What are Diffractive Beam Splitters
Diffractive beam splitters, or Multi-spot elements, are Diffractive optical elements (DOEs) that split a laser beam into multiple beams with equal separations. They are based on grating-like phase structures that diffract the beam into discrete orders, unlike traditional beam splitter cubes/window, where the light is split into 2 rays – a reflected ray and a transferred ray. Traditional beam splitters are reflection-based splitters, where a part of the beam is reflected (usually at 90 degrees) while the rest of the beam continuous on the original trajectory. This is done either by a dielectric coating with a tailored reflectivity, or, in the case of a polarizing beam splitter, by a prism made of a birefringent material that reflects one polarization while transmitting the other.
General Applications of Beam Splitters
Beam splitters are widely used in optical systems for a variety of applications. These can be in general divided to two main groups:
- Use for laser sampling/ feedback loop component- In this regime, the laser beam splitter glass is used to sample a small fraction of the laser beam in a manner similar to our sampler DOE. This fraction is then measured to keep the laser system within a tight range of performance. Unlike beam splitter glasses used for sampling, the sampler DOE is often used to sample the beam profile in real time and not just the power.
- Use as main functional component – The beam splitter creates beams that go through different channels (for example in an interferometer), or to create identical channels to increase throughput, as in the case of industrial or aesthetic laser processes. In such cases, splitting into more than two beams is highly desirable, thus diffractive beam splitters which can split the beam to any number of desired channels are often preferred.
Advantages of Diffractive Beam Splitters
Diffractive beam splitters have several advantages compared to traditional, reflection-based beam splitters:
- DOE beam splitters can split to any number of beams, along a line or in a 2D splitting pattern, as needed.
- Intensity of each order and order arrangement can be adjusted as desired by design.
- Diffractive beam splitters create an array of beams going forward, instead of the split beams being at 90 degrees to each other. This is highly useful in cases such as parallel laser processing, where one wants to use the same optical system for all beams instead of creating two laser heads (or more), for example.
- Diffractive beam splitters are completely insensitive to the laser polarization, unlike standard beam splitters that usually have some sensitivity to polarization.
- As they are flat windows that work at an angle of incidence (AOI) of around 0, DOE beam splitters have higher laser damage Thresholds compared to reflective based splitters that work at 450
These advantages are especially pronounced in high power laser systems or 3D sensing applications, where Diffractive beams splitters are the go-to element of choice.
Diffractive Beam Splitter Applications
With our more than 30 years of experience in the high power laser market, Holo/or has intimate knowledge of laser beam splitter applications, especially for high power laser. These include:
- Aesthetic laser treatments, for example fractional laser skin treatments.
- Parallel laser scribing, scoring, ablation to increase throughput
- Multi-line lithography
- Coherent beam combining
- Direct Laser interference patterning (DLIP)
- Perforation of membranes (for example filter papers, food packaging)
- Generation of structured light (“points cloud”) for 3D sensing and metrology
