In the optical system of a laser marking machine, the field lens is used to focus the laser beam output by the galvanometer system onto the work surface and ensure the stability of the spot size within the scanning range. The material and parameters of the field lens directly affect the laser transmission efficiency, imaging quality, and processing effect. Common field lenses include ordinary field lenses and quartz field lenses, which differ in optical performance and application requirements.
1. Material differences
Ordinary field lenses are usually made of optical glass. Quartz field lenses are made of fused quartz. Fused quartz has a lower coefficient of thermal expansion, higher thermal resistance and a higher laser damage threshold.
2. Laser transmittance differences
In the 1064 nm band (a commonly used band for fiber lasers) and the 355 nm band (a commonly used band for ultraviolet lasers), the transmittance of fused quartz is higher than that of ordinary optical glass.
A higher transmittance reduces laser energy loss and increases the effective output power of the system. The transmittance of ordinary field lenses decreases more significantly under high power or long-term operation.
3. Differences in Laser Damage Threshold
The laser damage threshold of quartz field lenses is high, enabling them to withstand higher power density and higher energy density laser pulses.
Ordinary glass field lenses are prone to surface ablation, coating detachment or spot drift in high-power or small-spot applications.
4. Differences in Thermal Stability
The thermal expansion coefficient of fused quartz is low, making it less likely to cause changes in focal length due to temperature increase.
Ordinary glass has a large thermal expansion coefficient. In long-term processing or high-temperature environments, its focal length stability is poor, and there may be focus drift, uneven marking depth or line width changes.
5. Image quality differences
The dispersion of the quartz field lens is low, and the quality stability of the focal spot is high. It can obtain a smaller focused spot, which is suitable for high-precision processing.
Ordinary field lenses may encounter edge blurring or uneven energy distribution in high-precision graphics, small fonts, and QR code processing.
6. Differences in Service Life
The quartz field lens has high thermal resistance and a high laser damage threshold, resulting in a long service life. The lifespan of ordinary field lenses is affected by heat, energy load, and the stability of the surface coating. Therefore, their service time is relatively shorter.
7. Cost Variance
The manufacturing cost of quartz field lenses is high, and the optical processing and coating processes have strict requirements. Therefore, their prices are higher than those of ordinary field lenses. Ordinary field lenses have lower costs and are suitable for general power processing scenarios.
8. Differences in application scenarios
I.Quartz field lenses are commonly used for:
High-power fiber laser marking
Ultraviolet laser marking
Precision processing, small spot application
Long-duration continuous processing scenario
II.Ordinary field lenses are commonly used for:
Medium and low power fiber laser equipment
Common metal and plastic marking
Processing tasks with relatively low requirements for the quality of the focal spot
The main differences between ordinary field lenses and quartz field lenses lie in their materials, transmittance, laser damage threshold, thermal stability, spot quality, and cost. Quartz field lenses have superior performance and are suitable for high-power and high-precision applications; while ordinary field lenses are cost-effective and are suitable for general marking requirements.