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A beam shaper is an optical element that changes the radiance distribution of an input beam to some predefined alternative distribution. In particular, the most common transformation sought after is to convert the inherent Gaussian radiance distribution of most laser beams to a beam with a Top Hat radiance distribution.
A Gaussian radiance distribution is described by, as the name implies, a Gaussian formula which is of the same form as the Gaussian equation found in statistics for the normal distribution. Thus, a radiance distribution of this sort is described by a smooth maximum at the centre of the beam that then slowly decays towards the edges. For various reasons, this sort of beam shape is not optimal in many applications for laser systems. First of all, the irradiance on the surface being treated is not uniform as the maximum is located at a very small point. Secondly, the beam spreads over a large area and some light leakage, however small, always occurs.
In contrast, a Top Hat beam exhibits a plateau of uniform radiance with well defined, steep, boundaries. Thus, no light creeps outside the predefined boundaries for this plateau.
For the reasons mentioned above, it can be ascertained that a beam shaper is a very useful component that can be included in laser systems for materials processing or medical treatments in order to maximise throughput and power efficiency.
The output of the Top Hat beam shaper is not limited to a Top Hat beam. In fact, a more generic name for the output beam is Flat Top beam. The reason stems from the fact that the shape of the output beam is not limited to a circular or rectangular shape, whose cross profile will resemble a Top Hat, but to any other shape, even groups of isolated areas of constant radiance, as in the case of parallel lines.
Another type of beam shaper is the so-called M-shaper. This other type of beam shaper yields a beam that is similar to a Top Hat beam. The difference resides in the shape of the borders in that there is a kind of overshoot before falling abruptly to zero. A cross profile of such beam would look to something similar to an M letter and hence the name. This type of beam is used to homogenize the exposure over a line area when the laser is being used with a scan system.
