An optical element that generates multiple output beams from a single input beam is referred to as beam splitter.
The most basic of these types of elements is the plate beam splitter in which an input beam is split into two different beams. The two new beams are the transmitted and the reflected beams respectively and their directions are usually orthogonal to each other, although that will depend on the input beam’s angle of incidence. The input beam characteristics like beam size and divergence are retained in the two new beams.
Another type of beam splitter that is based on a different operating concept is the micro lens array which consists of a series of small lenses, or lenslets, that share the same size and radius of curvature. An input beam is partitioned into many smaller beams that are brought to focus at the focal plane at each lenslet.
Another type of beam splitter that surpasses in versatility and efficacy both elements from above is the diffractive beam splitter. Unlike the previous beam splitter elements that work on the principle of light refraction, a diffractive beam splitter exploits the wave nature of light so the output transmission can be understood to be an interference effect.
In a diffractive beam splitter the input beam is turned into an array of multiple beams that can be arranged in any geometrical configuration. Each new beam shares the same characteristics of the input beam. Thus, the size and inherent divergence of the new beams is the same as the one from the input beam. Moreover, the angular orientation, or the spatial separation, among the new beams can be designed to any desired value.
Given all these remarkable features, a diffractive beam splitter finds applications in many industrial and academic fields. For instance, one of the extra beams generated by the beam splitter can be designed to be with very low power to be used for monitoring laser power in the system, avoiding having to measure power directly on the processing beam. Another totally different application can be found in aesthetic treatments in which a multi spot diffractive beam splitter generates a closely packed array of beams at the focal plane of a medical laser. Once on the patient’s skin, this irradiance pattern results on a larger area and, even more important, on a more efficient healing process. This stems from the presence of the gaps among the many spots that facilitate epidermal cell migration.