Introduction
A laser beam is characterized by a coherent, monochromatic irradiance with a Gaussian profile, where the beam intensity is strongest at the center of the beam and decays towards the edges of it. If looking at the intensity profile on the working plane, this radiance profile results in a spot that has strong energy at the center and continuously fades outside of the center until the energy level reaches zero.
In many laser applications, where there is an advantage for a clear border between the treated and the untreated area, this energy profile is not optimal.
To achieve an optimal distinction between the treated and untreated zones, it is advised to use a laser beam shaper.
A laser beam shaper is an optical component that modifies the intensity profile of the incident beam to create a well distinguished spot shape with sharp edges, so that the ratio between energy level inside the spot and out of it is as close to 100% as possible.
Another characteristic of the laser beam shaper is the energy distribution inside the spot that can be controlled, thus enabling a more accurate, homogeneous and controlled process with minimal energy waste.
Holo/Or offers several types of passive, non-polarizing, laser beam shaping optics, the common ones being:
- Top hat beam shaper
- Diffractive diffuser
- Microlens array
- Broadband diffuser
Top hat beam shaper
A top hat beam shaper, also known as flat top beam shaper, is the high-end option applicable for laser systems that use single mode low M^2 laser beams (typically M^2 < 1.5). A flat top laser beam shaper is a diffractive optical element (DOE) that transforms the Gaussian beam into a flat-top beam with uniform intensity inside a well-defined shape with pre-designed angular dimensions, and a very sharp energy drop at the shape edges (the “transfer region”).
DOEs are designed to work with a specific wavelength in which they enjoy a perfect angular accuracy and very low production tolerances thanks to their manufacturing process, making them the best solution for laser applications requiring high accuracy. They are fabricated onto optical windows making them flat, thin and lightweight, properties that bring added value to many customers requiring a compact solution.
Diffractive diffuser
The diffractive diffuser is best used in laser systems with low coherence laser beams. It diffracts the beam and then scrambles it onto itself to achieve a highly homogenous, speckle free beam. The diffractive diffuser can be designed to any desired spot shape and size including free-form spot shapes, with controlled energy distribution within the spot (for example a bat-wing distribution, a non-symmetric tail and many more).
Much like the top hat beam shaper, the diffractive diffuser is a DOE and thus it provides the same benefits of sharp transfer region, perfect angular accuracy, very low production tolerances and compactness. Unlike the flat top laser beam shaper, the diffractive diffuser is not sensitive to centration or beam size, making it very easy to integrate into existing systems.
Microlens array
The microlens array (MLA) is possibly the most common and well known beam shaping solution, but perhaps also the most limited one amongst the solutions offered here for beam shaping purposes. As its name implies, it comprises an array of microlenses arranged in a certain specific periodic grid – typically round, square or cylindrical lenses in a square, hexagonal or a linear grid. Used in a defocus regime, or as a part of a fly-eye-diffuser pair, it can produce diffusion and flat-top shaping for less coherent beams.
Unlike the diffractive optics beam shaping solutions stated above, a MLA is a refractive beam shaping option making it applicable for use in polychromatic systems where more than a single wavelength requires the same shaping in the same optical path, or where white light or highly divergent sources such as light emitting diodes (LEDs) are in use.
The microlens array generates a fairly homogenic beam with high efficiency, and can be designed to produce geometric spot shapes (round, square, line etc.), however due to it’s refractive sub-aperture nature, it has an angular tolerance and fuzzier, softer edge compared to a diffractive diffuser, and is thus less recommended for systems requiring high precision.
Broadband diffuser
The broadband diffuser (BD), also known as engineered diffuser, is a special flat-top beam shaping micro-refractive diffuser much similar to MLA, however with pseudo-random arrangement of the lenslets which results in far better homogenization quality compared to a simple MLA. By modifying the sub-aperture optical functions beyond the profile of a simple lens one can achieve versatile control of the shape, including M Shapes (Bat Wing) or even flat profile rings.
BD are specially designed laser beam shaping solutions for applications where multiple lasers are used in the same optical path for example: RGB module, tunable lasers and frequency doubled lasers operating over a broad spectral range.
BD elements offer high homogeneity with the same performance over a wide wavelength spectrum from IR to UV, high efficiency and no zero order.
Laser beam shaping applications
There are various applications that utilize laser beam shaping and reap the benefits. Some of the more common ones include:
- Accurate material processing applications such as:
- Laser cutting
- Laser lift-off
- Ablation
- Drilling.
Optical designers in these applications typically implement a top-hat DOE in their systems.
- Area Laser heat treatment applications requiring high process uniformity, such as:
- Welding and brazing in material processing
- Hair removal, tattoo removal and body contouring in the aesthetic medical devices.
Optical designers in these applications typically implement either a diffractive diffuser or a broadband diffuser.
- Projection systems requiring a uniform projection, such as:
- Laser cinema projector
- Time of Flight projector for 3D sensing and machine vision
- Laser light shows
Optical designers in these applications typically implement a broadband diffuser.
How to choose a beam shaping solution?
Choosing a laser beam shaper can depend on many variants and there is no clear cut answer to which shaper type is the best for what application. The below qualitative table summarizes the differences and advantages of each type and will try to direct you to the correct solution for your needs.
Not sure what you need?
contact us with your needs and our application engineers will assist you in finding the solution for you!
| Top hat beam shaper | Diffractive diffuser | Microlens array | Broadband diffuser | |
| Design wavelength | Single wavelength | Single wavelength | Multiple wavelength / Polychromatic | Multiple wavelength / Polychromatic |
| Wavelength Range | UV to IR | UV to IR | UV to IR | UV to IR |
| Source type and beam quality | Single mode Laser, M^2<1.5 | Multi mode Laser, can work with single mode but generate strong speckling | Multi mode Laser, RGB module, Tunable lasers, Frequency doubled lasers, LEDs | Multi mode Laser, RGB module, Tunable lasers, Frequency doubled lasers, LEDs |
| Spot shape | Any
| Any | Round, Square, Rectangle, Line, M-shape (“bat-wing”) | Round, Square, Rectangle, Line, M-shape (“bat-wing”) |
| Diffusion angle | Small angles, exact, not affected by temp. | Small and medium angles, exact, not affected by temp. | Medium and wide angles, +/-10% tolerance, may be affected by temp. | Medium and wide angles, +/-10% tolerance, may be affected by temp. |
| Efficiency | Very High | Design dependent | High | High |
| Uniformity | High | High | Moderate | High |
| Transfer region | Very sharp | Sharp | Moderate | Moderate |
| Sensitivity to tolerances: beam size, alignment and centration | Sensitive to all | Not sensitive | Not sensitive, requires minimal beam size | Not sensitive, requires minimal beam size |
| Materials | ZnSe, FS, UV FS | ZnSe, FS, UV FS, Polymer on Glass, Polycarbonate | FS, UV FS, Polymer on Glass, Polycarbonate | FS, UV FS, Polymer on Glass, Polycarbonate |
| Application notes for further reading | BEAM SHAPER / TOP-HAT | HOMOGENIZER / DIFFUSER | ||
| Product catalog | BEAM SHAPER | DIFFUSERS | MICRO LENS ARRAY | BROADBAND DIFFUSER |
