Scientists develop flat-topped laser beams to overcome Gaussian distribution limitations

The beam emitted by almost all laser systems follows the Angle pattern of Gaussian distribution. The Gaussian irradiance distribution means that irradiance has a smooth peak at the center point and slowly declines toward the edge. In theory, the irradiance level of a Gaussian distribution can never reach zero, which means that the distribution can expand indefinitely. This phenomenon in the laser beam results in a large amount of light energy being wasted. However, for a variety of practical applications, we need a laser beam system that minimizes light energy waste. To solve this problem, flat-topped laser beams have been developed to overcome the limitations of Gaussian distribution and provide a beam distribution with sharp edges and uniform irradiance.

The role of DOE in beam shaping

Since a laser beam naturally does not exhibit a flat-topped beam profile, we need to convert a Gaussian beam to a flat-topped beam using an add-on or a beam shaper. This modification enables the beam profile to be used for a variety of laser applications. Analytical beam shaper and diffuser Beam shapers are the two main types of flat-top laser beam shapers.

A DOE (or diffractive Optical element) is an analytical beam shaper consisting of a single element designed to change the wavefront of a beam. DOE is a computer-generated hologram (CGH) combined with a specific delay topology that exploits the properties of light waves. The structure of the DOE can be designed to perform complex changes to coherent beams, such as laser beams.

Diffractive optical elements (DOE) introduce precise phase transitions for the beam. As the beam propagates, this phase transition produces a smooth, flat-topped irradiance distribution at the focal point. The shape of the profile can be customized on request, such as round, square, rectangular or straight.

Therefore, the main advantage of using such beam shapers is their excellent performance in terms of coherent beams such as TEM00 Gaussian beams with low M2 values. This type of input coherent beam has important applications in the laser material processing industry. In contrast, the use of diffuse elements as beam shapers is common in multi-mode, low-coherence laser beams.

DOE beam shaper Settings

The setup of the beam shaper consists of a laser beam entering the DOE and a focusing lens (such as an F-Theta lens) placed behind the DOE. The aim is to reproduce the far field of DOE in the focal plane. The beam shaper performs best when the through-light aperture of the lens is twice or more that of the DOE and the lens has no aberrations.

Application field

Flat-topped laser beam profiles have important applications in various industries such as semiconductors and microelectronics, where these beam irradiance profiles can be used for tasks such as drilling, copper removal, and contact scribing. The top hat laser beam also has important applications in high-tech manufacturing, green energy industry, especially laser metal processing industry.

Source: Laser Network