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What is the difference between Top-hat beam and Gaussian beam?

Lasers are generally Gaussian beams, that is, the beam intensity presents a Gaussian distribution in space. Such a beam has a very high intermediate intensity and gradually decreases along the Gaussian profile.

In practical applications, not only Gaussian beams are often required, but also laser beams have specific requirements for specific application requirements. For example: in the energy distribution, it has a circular distribution; in the beam shape, it has a square, a circle and other shapes.

The energy distribution of the Gaussian beam is relatively uneven, and the middle energy is too high, which will cause the local temperature to be too high and affect the interaction between the laser and the matter; the energy of the two wings is too low, which reduces the utilization rate. Therefore, in some occasions, it is necessary to shape the Gaussian beam into a flat-top beam with uniform energy distribution to improve the laser processing effect.

The following figures show the characteristics of the Gaussian laser profile and the flat-topped laser profile:

The low-intensity parts on either side of the available central area of ​​the beam are called “wings”, and their intensity is lower than the burning threshold required for laser processing applications. The energy of these two wings is usually wasted, resulting in greatly reduced energy utilization; at the same time, the two wings The energy also damages surrounding areas beyond the target area, expanding the heat-affected zone. On the other hand, the high-intensity part above the burn threshold is called “excess energy”, and these excess energy has the potential to damage the substrate; what is more, the central part of the energy is too concentrated, it is easy to damage the optical device.

Flat-top laser beams use energy more efficiently than Gaussian laser beams. In the Gaussian beam profile, excess energy in the middle above the intensity threshold required by the application and energy in the wings below the threshold requirement are wasted. The flat-top beam profile has no two wings, but has a steeper edge transition, so energy is more efficient and there is less damage to the surrounding area.

As can be seen from the graph above, the energy of a flat-top beam is more clearly contained in a given area than a Gaussian beam. Welding or cutting with a flat top beam will be more accurate and less damage to the surrounding area.

When cutting with a flat-top beam, it produces cleaner cuts and sharper edges.

When welding with a flat-top beam, the welding gap will be smoother than in the case of a Gaussian beam.

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