Fiber Optics

Owing to the unique properties of 1064nm near-infrared lasers, their fundamental beam quality, and compact design, fiber laser cutting has demonstrated significant advantages in processing efficiency, precision, and cost-effectiveness. Particularly suited for metal fabrication applications, fiber laser systems have been rapidly gaining market share from CO2 laser cutting machines in recent years. Compared to CO2 lasers, fiber lasers require lower maintenance costs for their core optical components and are easier to replace. Manufacturers continuously optimize cutting head designs, enabling users to replace parts promptly without damaging internal components. For instance, the focusing lens drawer and collimating lens drawer allow users to perform replacements in a clean environment without needing professional assistance. However, due to the complex internal structure of the CO2 laser, the replacement of all optical components must be carried out by professionals on site, which is not cheap.