Holo/Or FAQ
General
Q: What is a DOE?
A: A DOE (Diffractive Optical Element) is a passive micro-optical component that shapes an incoming laser beam into a desired output. It works c by generating a phase delay on the laser beam thus it is purely transmissive (no absorption).
Q: What is so special about DOEs? why use them?
A: DOEs have no angular tolerance. I.e, a diffractive beam splitter or beam shaper will have the same angles regardless of production tolerances. This makes DOEs excellent in laser beam shaping applications where high precision is needed, such as precise micro-machining, diagnostic instruments, lithography and measuring and metrology systems. In addition, DOEs can realize complex optical functions in a single compact and robust surface and their design flexibility allows Holo/Or to design any shaping function easily and with low NRE costs.
Q: Can a DOE work for several wavelengths?
A: Generally, No. A DOE is designed to operate most effectively at a nominal wavelength. However, in some cases (wavelengths are close together, or cases of diffractive lens/prisms), it is possible to use a single DOE for several wavelengths. Holo/Or offers some micro-refractive solutions (PT, BD) for cases where several wavelengths need to be shaped by a single component.
Q: How sensitive is a DOE to the wavelength bandwidth? Must the wavelength be exteremly precise?
A: Most DOE types can work well within a bandwidth of +-2% of their design wavelength. I.e., a typical DOE designed for 1064nm will perform within spec in the range 1043-1085nm.
Q: Are Holo/OR DOEs suitable for high power lasers?
A: Holo/Or specializes in high power laser beam shaping. Our DOEs are made of monolithic fused silica/ ZnSe and coated with high LIDT AR coatings. As such, they can handle high power levels. The rule of thumb is, if you have a fused silica/ ZnSe optic in your system and it is not damaged by your laser, you can use our DOEs in your system. For detailed laser damage threshold data, see our LDT page.
Q: Are DOEs sensitive to laser polarization? Do they effect the polarization of the output?
A: Our DOEs are not sensitive to polarization and have no effect on the polarization of the output beam.
Q: What is Zero order? Is it a major concern?
A: Zero Order (ZO) is a fraction of the laser energy that is not diffracted. Typically, it is 0.2-0.5% of the energy, depending on the DOE type. When using a focusing lens, this ZO can appear as a spot at the original position of the focus. Holo/Or takes care to keep the effect of ZO manageable, by tight production tolerances and using design methods that make ZO defocused, when necessary. Thus, for most applications the effect of ZO is not a major concern.
Q: What is the difference between transmission efficiency and overall efficiency of DOEs?
A: Transmission efficiency refers to energy coming out of the DOE vs. the input. This is mostly determined by the AR coating or lack of it, as our elements have almost no absorption. Overall efficiency is the transmission efficiency, multiplied by the diffractive efficiency, with diffractive efficiency defined as he fraction of energy in the desired spot/shape vs the total energy in the output from the DOE. For example, if a 1X3 beam splitter has 86% efficiency and 100% transmission efficiency, it means that out of all laser input power, 86% will be divided between the desired 3 output beams, with 14% going to higher orders.
Q: How should I place the DOE in the beam path? with the patterned or the flat surface towards the beam?
A: In general, it does not matter. The DOE will perform the same for both cases. For practical integration reasons, it is often better to place the DOE with the flat side towards the input beam, since the DOE is often followed by a tube or other mechanical assembly and a lens, and in this configuration the patterned surface is less exposed to dust and other pollution as it is internal.
Production
Q: Where are the DOEs produced? Do you use an external fab?
A: Holo/Or LTD manufactures all DOEs in-house at our labs in Israel, including design, production & testing.
Q: How do you mark the element?
A: See our marking rules. The arrow is aimed at the diffractive surface.
Q: How do you produce DOEs?
A: Holo/Or uses standard semi-conductor industry methods to produce DOEs, including lithography and plasma etching. Our phase steps typically have extremely sharp side walls with angles of >870.
Q: Do you have quality certificates?
A:Holo/Or has a culture of excellence and a deep commitment to customer satisfaction. We are ISO certified; our certification is here https://www.holoor.co.il/wp-content/uploads/2021/12/ISO-Certificate-Eng2021-2024.pdf
Q: I found a relevant element in your products page, but the dimensions are wrong for my system. Can you produce this with different dimensions?
A: Yes, we can! We can re-size designs to new element dimensions for a modest resize fee. Our limit is currently 150mm diameter for fused silica elements.
Modelling
Q: Can you simulate the performance of your element in my system?
A: We at Holo/Or support our customers to the best of our ability. This may include simulation of DOEs performance with in-house tools (ideal focus optics) and simulations in Zemax™ in certain cases. We also publish many tutorials on modelling our elements and provide Blackboxes. Please contact us with your specific request.
Q: I am interested in a complex optical system that will achieve a certain non-trivial output. Can you simulate and quote such systems?
A: For complex, non-trivial systems, we typically offer an initial feasibility study. Once you order the study, Holo/Or will do an initial modelling of the system and provide a report suggesting an optical solution (if there is one) and giving initial simulations of performance.
Beam shapers
Q: I have a multimode laser, what type of beam shaper can I use?
A: Multi-mode lasers with low temporal coherence can be best shaped by diffusers, such as our diffractive diffusers family.
Q: I have a Top Hat beam shaper, and I cannot get results similar to simulations/ specs. What can be the cause?
A: Top hat beam shapers are sensitive to many tolerances, including input beam size, laser M2, beam centration and defocus. It is recommended to follow our installation manual to troubleshoot the issues , and if you still cannot reach the desired performance, contact us.
Q: Does the beam shaper require an additional focusing lens?
A: Typically, yes. We at Holo/Or design our beam shapers to have no lens power, so that they can be used with different focus lenses to achieve different shape sizes at focus. This gives our customers the flexibility to choose focus optics that fit their shaping needs. For special cases where this is preferable, Holo/Or can design and produce focal elements, that combine the functions of the beam shaper and a focus lens with a certain fixed EFL.
Q: Does a beam shaper create a flat top beam?
A: No. The beam shaper creates a flat top spot at the focus plane, when focused by an external lens. To create a collimated flat-top beam, one must use a collimated top hat module. For most practical applications, the need is for flat top at a certain focus plane, thus a single beam shaper component is a good solution.
Q: Is the phase flat at the focus plane, when the intensity shape is flat-top ?
A: No. The phase is smooth and has no speckles (thus suitable for interference), but it is not flat.
Q: Can I use any beam size with a beam shaper?
A: No, beam shapers are designed to accept a very well-defined input beam size. Deviation of +-5% are usually acceptable, but larger deviations result in non-uniform shaping.
Q: my laser beam is single mode, but has some slight ellipticity. Can I use a beam shaper?
A: Generally, yes. If ellipticity is weak (1.2 major to minor axis ratio or less), shaping functionality will be good. Some weak effects may be observable on the shaped flat top spot. We will be happy to support you with simulations for a specific case.
Q: How can I find out what is the M2 of my laser?
A: Most producers give this specification in the laser datasheet. If it is not available, please share your laser model and other available data with us, and we will try to help you based on our long experience in the laser shaping market.
Q: What is the transfer region parameter in Top hat beam shaper specs?
A: Transfer region, or edge sharpness, is the width of the region over which the top hat drops from 90% of flat area intensity to exp(-2) of the flat intensity.
Q: What is the difference between positive and negative type Top Hat beam shapers?
A: Beam shapers have a waist that is smaller than the desired flat top spot, and appears at either positive defocus (before the focal plane), or at negative defocus (after the top-hat plane). A negative top hat has the waist after the focus (further than the lens), while a positive top hat has a waist before the focus plane.
Q: can you design a DOE that will give any arbitrary shape?
A: In general, yes. Shaping is limited by constraints such as the diffraction limited spot size of the system and maximal angle, but within these constrains we can design any shape, including asymmetrical distributions.
Q: Can you guarantee a certain uniformity value of the flat top area ?
A: The shaping performance of beam shapers (both flat top diffusers and Top hat beam shapers) is a system dependent parameter. i.e., the laser quality, input beam size, beam profile, focusing optics and many other parameters effect the flat top uniformity. As such, Holo/Or cannot guarantee parameters that we do not control- we will be happy to provide simulations for pre-defined conditions.
Beam splitters
Q: How does a diffractive beam splitter work?
A: A diffractive beam splitter (also called multi-spot element) is a periodic phase structure , similar to a grating. This structure splits the incoming laser beam into discreet orders at well defined separation angles, each spot is an exact replica of the input beam in terms of beam size, polarization etc.
Q: What does uniformity mean?
A: Uniformity is the contrast between the strongest and weakest spots generated by the splitter (assuming all are designed to be equal) , normalized by their sum . For example, if the strongest order is 11mJ and the weakest 9mJ, uniformity is (11-9)/(11+9)=0.1= 10% .
Q: I see that beam splitter efficiency is less than 100%, where does the energy go? Is it absorbed?
A: No, our DOEs have almost no absorption (same as laser grade flat windows). The energy that is not counted in efficiency goes to undesired higher orders. These are spots outside of the desired array of spots generated by the diffractive beam splitter. Typically, they are much weaker than the desired spots, less than 15%, and have no process effect. In cases where the application is sensitive to undesired orders, Holo/or can create custom designs where the strong undesired orders are suppressed.
Q: What is a HEDS/HEQS beam splitter?
A: High Efficiency Double/ Quatro beam splitters (HEDS/HEQS) are a special family of beam splitters that are not periodic. Instead, they are basically made of 2 or 4 different diffractive prisms , each directing a part of the beam to a different direction. As such, they have an extremely high efficiency and can have an effect on sub-beams shape (and M2) when the input is a single mode laser.
Beam Foci
Q: What solutions do you offer for cutting of transparent materials?
A: See our glass cutting page . We provide solutions for simple Bessel beam generation (diffractive axicons), focus splitting to multiple foci and our unique to modified Z flat-top laser cutting module (DeepCleave).
Q: What is the difference between positive and negative type diffractive axicons in glass cutting?
A: See our Elongated focus page. In general, when used with an external focus objective, a negative axicon has the Bessel elongated focus region after the objective focus plane. A positive diffractive axicon has the elongated focus region before the objective focus plane.
Q: I want to cut/ drill into metal/ rough diamonds/ceramics. Can I use beam foci elements?
A: To function, our Foci elements need the beams to be un-obstructed and not diffused. Opaque or rough ground surfaces destroy the phase of beams generated by beam foci elements and thus no effective shaping will occur after encountering these types of surfaces.
Q: Why is a DeepCleave Module better than just a simple diffractive axicon?
A: A DeepCleave module is a full cutting optic that will generate a flat top intensity profile along the focal axis with a spot size <2um. A simple axicon generates a standard, non-flat top Bessel Beam profile, which wastes much energy on the below-threshold tail. An axicon typically requires external focus optics to achieve reasonable work distance, unlike the DeepCleave which is stand-alone module and creates the focus itself. See the comparison in our glass cutting application notes
Q: Does a DeepCleave module come with protective window?
A: All DeepCleave modules have an option for adding a protective window provided by Holo/Or. This will have an effect on working distance, reducing it by ¬1.5mm.
