DOE assembly "Cross Hair"

Q: Glass optics vs. acrylic optics – when which?

Acrylic optics (PMMA plastic): low cost, light, dimensionally stable. Optically very good in standard applications, but temperature-sensitive – the refractive index changes with temperature, shifting the focus when variation exceeds ±5 °C. Perfectly adequate for indoor applications with stable conditions. Glass optics: heavier, more expensive, but temperature-stable. The refractive index stays nearly constant across wide temperature swings. Ideal for: outdoor mounting, unheated halls, machines with large temperature swings (welding, sawmills in summer/winter) and applications needing high repeat accuracy over long periods. Glass optics are available as an optional upgrade on our KLM and LLM modules.

Q: Dielectric mirrors vs. metallic mirrors – what are the differences?

Metallic mirrors (aluminium, silver, gold): reflection via a thin metal coating. Typically up to&gt;98 % reflectivity in the visible range. Benefits: broadband (from UV to IR), low cost. Drawbacks: lower power handling, prone to oxidation (especially silver), reflectivity depends on angle of incidence. Dielectric mirrors: reflection via multi-layer glass coatings that reflect through interference. Typically &gt; 99 % reflectivity in the optimized spectral range. Benefits: extremely high reflectivity, high power handling, no oxidation. Drawbacks: narrowband (optimized for a specific wavelength), more expensive. Our LS 50 is a dielectric mirror with &gt; 96–98 % reflectivity in the 400–700 nm range.

Q: What is the aperture of an optic?

The aperture is the usable opening diameter of an optic – the area through which light can enter the lens. Measured in millimetres. A larger aperture collects more light from the source – particularly important for laser diodes with a large emitter (e.g. Nichia NDG7575). Our Colli-LA collimator has a 5 mm aperture, gathering significantly more light than typical 3 mm collimators. Practical effect: brighter, more uniform output beam and less light lost at the diode edge. Related metric: the numerical aperture (NA) describes the ratio of aperture to focal length – and therefore the optic's acceptance angle.

Q: What does the focal length of a lens mean?

The focal length is the distance from the principal plane of a lens to the focal point, where parallel incoming light rays intersect. It is measured in millimetres (e.g. f = 4 mm on our Colli-LA). For collimators the focal length determines at which distance from the laser diode the lens must be mounted to collimate the beam – ideally the diode emits from the focal plane. Shorter focal lengths (3–4 mm): high aperture, good light gathering, compact – ideal for 12 mm modules. Longer focal lengths (8–20 mm): smaller aperture, less light gathering, but a narrower collimated beam – for long-distance applications.

Q: What is an AR coating (anti-reflective)?

An AR coating (anti-reflective coating) is a thin, multilayer coating on optical glass surfaces that reduces reflection and increases transmission. At an uncoated glass–air interface typically 4–8 % of the light is lost to reflection. A modern AR coating reduces this to &lt; 0.5 % per interface. For a lens with two interfaces that means 92 % transmission uncoated vs. &gt; 99 % coated. Benefits: higher optical efficiency, less stray light, lower back-reflection load on the laser diode. AR coatings are wavelength-specific – a coating for 532 nm behaves differently at 650 nm. Always check the spectral range of the optic.

Q: What is a collimator and what does it do?

A collimator is an optical lens or lens system that converts a divergent light beam into a parallel beam. Essential with laser diodes: the bare diode emits a strongly fanned-out beam; the collimator turns it into a bundled, parallel beam. Construction: usually an aspheric glass lens in an M9 × 0.5 or M12 threaded housing. High-quality collimators feature an AR coating (anti-reflective) for minimal light loss at the interfaces. Key parameters: focal length (typ. 3–6 mm), aperture (typ. 4–8 mm) and the AR coating's spectral range (e.g. 420–680 nm for visible light). Glass collimators are more temperature-stable than cheaper acrylic lenses.

Q: What is pick-by-light used for?

Pick-by-light is an optical guidance system used in logistics and assembly: a laser shows the worker the next position to pick or the location of the next work step. Instead of reading lists or checking screens, the worker simply follows the laser. Benefits: fewer pick errors, faster cycle times, shorter training, low noise. Used in: order-picking warehouses (picking from shelf compartments), manual assembly (which screw next), placement (which position on the workpiece), packing (which box gets the item). Our DOE positioning lasers are well suited because they project clearly visible, defined patterns.

Q: How large is the pattern at a given distance?

The image size scales linearly with distance. With a PLM module at approx. 30° opening angle, 1 m distance gives an image of around 30 cm diagonal. At 2 m this doubles to 60 cm; at 0.5 m it halves to 15 cm. Recommended operating distance: 5 cm to approx. 100 cm. Beyond 100 cm the line sharpness drops noticeably, because DOE optics widen the line proportionally with distance. For very large distances we recommend the FloorPoint (100 mW at 532 nm) or an ILP laser projector.

Q: Which DOE patterns are available?

We offer five standard patterns: Laser crosshair „CH“ – classic +-cross for centring. Circle „Circle“ – marking circular areas (e.g. drill positions). Search field „SF“ – a larger highlighted area for visual orientation. Square „SQ“ – rectangular marking for pallet positions or boxes. Dot grid – on request for special patterns such as pick grids. The standard patterns are encoded in the product codes (e.g. PLM-30-650-CH = crosshair, PLM-10-650-SQ = square). Custom DOEs with company-specific logos or special alignment marks are available on request.

Q: What do the laser classes 1M and 2M mean?

Classes 1M and 2M according to EN 60825-1 stand for „Magnifying Optics“ – lasers that are safe under normal conditions but whose radiation can become hazardous when viewed through optical aids such as magnifiers, binoculars or microscopes. With DOE positioning lasers the optical power is spread across the pattern – but if a lens were to refocus the radiation, the power density could reach hazardous levels. Practical consequence: safe for normal industrial use without safety goggles. Prohibited: viewing the beam through magnifiers, binoculars or microscopes.

Collimator: Glass for Green

DOE-Ass-Crosshair: DOE optical assembly “cross hair” with collimator, screw-in type (M9 × 0.5) for MediaLas laser modules. Generates the pattern from a point laser.

€55.36

Collimator

Acrylic

Glass for Green

Glass for Red

Product number: DOE-Ass-Crosshair.1

DOE assembly "Cross Hair"

DOE Assembly, M9 Cross Hair for Laser Modules: Complete optical assembly including a DOE (diffractive optical element) and collimator, designed to screw into most MediaLas laser modules with an M9 × 0.5 thread. Generates a “cross hair” projection pattern from a point laser. DOEs form a bright spot in the center.

Technical Specifications

Max. Laser Power	200 mW
Image size	approx. 30 cm at 1 m
Focus range	Approx. 5 cm to approx. 150 cm, recommended up to max. 100 cm
External thread:	M9 x 0.5

Collimator:	Acrylic, Glass for Green, Glass for Red

Glass optics vs. acrylic optics – when which?

Acrylic optics (PMMA plastic): low cost, light, dimensionally stable. Optically very good in standard applications, but temperature-sensitive – the refractive index changes with temperature, shifting the focus when variation exceeds ±5 °C. Perfectly adequate for indoor applications with stable conditions. Glass optics: heavier, more expensive, but temperature-stable. The refractive index stays nearly constant across wide temperature swings. Ideal for: outdoor mounting, unheated halls, machines with large temperature swings (welding, sawmills in summer/winter) and applications needing high repeat accuracy over long periods. Glass optics are available as an optional upgrade on our KLM and LLM modules.

Dielectric mirrors vs. metallic mirrors – what are the differences?

Metallic mirrors (aluminium, silver, gold): reflection via a thin metal coating. Typically up to>98 % reflectivity in the visible range. Benefits: broadband (from UV to IR), low cost. Drawbacks: lower power handling, prone to oxidation (especially silver), reflectivity depends on angle of incidence. Dielectric mirrors: reflection via multi-layer glass coatings that reflect through interference. Typically > 99 % reflectivity in the optimized spectral range. Benefits: extremely high reflectivity, high power handling, no oxidation. Drawbacks: narrowband (optimized for a specific wavelength), more expensive. Our LS 50 is a dielectric mirror with > 96–98 % reflectivity in the 400–700 nm range.

What is the aperture of an optic?

The aperture is the usable opening diameter of an optic – the area through which light can enter the lens. Measured in millimetres. A larger aperture collects more light from the source – particularly important for laser diodes with a large emitter (e.g. Nichia NDG7575). Our Colli-LA collimator has a 5 mm aperture, gathering significantly more light than typical 3 mm collimators. Practical effect: brighter, more uniform output beam and less light lost at the diode edge. Related metric: the numerical aperture (NA) describes the ratio of aperture to focal length – and therefore the optic's acceptance angle.

What does the focal length of a lens mean?

The focal length is the distance from the principal plane of a lens to the focal point, where parallel incoming light rays intersect. It is measured in millimetres (e.g. f = 4 mm on our Colli-LA). For collimators the focal length determines at which distance from the laser diode the lens must be mounted to collimate the beam – ideally the diode emits from the focal plane. Shorter focal lengths (3–4 mm): high aperture, good light gathering, compact – ideal for 12 mm modules. Longer focal lengths (8–20 mm): smaller aperture, less light gathering, but a narrower collimated beam – for long-distance applications.

What is an AR coating (anti-reflective)?

An AR coating (anti-reflective coating) is a thin, multilayer coating on optical glass surfaces that reduces reflection and increases transmission. At an uncoated glass–air interface typically 4–8 % of the light is lost to reflection. A modern AR coating reduces this to < 0.5 % per interface. For a lens with two interfaces that means 92 % transmission uncoated vs. > 99 % coated. Benefits: higher optical efficiency, less stray light, lower back-reflection load on the laser diode. AR coatings are wavelength-specific – a coating for 532 nm behaves differently at 650 nm. Always check the spectral range of the optic.

What is a collimator and what does it do?

A collimator is an optical lens or lens system that converts a divergent light beam into a parallel beam. Essential with laser diodes: the bare diode emits a strongly fanned-out beam; the collimator turns it into a bundled, parallel beam. Construction: usually an aspheric glass lens in an M9 × 0.5 or M12 threaded housing. High-quality collimators feature an AR coating (anti-reflective) for minimal light loss at the interfaces. Key parameters: focal length (typ. 3–6 mm), aperture (typ. 4–8 mm) and the AR coating's spectral range (e.g. 420–680 nm for visible light). Glass collimators are more temperature-stable than cheaper acrylic lenses.

What is pick-by-light used for?

Pick-by-light is an optical guidance system used in logistics and assembly: a laser shows the worker the next position to pick or the location of the next work step. Instead of reading lists or checking screens, the worker simply follows the laser. Benefits: fewer pick errors, faster cycle times, shorter training, low noise. Used in: order-picking warehouses (picking from shelf compartments), manual assembly (which screw next), placement (which position on the workpiece), packing (which box gets the item). Our DOE positioning lasers are well suited because they project clearly visible, defined patterns.

How large is the pattern at a given distance?

The image size scales linearly with distance. With a PLM module at approx. 30° opening angle, 1 m distance gives an image of around 30 cm diagonal. At 2 m this doubles to 60 cm; at 0.5 m it halves to 15 cm. Recommended operating distance: 5 cm to approx. 100 cm. Beyond 100 cm the line sharpness drops noticeably, because DOE optics widen the line proportionally with distance. For very large distances we recommend the FloorPoint (100 mW at 532 nm) or an ILP laser projector.

Which DOE patterns are available?

We offer five standard patterns: Laser crosshair „CH“ – classic +-cross for centring. Circle „Circle“ – marking circular areas (e.g. drill positions). Search field „SF“ – a larger highlighted area for visual orientation. Square „SQ“ – rectangular marking for pallet positions or boxes. Dot grid – on request for special patterns such as pick grids. The standard patterns are encoded in the product codes (e.g. PLM-30-650-CH = crosshair, PLM-10-650-SQ = square). Custom DOEs with company-specific logos or special alignment marks are available on request.

What do the laser classes 1M and 2M mean?

Classes 1M and 2M according to EN 60825-1 stand for „Magnifying Optics“ – lasers that are safe under normal conditions but whose radiation can become hazardous when viewed through optical aids such as magnifiers, binoculars or microscopes. With DOE positioning lasers the optical power is spread across the pattern – but if a lens were to refocus the radiation, the power density could reach hazardous levels. Practical consequence: safe for normal industrial use without safety goggles. Prohibited: viewing the beam through magnifiers, binoculars or microscopes.

DOE optics vs. classic lens optics – pros and cons?

Classic lens optics (cross-line laser): very sharp, narrow lines; brightest at the centre, fading towards the line ends (Gaussian profile). Ideal for precise centring where line sharpness is critical. DOE optics (positioning laser): even brightness across the entire pattern, defined outer boundary, arbitrary patterns possible. Lines are inherently a little wider and less sharp than with lens optics. When to choose which? Classic optics for micrometre-level centring and microscope work. DOE optics for operator guidance, pick-by-light and anywhere the whole pattern must be evenly visible.

What is a DOE (diffractive optical element) and how does it work?

A DOE – diffractive optical element – is a special optic that generates a pattern through diffraction rather than through classic refraction at lenses. Instead of just a single line or dot, arbitrary patterns are formed: crosshairs, circles, squares, search fields, dot grids or marking symbols. The advantage over classic lens optics: constant brightness across the entire pattern area – even the outer edges of a crosshair are as bright as the centre. The trade-off: lines are inherently a little wider than with classic lens optics. DOE modules are ideal for operator guidance, pick-by-light and position indication.