The application of laser light is becoming increasingly crucial in various modern devices to conduct numerous functions, such as medical imaging, laser printing, fibre optic communication, 3D printing, 3D imaging with LIDAR, additive manufacturing, material processing, and sensing. Even within a gaming controller or a smartphone, we can see the use of infrared light for motion control and facial detection. These devices or pieces of equipment use diffractive optical elements (DOEs) to detect, project, and manipulate the complex patterns of laser light that are essential for their operation. So, what are diffractive optical elements and what are their applications?
DOEs are flat and thin optical components that function using the principle of optical diffraction. These optical components comprise tailor-made micro-structures that change the phase of the incident light, modifying the laser’s shape and intensity profile far from the laser or at a lens’s focus.
The Characteristics of DOEs
Here are some significant characteristics of DOEs:
- DOEs are flat, thin, and lightweight optical components, therefore, they are suitable for compact systems.
- These optical elements offer negligible angular tolerances and precise output.
- DOEs possess several novel characteristics that are impossible to achieve with traditional reflective and refractive optical elements, such as the ability to combine multiple optical functions in a single DOe surface .
- DOEs offer robust, long-lasting performance.
The Categorization of DOEs
Depending on the expected optical function, DOEs are primarily categorised into Beam Shapers, Beam Splitters, and Focal shaping elements (Beam Foci).
Beam Shapers
Beam Shaper DOEs are used to manipulate the incident laser beam into a well-defined output beam with a specific angular shape and uniform or other pre-defined intensity profile. Depending on the type and quality of the input beam, it is important to determine the beam shaping method. For instance, an analytical beam shaper is ideal for single-mode lasers, while the Homogenizer or Diffuser is suitable for multi-mode lasers. One can also customise beam shapers for any expected output beam shape or size; focal beam shaping or angular beam shaping; and any input beam diameter.
Applications: The major applications of beam shapers are in laser ablation ,laser scribing, laser cutting , sensing, aesthetic-medical laser devices, and more.
Beam Splitters
The purpose of beam splitter DOEs is to split an incident laser light into various well-defined output beams with predefined intensities and separate angles. The micro-structure of the beam splitter determines the propagation angles and intensities of the diffracted beams. Therefore, one can tailor a beam splitter to produce a desired number of beams with predefined intensities and arrangements; hexagonal, square, or even random packing; as well as for any specific intensity ratio between beams.
Applications: Beam splitters have several applications, including parallel laser scribing, medical aesthetic laser treatment, surface texturing and LIDAR .
Focal shaping DOEs (Beam Foci)
Beam Foci DOEs transform the focal properties of the incident beam into an output beam with either multiple focal planes or an enhanced depth of focus (bessel like beams) , or focus diverse wavelengths into one focal plane. Therefore, one can tailor beam foci for focusing various harmonics or wavelengths of a laser into one focal plane; enhancing depth of focus, and splitting incident light into multiple foci with pre-determined separation distance.
Applications: The primary applications of Beam Foci DOEs involve transparent material processing, including glass cutting, selective laser induced etching, microscopy and metrology.
To sum up, when it comes to shaping optical beams effectively and enhancing the overall performance of an optical system, diffractive optical elements become a crucial go-to solution.
