Since their invention, laser systems have become progressively an important tool in many industry sectors. The capacity of a laser beam to condense enough light energy for marking or ablation makes them a very attractive solution in many cases of practical interest. In this regard, the radiance density of a laser beam can be further enhanced by altering the Gaussian radiance distribution that is very often the nominal mode for most laser systems. A laser beam that is considered to be Gaussian can be described by a smooth radiance peak at the centre of the beam that then slowly decays as it reaches the edges. According to the mathematical formulation of Gaussian beams, the radiance never reaches a complete zero value. For this reason, a Gaussian beam is said to be unbounded although in practice a threshold value can always be assumed.
More often than not, this Gaussian radiance is never the best choice for a laser beam in a given application. A more ideal type of beam will be one in which the energy is distributed evenly over a given, finite, area and that is surrounded by steep, abrupt, fall of energy distribution. This type of laser beam radiance is referred to as a Flat Top laser beam. With a Flat Top Laser beam the treated area is well bounded and, unlike the situation with a Gaussian beam, there is no light leakage into adjacent areas. This maximises the throughput of the laser system. Also, due to the uniform radiance plateau, the exposure to light is constant and a more precise process can be achieved.
Flat Top Laser beams usually do not emerge naturally from laser systems so an optical element to perform this conversion from Gaussian to Flat Top Laser beam has to be included along the optical train. When the light is monochromatic and highly coherent, the best option is to use a diffractive optical element that is a filter like optical component. This type of element is a piece wise element that works by exploiting the wave nature of light. The transformation required is encoded into the array of pixels and by virtue of light propagation the conversion from Gaussian to Flat Top beam is accomplished.
There are some laser systems which are multimode and with a lower degree of coherence. For these lasers a more suitable choice of light converting element will be a micro lens array.
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