Introduction

Laser technology has revolutionized numerous industries, and its application in medical device manufacturing is no exception. Among the various types of lasers, infrared picosecond (IR ps) and ultraviolet nanosecond (UV ns) lasers stand out for their unique processing capabilities. This article provides a comprehensive comparison of these two laser types, focusing on their principles, technical parameters, and advantages in marking medical devices, specifically stainless steel surgical instruments.

Laser Processing Principles

1.Long Pulse Lasers–Thermal Processing Mechanism

Long pulse lasers, such as infrared and ultraviolet nanosecond lasers, operate on a thermal processing mechanism. When these lasers irradiate a material, the energy absorbed through Joule heating raises the temperature in the irradiated area, causing it to melt and vaporize, thereby removing material. Despite advancements in process development allowing for crack-free cutting, the intrinsic thermal effects of long pulse lasers can significantly reduce processing precision. Common issues include macroscopic heat-affected zones, cut surface striations, molten layers, and dross at the cut edges.

2.Ultra-Short Pulse Lasers–Cold Processing Mechanism

In contrast, picosecond lasers, with pulse widths in the range of 10^-11 to 10^-12 seconds, operate on a cold processing mechanism. The interaction time of the photons with the material is shorter than the thermal vibration transfer time between the material’s conduction band electrons and lattice. This means there is insufficient time for heat transfer between electrons and the lattice during processing. The material removal occurs through electronic excitation and ionization, reaching a critical threshold that leads to irreversible lattice structure damage without significant heat effects, thus minimizing thermal impact.

Technical Parameters

The following table outlines the technical parameters for different laser types:

Advantages of Infrared Picosecond Lasers

1.Enhanced Corrosion Resistance

Laser marking on stainless steel surgical instruments is a critical application in the medical device industry. These instruments often require markings for identification, such as numbers, letters, QR codes, and company names. Given the harsh environments these instruments are subjected to, the markings must exhibit superior corrosion resistance, passivation, and withstand high-pressure sterilization and boiling.

In corrosion resistance tests comparing different lasers, infrared nanosecond lasers produced large heat-affected zones that damaged the stainless steel passivation layer, leading to rusting in salt spray tests. Although UV nanosecond lasers offer “near-cold ablation,” their thermal ablation mechanism still results in heat-affected zones and subsequent rusting. In contrast, infrared picosecond lasers, due to their cold processing mechanism, do not damage the stainless steel passivation layer, maintaining corrosion resistance comparable to the stainless steel substrate.

2.High Contrast and Durability

Infrared picosecond laser markings on surgical instruments exhibit higher contrast and clarity, visible from various angles with sharp edges. This negates the need for complex passivation stages in the production process, reducing manufacturing costs.

Conclusion

Commercially available infrared picosecond lasers are increasingly being adopted in the market due to their excellent beam quality, stable power and frequency output, and relatively low acquisition, maintenance, and operational costs. Their broad applicability across various materials makes them ideal for precision micromachining. The unique material removal mechanism and minimal thermal effects of infrared picosecond lasers promise expanded application ranges, marking a significant advancement in laser processing technology for medical devices.