Analysis of the Differences in Absorption Rates of Laser Wavelengths by Different Materials

In laser processing, whether laser energy can effectively act on a material depends on the material’s ability to absorb a specific laser wavelength. Different materials exhibit significant differences in absorption rates at different wavelengths, and these differences directly affect the efficiency, stability, and processing quality of laser cutting, welding, marking, and cleaning. Understanding material–wavelength absorption characteristics is the foundation for laser process selection and parameter optimization.

I. Basic Relationship Between Laser Wavelength and Absorption Rate

Laser absorption rate refers to the proportion of incident laser energy absorbed by a material surface. It is influenced by the following factors:

Laser wavelength

Electronic structure and lattice characteristics of the material

Surface condition (roughness, oxide layer, coatings)

Angle of incidence and polarization state

In most cases, a material’s absorption rate is not a fixed value but varies significantly with wavelength. Therefore, the same material can exhibit markedly different processing results when exposed to different types of lasers (such as CO₂, fiber, green, or ultraviolet lasers).

II. Absorption Characteristics of Different Laser Wavelengths for Metal Materials
1. Ferrous Metals (Carbon Steel, Stainless Steel)

Ferrous metals exhibit relatively stable absorption in the near-infrared band (around 1.06 μm):

High absorption for 1064 nm fiber lasers

Good energy coupling with 10.6 μm CO₂ lasers

Further increased absorption after surface oxidation or roughening

As a result, fiber lasers and CO₂ lasers are widely used for cutting and welding steel materials.

2. Highly Reflective Metals (Aluminum, Copper, Gold, Silver)

Highly reflective metals have low absorption in the infrared band:

Low initial absorption for 1064 nm lasers, with strong reflection

Significantly higher absorption at shorter wavelengths (green 532 nm, blue 450 nm)

Absorption increases dynamically as temperature rises

This is the main reason why green and blue lasers have been rapidly adopted in copper welding and precision aluminum processing in recent years.

III. Wavelength Absorption Characteristics of Non-Metal Materials
1. Plastics and Polymer Materials

The absorption characteristics of plastics are closely related to their molecular structure:

Most plastics are transparent or weakly absorbing in the near-infrared range

High absorption in the mid- to far-infrared band (10.6 μm)

Absorption characteristics can be significantly altered by adding pigments or absorbers

Therefore, CO₂ lasers are widely used for plastic cutting, marking, and thin-film processing.

2. Wood, Paper, and Organic Materials

Organic materials generally exhibit high absorption for infrared lasers:

High absorption efficiency for CO₂ lasers

Prone to thermal decomposition, carbonization, and vaporization

Relatively large heat-affected zones during processing

These materials are suitable for low-power continuous or pulsed infrared laser processing.

IV. Ceramics, Glass, and Transparent Materials

Transparent or semi-transparent materials show strong wavelength dependence in absorption:

Low absorption and high transmittance in the infrared and visible ranges

Significantly increased absorption in the ultraviolet range

Short-wavelength lasers more readily induce multiphoton absorption

As a result, ultraviolet lasers have clear advantages in glass drilling and precision ceramic processing.

V. Influence of Material Surface on Absorption Rate

In addition to intrinsic material properties, surface condition also affects absorption efficiency:

Rough surfaces absorb laser energy more easily than mirror-like surfaces

Oxide layers and coatings can reduce reflectivity

Surface contaminants can increase initial absorption in certain processes

In the processing of highly reflective materials, surface pretreatment is often used to improve laser energy coupling.

VI. Impact of Absorption Differences on Laser Processing

Differences in material absorption rates at various laser wavelengths directly affect:

Selection of laser type

Power and energy density settings

Processing speed and stability

Size of the heat-affected zone and forming quality

By properly matching the material with an appropriate laser wavelength, it is possible to reduce energy consumption while improving processing quality and equipment safety.

Significant differences exist in the absorption rates of different materials at various laser wavelengths. These differences are determined by the material’s electronic structure, molecular vibration characteristics, and surface condition. In laser processing applications, selecting a laser wavelength that matches the material’s absorption characteristics is key to achieving high efficiency and high-quality results. With the development of short-wavelength laser technologies, processing capabilities for highly reflective and transparent materials continue to improve.