Laser Classification

There are two primary types of lasers utilized for welding, CO₂ lasers and Nd:YAG lasers.

Both CO₂ and Nd:YAG lasers are invisible to the naked eye.

The light beam generated by the Nd:YAG laser is primarily near-infrared light with a wavelength of 1.06 μm.

This wavelength has a high light absorption rate for heat conductors and a reflectivity of 20-30% for most metals.

The light beam can be focused to a diameter of 0.25 mm with a standard light microscope.

On the other hand, the light beam of the CO₂ laser is far-infrared with a wavelength of 10.6 μm.

Most metals have a reflectivity of 80-90% for this light, and a special light microscope should be used to focus the beam to a diameter of 0.75 – 0.1 mm.

The power of Nd:YAG lasers can typically reach 4,000 – 6,000 W, with some reaching up to 10,000 W.

CO₂ laser power, on the other hand, can easily reach 20,000 W or even higher.

The high reflectivity of metals is addressed by the high-power CO₂ laser through the “small hole effect”.

When the material surface is irradiated by the laser, a small hole forms as the surface melts. This vapor-filled hole acts as a black body, absorbing almost all of the incident light’s energy.

The temperature inside the cavity reaches about 25,000 K.

Within a few microseconds, the reflectivity drops significantly.

While the focus of CO₂ laser development has primarily been on improving equipment, the emphasis has shifted to improving beam quality and focusing performance rather than increasing maximum output power.

Additionally, when using a CO₂ laser with a power of 10 kW or more for welding, the use of argon gas often creates a strong plasma, leading to shallower penetration.

As a result, in high-power CO₂ laser welding, helium gas, which does not generate plasma, is often used as a shielding gas.

The application of diode laser combinations for exciting high-power Nd:YAG crystals is a significant development issue that will greatly enhance laser beam quality and increase laser processing efficiency.

The direct diode array is used to excite lasers with a near-infrared output wavelength, with an average power of 1 kW and a photoelectric conversion efficiency of nearly 50%.

The diode also has a longer lifespan of 10,000 hours, reducing the maintenance costs of laser equipment.