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How the quality Beam Expander works
Posted on:
2022-05-06
Usually we take the divergence parameter of the beam as the characteristic of a perfect Gaussian laser beam. Divergence refers to the spread of light waves at a certain angle during their spatial propagation. Even perfect rays without any anomalies experience some beam divergence due to diffraction effects. Diffraction is the bending effect of light when it is cut by an opaque object, such as a knife edge. The unfolding results from the secondary wavefront array emanating from the cut edge. These secondary waves will interfere with the main wave, and at the same time, they will also interfere with each other, and at some point a complex diffraction pattern will be formed.
The far-field divergence of the quality Beam Expander defines the best collimation for a given beam diameter. It also shows that zero divergence of the beam, or optimal collimation, is impossible, since to do so requires an infinite beam diameter. But this equation also shows the possibility of improving divergence.
The most common type of quality Beam Expander originates from Galilean telescopes and typically consists of an input concave lens and an output convex lens. The input mirror transmits a virtual focal length beam to the output mirror. The general low-magnification beam expander is manufactured by this principle, because it is simple, small in size and low in price. Generally, it is designed to be as small as possible with spherical aberration, low wavefront distortion and achromatic. Its limitation is that it cannot accommodate spatial filtering or beam expansion with large magnifications.
In fact, Kepler-designed telescopes are generally used when spatial filtering or large-magnification beam expansion is required. The quality Beam Expander generally has a convex lens as the input lens, which sends the focused beam of real focal length to the output element. Additionally, spatial filtering can be achieved by placing a pinhole at the focal point of the first lens.
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