Laser Classification

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

Laser Classification

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.

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