Why does processing high-reflective materials burn the laser?

When processing highly reflective materials (such as aluminum, copper, gold, etc.), the main reasons for laser burnout are as follows:

1. Low absorption leads to increased reflected energy

The surface of highly reflective materials has a low absorption rate for lasers, especially within the common laser wavelength range. For example, metals such as aluminum and copper have a high reflectivity for most wavelengths of lasers (especially red lasers), usually reaching more than 90%. In this way, when the laser hits the surface of these materials, most of the energy is not absorbed by the material, but is reflected back to the laser's optical system.

The reflected energy can affect the laser in the following ways:

Reflection back to the laser source: The reflected beam may return to the laser source or the laser's output lens. This reflected energy acts directly on the laser, increasing its internal temperature, which may cause the laser to overheat or even damage.

Reflection to optical components: The reflected laser energy may also return to optical components such as focusing lenses, lenses or mirrors, which will cause the temperature of the optical components to rise rapidly, and in severe cases may cause them to deform, burn or cause coating damage.

2. Focusing effect exacerbates reflection problems

The laser's focused spot is usually very small and has a high energy density. During processing, the laser beam is accurately focused onto the workpiece surface, producing a high-intensity thermal effect. For highly reflective materials, the amount of light reflected back to the laser by the focused laser beam increases significantly, especially during high-power laser processing, where the reflected energy exacerbates this situation. Even the reflected light may cause damage to the laser's internal components due to excessive energy or improper return path.

3. Damage to optical components

The optical system of the laser (such as lens, reflector, lens) is usually designed to receive only part of the laser energy from the target surface or absorbed. When a large amount of laser energy is reflected back to the optical system by highly reflective materials, the optical components cannot withstand this additional reflected energy, which is prone to:

Lens burn: Optical components such as lenses and reflectors may burn, lose coatings, or even develop thermal cracks due to excessive temperatures.

Deformation of optical components: High temperature may cause deformation of lenses and reflectors, affecting the beam quality, resulting in unstable laser output or even malfunction.

4. The laser working stability is reduced

Long-term reflected laser energy will affect the cooling system inside the laser, resulting in reduced cooling efficiency, which in turn causes the laser to overheat. The temperature control system inside the laser usually relies on a stable heat dissipation mechanism, but continuous reflected lasers will keep the temperature at a high level, causing the temperature control system to be unable to effectively dissipate heat, and then damage or burn out the laser components (such as laser sources, amplifiers, crystals, etc.).

5. Risks of high-power laser processing

In high-power laser processing, especially high-power lasers (such as CO2 lasers, fiber lasers, etc.), the energy output by the laser is very high. When the laser beam contacts a highly reflective material, the reflected energy is relatively large. The high reflected energy not only puts a large heat load on the laser source itself, but may also cause damage to optical components. The laser design does not have the ability to cope with large reflection reflux, so equipment failure is particularly prone to occur at high power.

Solution

To solve this problem, laser manufacturers usually take the following measures to reduce the burning caused by reflection:

Use short wavelength lasers: Blue lasers (such as 450 nm wavelength) have a higher absorption rate on highly reflective materials, which can effectively reduce the reflected energy.

Adjust beam parameters: Reduce reflected energy by adjusting laser power, pulse frequency and focusing method.

Use reflection protection devices: such as reflector protection, reflective light guides, anti-reflection coatings, etc. to reduce the damage of reflected light to lasers and optical components.

In summary, when processing highly reflective materials, the laser and optical system are at risk of overheating and damage due to excessive reflected energy. After understanding these issues, it is crucial to choose the appropriate laser type and processing parameters.