Diffractive optics has evolved into an effective way to shape and split beams. Their being lightweight and compact and their ability to be easily integrated into optical systems make them more beneficial than refractive optics. Also, diffractive optics can do many optical functions in one element. Advances in diffractive optical elements (DOEs) have made them a standard component in medical and aesthetic lasers, laser material processing, and structured light projection systems. Improvements in their design and manufacturing processes have decreased undesired orders and zero order while enhancing uniformity and achieving higher diffractive efficiencies.

How DOEs Work

DOES are diffractive microrelief patterns that manipulate an incoming laser beam’s phase to create a desired intensity profile at the lens focus-plane. They are characterized by the fraction of power directed into the desired direction versus the total input power.

Diffractive optical elements can either be a binary element or a multilevel element. Generally, more level uses mean higher efficiency and lower zero order. But, some constraints arise out of the manufacturing process. The process of making a high-laser-damage-threshold DOE is based on photolithography and dry plasma etching steps. Common processed substrates include zinc selenide, fused silica, and sapphire which are all ideal for high-power laser systems.

Reducing Etching Errors

Manufacturing tolerances like etching depth and feature size are likely to induce high zero order and lower uniformity, degrading the DOE’s overall performance. To offer high-quality elements and minimize the unintentional lithography and etching errors, it is important to define manufacturing tolerances per design, considering the number of design levels and specifications.

DOEs for Beam Shaping and Beam Splitting

Beamsplitter DOEs are utilized for splitting a laser beam into a predefined number of beams that possess the original beam’s unique characteristics and a desired angle of separation. They can generate either a one-dimensional beam array or a two-dimensional beam matrix, depending on the element’s diffractive pattern. Beamsplitters are recognized for their diffractive efficiency, zero-order value, spots uniformity, and undesired orders value.

Meanwhile, beam-shaper DOEs are used for transforming a Gaussian incident laser beam into a uniform-intensity spot of a square, round, line, or rectangular shape with sharp edges in a certain work plane. Products such as diffractive axicons, top hats, diffusers, and vortex lenses belong in this category. Specifications of beamshaper DOEs include diffractive efficiency, zero order value, and transfer region. With advances in DOE design and manufacturing techniques, designs for many traditional products like challenging beamsplitter and diffractive axicon beam shapers configurations have improved.