Transparent Polygon Scanning

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TPS (Transparent Polygon Scanning) is a laser scanning technology. The technology can be used for additive manufacturing. Rik Starmans developed the first laser scanner with TPS technology and named it Hexastorm<math>^{\text{TM}}</math>. Hexastorm is shown in figure 1.

Figure 1

To clarify, TPS technology is put in perspective by comparing it with Fused Filament Fabrication (FFF) technology. The smallest element of a FFF enabled printer is the nozzle which is a circle with a 300 micrometers diameter. In the first laser scanner with TPS technology, this is an elliptical laser spot which is 50 by 60 micrometers. The standard speed of a FFF printer is 50-80 millimeters per second. TPS enabled printers are able to reach a spot speed of 6.8 to 34 meters per second. The maximum scan length is 24 mm. The speed of a whole scan line is 16 to 84 mm/s.

Description

The transparent polygon scanner consists out of a laser diode which is focused directly with an aspherical lens. The bundle refracts through a transparent polygon and is directed to the surface with a 45 degrees first sided mirror. The bundle is deflected by tilting a transparent plate. The position of the laser bundle is monitored by a photo-diode. A Field Programmable Gate Array (FPGA) is used to ensure the correct timing of and stream data to the laser diode. A schematic side view and top view of the system are shown in figure 2 and 3.

Figure 2
Figure 3

A substrate can be solidified by moving the optical head in a snakelike pattern over the substrate as shown in figure 4. A more advanced scanning technology is infinite field of view.

Figure 4

The system has four advantages; it has a high optical quality, it is cost effective, it is scalable for industrial applications and there is no patent. The system has a high optical quality as the bundle is in focus over the full scan line and is incident at 90 degrees. The transparent polygon scanner thus gives a flat field projection and the system is telecentric. Details are provided in the physics section. The system is cost effective as it is able to achieve this quality without an expensive f-theta lens. Only two optical elements are needed; an aspherical lens and a transparent polygon. A reflective polygon scanner needs a thick disk as collimated bundles with a larger diameter can be focused to smaller spots. In the transparent polygon scanner shown, the laser is focused before it hits the polygon. As a result, the disk can be made thinner and therewith lighter which reduces the price of the bearing. Thirdly, the system is scalable. The maximum optical power of laser diodes becomes less as their wavelength becomes shorter. As a result, laser diodes need to be combined to give more power. It is, however, not possible to combine more than two lasers into a single bundle without interference. The electromagnetic field only allows for up to two polarizations. Companies like Kleo Halbleitertechnik therefore sell systems which use 288 laser bundles, see video. Companies which use single bundle transparent polygon scanners, like Hexastorm, have a scan angle of 90 degrees. Kleo uses multiple bundles per polygon and therefore has a scan angle of 45 degrees or less. The concept of scan angle is explained in the physics section.

Figure 5
If multiple transparent polygon scanners are used in a combined fashion, see figure 5, a substrate can be solidified at once and the snake like pattern is not needed. This might be desirable in industrial production systems.

Finally, the system is open and not patented. Hexastorm tried to raise funds for an open-hardware laser scanner via Kickstarter. This campaign failed. Corporate clients were interested in the technology and it got showcased at Hello Tomorrow. The project was not able to attract funds due to its open-hardware model.


Specifications

The Hexastorm, the first single bundle transparent polygon scanner in the world, has the following specifications:

  maximum scan length: 24 mm
  typical scan length: 8 mm
  wavelength: 405 nm
  revolutions per second: 67-350 Hertz
  spot diameter: elliptical, 50 (short axis) x 60 (long axis) micrometers
  cross scanner error: 40 micrometers
  laser driver frequency: 100 kHz
  laser frequency: 50 MHz
  optical power: 300 mW
  facets: 4

The scan speed of a transparent polygon scanner is not uniform and varies slightly. The scan speed at the center is 80 percent of that at the edges of a scan line of 8 mm. The non-uniform scan speed is mitigated by using a high speed laser with a 50 MHz pulse rate. The lower power at the edges could actually be useful, as it exposes a zone which is often illuminated twice.


Prior Art

Earlier scanners can be split into two groups; transparent and reflective polygon scanners. Laser scanners can come with a single or a plurality of bundles. The first patent for a transparent polygon scanner with a single laser bundle was filed by Lindberg in 1962. Rik Starmans build the first practical transparent polygon scanner with a single laser bundle. The Netherlands Organization for Applied Scientific Research (TNO) has filed a patent application for a transparent polygon scanner with a plurality of bundles WO 2015/160252 A1. TNO build two machines with a plurality of bundles; the Lepus Next and the Argos. The first reflective polygon scanner with a single laser bundle in additive manufacturing was used by the Institute of Physical and Chemical Research (RIKEN) in 1997. In 2015, Envisiontec got a patent US 9079355 B2 for a reflective polygon scanner with a single laser bundle in additive manufacturing to protect its Scan, Spin and Selective Photocure (3SP) technology. KLEO Halbleitertechnik sells the Speedlight 2D. The Speedlight 2D is a system which uses 9 reflective polygons and 288 laser diodes to solidify a substrate with a width of 650 mm. The reflective polygon has 32 facets and rotates at a speed of 50.000 rotations per minute, see patent US8314921B2.

Business Case

The market for laser scanning technology is extremely large. Possible applications are; laser direct imaging of printed circuit boards, additive manufacturing, laser cutters, self driving cars, photocopiers and object scanners. Already in the field of 3D printing applications can range from sintering powders to solidifying polymers or egg whites. The analysis was simplified by listing exposure technologies and light sources in the 3D printing and PCB market. This should give the reader a quick overview of what is available.

Alternative Exposure Technologies

The following alternative illumination technologies can be distinguished;

  • Polygon scanner with refractive F-theta lens and one laser bundle
    • Used by: Envisiontec, Orbotech
  • Polygon scanner with reflective F-theta lens and one laser bundle
    • Used by: Next Scan Technology
    • Notes: Reflective lenses probably make the lens lighter than a glass alternative. This might simplify the fabrication of large lenses. Reflective lenses might also be beneficial at low wavelengths. Light gets absorbed by glass in deep UV.
  • Reflective polygon scanner with multiple laser bundles
    • Used by: Manz
    • Notes: the polygon tilt angle is smaller than 45 degrees, most likely costs 1 million euro's
  • Transparent polygon scanner with multiple laser bundles
    • Used by: LDI Systems
    • Notes: LDI started as a spin-off company from TNO.
  • Digital Micromirror Device (DMD) illuminated with LEDs
    • Used by: Ucamco and Prodways
    • Notes: Ucamco uses multiple beamers adjacent to each other. This is expensive, as a result Prodways translates the beamer and illuminates a 45 degrees mirror, see Moving Light technology. If the DMD is illuminated with laser diodes this can result into multiple-slit interference. Ucamco sells beamers which use three wavelengths peaks. This can be advantageous if different resists are used or the edges need a different exposure.
  • Galvanometer scanner with Nd:YAG LASER
    • Used by: 3D Systems, Materialise
    • Notes: low power and frequency of Nd:YAG laser, due to inertia galvanometer scanners are slower than polygon scanners
  • Resonant Galvanometer Scanner
    • Notes: Can reach a line speed of 16 kHz, but the line speed is not constant, see 1 and 2.
  • Liquid Crystal Display (MSLA Technology)
    • Used by: Structo
    • Notes: Structo uses an array light source and projects through a digital mask. This technology can be scaled. It is, however, very energy inefficient see technical details. Cooling is a challenge. The technology cannot reach low wavelengths, i.e. below 400 nm. The light engine has to be in close vicinity of the reservoir. This could be an advantage for a Continuous Liquid Interface Processing (CLIP) like technology.
  • Acousto-optic deflector (AOD)
    • Used by: LPKF
    • Notes: 100 kHz position switching, no moving parts, sub-nm positioning
  • Optically Addressable Light Valve (OALV)
    • Developed by: Lawrence Livermore National Laboratory
    • Notes: The light valve is optically addressed by a projector at 470 nm which sets the transparency of the OALV. An OALV does not requires that the beam has a single mode and low divergence. The fine feature size of single mode laser beams is often limited by the thermal diffusion length. Lawrence Livermore uses two sources; laser diodes to heat up the powder and a Nd:YAG laser to initiate the process an melt the powder, see article.

The Grating Light Valve, sold by companies like Silicon Light Machines, can be used for mask-less lithography below 15 micrometers, i.e. 2.5 micrometer features and was omitted. Too few applications of the MEMS scanner developed by Fraunhofer were known to take it into consideration.

Alternative Light Sources

The following light sources have been considered;

  • Light-Emitting Diode (LED)
    • Used by: Ucamco and Prodways
    • Wavelengths: 405, 395, 385, 374, 365
    • Frequency: set by other element in the optical path, e.g. the refresh rate of the DMD chip
    • Power:<4 watt
    • Price: 5 euro's per LED
    • Note: LEDs offer less contrast and depth of field than laser diodes but can be combined as they do not produce coherent light. Texas Instrument seems to have a monopoly on DMD chips. Projection systems are sold by other vendors; for example, the LUXBEAM Lithography System sold by Visitech. Wintechdigital sells the PRO4500 with the following specifications; 5.5 Watts, 405 nm and 58 micrometers for 2500 euro's. DMD chips can handle less optical power at shorter wavelengths. For wavelengths below 405 nm, the power limit is currently 4 W per chip DLP9000UV.
  • Laser Diode (LD)
    • Used by: Manz, Envisiontec
    • Wavelengths: 405, 395, 375 nm
    • Frequency: 50 MHZ
    • Price: 22 euro's at 405 nm, 3870 euro's at 375 nm
    • Power: 0.4 W at 405 nm, 70 mW at 375 nm
    • Cooling: Air is sufficient, SLD3237VF can operate at 80 degrees.
  • Diode-Pumped Solid State Laser (DPSSL)
    • Used by: Orbotech
    • Wavelength: 355 nm
    • Frequency: 80 MHZ
    • Power: 24 W
    • Price: 190k euro's
    • Vendor: Coherent
    • Sizes: LASER 305 x 200 x 1100 mm, power supply 482 x 177 x 505 mm,
  • Nd:YAG LASER
    • Used by: 3D systems and Materialise
    • Wavelength: 355 nm
    • Power: 1 W
    • Frequency: < 1MHZ

The femtosecond laser, which can be used in two-photon polymerization to focus light in space and time and trigger a non-linear reaction, was thought to be too expensive for large-area photo-polymerization.

Physics

In the following, an analytical description of the system is given. The section starts with a parameter definition. Hereafter, the following properties are discussed; polygon, spot ,transparent parallel plate and polygon tilt angle. All the equations are also available in a Python script. This script can be used to quickly obtain the properties of the system. The calculations are verified with a numerical simulation.

Parameter Definition

The polygon rotates about its center, i.e. the point inside the polygon that is equidistant from each vertex. The substrate moves under the polygon in a certain direction. The smallest angle between the illumination direction and the substrate movement direction is defined as the polygonal tilt angle.

  • <math>\alpha</math> denotes the static polygonal tilt angle. This is 90 degrees in the Hexastorm.
  • <math>I</math> is the angle of incidence of the optical beam on the transparent polygon
  • <math>I_{max}</math> is the maximum angle of incidence used during illumination
  • <math>f_{efl}</math> is the effective focal length of the lens used to focus the bundle
  • T defines the thickness of the polygon, T is equal to 2r.
  • r defines the inradius of the polygon
  • a defines the polygon side length
  • R defines the circumradius of the polygon
  • v is the number of vertices of the polygon.
  • n is the refractive index of the polygon, quartz is used with a refractive index of 1.47
  • d is the diameter of the aspherical lens
  • <math>\lambda</math> defines the center wavelength of the laser diode beam

Polygon

Figure 6.

In figure 6, a regular convex polygon is shown with the following parameters; r is the inradius, R is the polygon circumradius and a is the polygon side length. In figure 6, the number of vertices, v, is equal to 8. Earlier, we defined 2r to be equal to T. The number of facets of the polygon has to be even for opposing planes to be parallel. If the number of facets is uneven, there will be an edge crossing during illumination which makes the polygon unsuited for scanning.

  • <math>a=T\cdot tan(\pi/v)</math>
  • <math>R=\dfrac{a}{2 \cdot sin(\pi/v)}</math>
  • The interior angle of a simple polygon with v vertices is <math>180-360/v</math> degrees.

For an octagon, <math>I_{max}=90-(180-\dfrac{360}{v}) \cdot 0.5</math> which is 22.5 degrees.

Spot

Light emerges from a small optical window from the laser diode and as a result diverges. There are several ways to focus the diverging beam. The choice is a trade-off between spot quality and cost. A laser can be focused directly with an aspherical lens. This is cheap but will give an elliptical spot. The laser cannot be tightly focused as aspheric lenses typically have a small diameter. A better spot can be obtained by first collimating the laser diode with an aspherical lens and circulating it hereafter with an anamorphic prism pair. The bundle can then be focused with an achromatic doublet. This is a more expensive solution but can give a smaller and circular spot.

Lens Alignment

The aspheric lens position accuracy is determined by the optical magnification of the whole system. The emission point typically has a size of 0.5 micrometers by 1 micrometers. The size can be measured via the Fraunhofer diffraction pattern. The emission point accuracy is assumed to be +/- 80 micrometers. This was estimated from similar laser diodes. For a 50 micrometers spot, the aspheric lens has to be placed at an accuracy of 3 micrometers. The magnification is 50. The aspheric lens can be purchased mounted with a M9 thread and screwed into position with a thumb screw mounted on the lens.

Rayleigh length

The spot is defined to be in focus in twice the Rayleigh length; <math>z_r=\dfrac{2 \pi w_0^2}{M^2 \lambda}</math>. <math>M^2</math> is called the beam quality factor. Most collimated single TE mode laser diode beams have <math>M^2</math> of 1.1 to 1.2, source Sun, Haiyin.

Spot size

The spot size of a collimated and circulated bundle focused by an achromatic doublet is <math>w_0=\dfrac{4\lambda}{\pi}\dfrac{f_{efl}}{D}</math>, where D is the diameter of the collimated bundle. The spot distance is <math>f_{efl}</math> from the achromatic doublet.

The spot distance of a laser diode directly projected by an aspheric lens is given by the thin lens equation; <math>\dfrac{1}{f_{efl}}=\dfrac{1}{s_1}+\dfrac{1}{s_2}</math>. <math>S_1</math> denotes the distance between the laser diode and the aspheric lens. <math>S_2</math> denotes the separation between the aspheric lens and the spot. The magnification, M, is given by <math>M=-\dfrac{s_2}{s_1}=\dfrac{f}{f-s_1}</math>. As the emission point is not square, the spot will be elliptical.

The smallest spot which can be formed is given by the Airy disk; <math>w_0 \approx 1.22\dfrac{s_2 \lambda}{D}</math>. Here D is the width of the collimated beam at the lens.

Transparent Parallel Plate

The properties of a parallel plate are described by Smith and Wyant. The most important properties of a parallel plate are summarized in this section. Typically, a parallel plate is used to transversely shift a collimated bundle. It can be concluded from Snell's law that the refracted bundles are parallel with the incident bundles. For a converging beam, a parallel plate also gives a longitudinal focus point displacement away from the source and optical aberrations. The optical aberrations increase if I is increased. Via an analytical calculation it is ensured that the Strehl ratio is above the Rayleigh limit at <math>I_{max}</math>. This effect starts to play a role for spots with a diameter below 30 micrometers.

Displacement

  • longitudinal displacement <math>=\dfrac{n-1}{n}T</math>
  • transversal displacement <math>=T sin I(1-\sqrt{\dfrac{1-sin^2 I}{n^2-sin^2 I}})</math> denoted as <math> \tau </math>.

The spot speed can be derived by differentiating the transversal displacement with respect to time. Let's assume the angular speed is constant, i.e. <math> \frac{\partial I}{\partial t}=c </math>. The chain rule can then be used to determine the spot speed <math> \frac{\partial \tau}{\partial t}(t)=\frac{\partial \tau}{\partial I}(I(t))\frac{\partial I}{\partial t}(t)</math>. The speed at the center is smaller than the speed at the edges of a scan line. As a result, the amplitude at the center should be smaller and is ideally corrected for by the laser diode driver by varying the pulse frequency or current.

Strehl ratio

The optical performance of the system can be evaluated via the Strehl ratio. If the Strehl ratio gets below a threshold, the aberrations will become dominant and the system will not image properly. As a result, it must be ensured via calculation that the Strehl ratio is larger than some acceptable limit, e.g. the Rayleigh limit of 0.71. Literature provides us with the Seidel coefficients of the main aberrations. These are used to determine the Strehl ratio. In the following, a quick overview is given. The f-number or <math>f_\#</math> equals <math>\dfrac{f_{efl}}{D}</math>. A transparent plate does not have a Petzval field curvature aberration. As a result, the projection of the transparent polygon is telecentric. The third order Seidel aberrations are listed below using Wyant. To simplify checking, the equations are listed with the page and equation number from James Wyant's book titled Basic Wavefront Aberration Theory for Optical Metrology.

  • spherical wavefront aberration <math>=-\dfrac{T}{f_\#^4}\dfrac{n^2-1}{128n^3}</math>, page 42, equation 72
  • coma <math>=-\dfrac{TI}{f_\#^3}\dfrac{n^2-1}{16n^3}cos\theta</math>, page 44, equation 75
  • astigmatism <math>=-\dfrac{TI}{f_\#^2}\dfrac{n^2-1}{8n^2}cos^2\theta</math>, page 45, equation 77

The coefficients can be used to calculate the optical path difference W defined on page 17.

<math> W(x_0, \rho, \theta) = \sum_{j,m.n}^{}W_{klm}x_0^k \rho l cos^m \theta</math> with <math> k=2j+m </math> and <math>l=2n+m</math>

The coefficients <math>W_{klm}</math> can be determined from the Seidel aberrations and table 2 on page 17. X is <math> \rho cos \theta </math>, for more details see Wyant.

The optical path difference can be used to calculate the wavefront error <math> \sigma </math>, see equation 62 on page 37.

<math>\sigma^2=\dfrac{1}{\pi}\int_{0}^{2\pi}\int_{0}^{1}\{\Delta W(\rho,\theta)-\Delta \overline{W}\}^2 \rho d\rho d\theta</math>

The wavefront error is converted to lambda wavefront error via division;

<math>\sigma_{\lambda}=\dfrac{\sigma}{\lambda}</math>

Finally, the Strehl ratio can be calculated with the first three terms of its Taylor series, see Wyant page 39 equation 67.

<math>\text{strehl ratio} \approx 1- (2 \pi \sigma_{\lambda})^2 + (2 \pi \sigma_{\lambda})^4/(2!) </math>

As can be seen from the equations, the Strehl ratio is minimal for <math> I </math> is <math> I_{max} </math>.

Polygon tilt angle

If a polygon is made thicker, multiple laser diodes can hit the same polygon. As can be seen in figure 7, the polygon axis must be tilted as otherwise all the laser diode projections will completely overlap each other. The polygon tilt angle can be 45 degrees if the scan length per laser is longer than the separation between two lasers. Kleo is not able to do this as the image gets distorted at the edge of a lens and the bundle exits the lens at 90 degrees. In Kleo's system, the polygon tilt angle is less than 45 degrees. This can be proved as follows. The scan length per laser is denoted as <math>S_L</math>. The scan length per laser orthogonal to the substrate movement is written as <math>y_{length}</math>.

<math>y_{length}=sin(\alpha) \cdot S_L</math>

The distance S between two subsequent lenses, i and i+1, orthogonal to the substrate movement equals

<math>y_{i+1,i}=sin(90-\alpha) \cdot S_{i+1,i}</math>

Overlap between diodes requires;

<math>y_{length} - y_{i+1,i} \geq 0 </math>

As a result, for 45 degrees we have <math>S_L \geq S_{i+1,i}</math>. This shows that Kleo cannot use 45 degrees. In the above analysis the polygon tilt angle is set equal to the tilt angle of the laser diode lanes. This is not true, in reality the angle will distort slightly due to movement. This effect is very small and has been neglected.

Figure 7.

Simulation

The equations were verified with an open optical ray tracing and lens design framework named Rayopt. Using this framework, it can be verified that the system is telecentric and the system is in focus over a plane, i.e. it has a flat field projection. The script has been made available by Hexastorm here. A picture of the output is shown in figure 8.

Figure 8.

Experiments

A CCD camera was placed under the Hexastorm. A neutral density filter was placed on top of this CCD camera. The laser was focused onto the CCD chip via the thumb screw. A single picture of a static and three pictures of a dynamic exposure are shown below. A script has been provided by Hexastorm which can be used to determine the spot size from these pictures using OpenCV. A pixel measures 4.65 by 4.65 micrometers in these pictures. The pictures are stored as bitmap to ensure analysis is still possible.

Static exposure

The static exposure of a single spot is shown in figure 9. The movement of the spot is not shown. This movement is very small but noticeable. It does not effect the resolution of the current Hexastorm.

Figure 9.

Dynamic exposure

In a dynamic exposure, the cross scan error and jitter can be determined. The jitter is the scan error in line of the scanning direction. The cross scan error is the scan error orthogonal to the laser scanning direction. In the current Hexastorm it is not possible to determine the facet. If this was possible, one could correct for a scanline shift per facet. As a result, it is important that subsequent laser lines overlay each other if the laser head is not moved. The pictures were taken at 67 revolutions per second. Two features are shown. A feature made with 2 and a feature made with 4 laser pulses at a laser frequency of 100 kHz. Early versions of the Hexastorm had a large cross scan error due to improper mounting of the polygon. This was later improved. Currently, the cross scan error is in the order of 40 micrometers. An early exposure with a large scan error is shown in figure 10. The improved version with a low cross scan error is shown in figure 11.

Figure 10.
Figure 11.

Finally, it is also possible to project only at a single facet. This improves the quality but reduces the scan line frequency to one per revolution. A picture of a single facet illumination with a hexagonal prism is shown in figure 12.

Figure 12.

The Hexastorm is very stable in the scanning direction. The polygon must be very well made to achieve overlay of multiple facets. It might be beneficial to make both the polygon axis and the polygon prism out of quartz. Similar to a reflective polygon, the prism can then be clamped instead of glued on top of the polygon base.

Additional Claims

In this section, we want to quickly list some possible applications of transparent polygon scanners to generate prior art. This list has been created to limit patent claims. These ideas, however, have not been widely tested. It has been quickly drafted to generate prior art.

LIDAR

LIDAR is a surveying method that measures the distance to a target by illuminating that target with pulsed laser light and measuring the reflected pulses with a sensor. In the following we outline how a transparent polygon scanner could be used in these systems. The transparent polygon could be used directly after the laser sources so the bundle is scanned in a second direction. This could be beneficial as it can be used to augment the resolution. Companies like Velodyne use a group of laser diode sources and sensors to increase the resolution of a laser scanner. In short, we do something similar where this group is achieved at the detector or emitter by rotating transparent polygon. An example where the emitter is enlarged with a transparent polygon is given below;

Figure 13.

The transparent polygon, aspherical lens and laser diode could also be placed horizontally or in in another position if hereafter the beam is redirected with a mirror, see figure 1 and 2. Note: in the picture the polygon and lens collide; this is a drawing error. The polygon should be placed so it can rotate.


Foil

A transfer substrate simplifies the application of a layer. Coating can be made easier with a blade which is more suitable for viscous, i.e. filled, resins. Lithoz uses a rotating disk in its LCM technology, see video. Admatec uses a foil see patent. In the past, TNO tried to patent a foil coater see EP20090164821. This most likely failed due to a patent from Charles Hull, US5637169. In any case, we do want to list a explicit example of how a foil could be used in combination with a transparent polygon scanner. The foil would be made in contact with the part during the illumination. The two images show how the foil should be applied in up projection or down projection.

Figure 14.

The rest would be very similar and easy to implement for a skilled observer, see TNO's description or Hull's description. The coating layer applied on the foil might be applied very precisely so areas are not coated twice or to block interaction between the foil and an already coated section; see figure 4. It is also straight forward to outline how this could be used in the case of multiple laser diodes. The scan head is still moved over a part. The scan head is moving relative to the part. The foil is moving however and as result the the foil and part are static with respect to each other. The foil may be made from Teflon or Teflon AF. It might also be beneficial to add a glass plate between the foil and the laser to create a flat reference substrate, see figure 15.

Figure 15.

Algorithms

The polygon facet can be detected by giving a facet a marking and detecting this marking while the polygon is rotating. This marking could be created by coating the edge of a single facet and measuring it's reflection with a second photodiode. If the facet number is known, one can correct for scan errors which are facet dependent.


Laser bundle position

Not for all lasers it might be possible to measure the laser bundle directly with a photodiode. In these cases, it might be beneficial to add a second lower power laser bundle on the same facet and in the same direction or on a different facet (for instance orthogonal to the high power beam). That position could then be monitored with a photodiode.

Immersion lithography

The smallest feature you can pattern with a light source is dependent on the wavelength. Typically the smallest feature is in the order of half the wavelength. The wavelength is dependent upon the medium the light travels trough. Companies like ASML temporarily coat the substrate with a liquid to lower the wavelength and increase the resolution, also known as immersion lithography. As such, it might be beneficial to use a similar technology in the case of transparent polygon scanner. For example a liquid could be applied on the foil shown before. This liquid would not be used to get solidified but would only be there temporarily and used to increase the resolution. Another option would be to remove the whole foil and move a transparent plate over a substrate which is coated with a liquid. A transparent polygon scanner would then illuminate through this transparent plate.

Figure 16.

Bioprinting

The Aether1 is an example of a bioprinter. The Aether uses UV light to solidify liquids during printing, see video. Currently, the UV light not only exposes photo-polymers but also the cells. The UV light damages the cells. We claim that the Hexastorm is used as an UV exposure source in a bioprinter. The Hexastorm could ensure that only the photo-polymers are exposed and not the stem cells. The printer would deposit liquid or cells with syringes and selectively expose them with the Hexastorm.

Laser sources

As alternative to a laser diode, a quantum dot laser, C02 laser or fiber laser can be used. The usage of a different laser source might be beneficial for laser cutting, printing or sintering of metal, plastic or any other sort of powders.

Carbon 3D

Carbon has a technique which it denotes as Continuous Liquid Interface Processing (CLIP). Among others, it uses a Digital Micro-mirror Device (DMD) to illuminate a surface continuously. These DMDs have a pattern/pixel rate of up to 20 kHz. Laser diodes can achieve a refresh rate up to 50 MHz. DMD's are hard to combine with laserdiodes due to multiple slit interference. At 50.000 RPM and six sides, a transparent polygon scanner exposes at line rates of 5000 Hz. In CLIP, the part concurrently advances away from the DMD projection which minimizes stair stepping and enables the production of flexible parts. With a transparent polygon scanner, the refresh rate is so much higher that it might be possible to keep the part static. If the part is kept static and the pixel information is rapidly altered, an exposure area of fluid, typically a polyurethane, can be modified as it grows towards the Teflon AF. Before the light solidifies the so called "deadzone", the scanner moves to the next area or pixel. Another option, would be to expose a full scan line multiple times and alter it as it grows toward the Teflon AF. Before the line solidifies, the so called "deadzone", the scanner moves to the next line. Finally, a combination of the above i.e. exposing a line multiple times and changing the pixel information might be option. Some more information on coating are outlined here recoating.

2D Imager

Via a transparent polygon source you can create a line from a laser spot, i.e. you can map a point (0 dimensions) onto a line (1 dimensions). Naturally, with a second transparent polygon with has its rotational axis orthogonal to the first you can map the line to a plane (2 dimensions). The second rotating prism would be thicker and typically rotate at a lower speed. This would partially mitigate the disadvantage, that it is much thicker. As a result, you form a 2D image plane. This image plane can then be translated with an optical transformer, such as a single lens

Bird control

Companies like Bird-X use lasers to scare birds at public air ports. Birds can get accustomed to the pattern and the pattern might be dependent on the type of bird. As such, it might be beneficial to alter the pattern of the laser with a transparent polygon scanner for bird prevention.

Satellite Communication

Companies like Inmarsat use laser bundles for optical communication with satellites, see video. The transparent polygon scanner can be used to transform a 0D laser spot into a 1D line or 2D plane. This plane or line can then be transformed with lenses and used to communicate with other satellites. For a DIY exapmle with a microphone and a speaker see video.

Food printing

To get microwaves meals pass the FDA, a prototype meal with egg whites is typically made. These prototype meals consist out of salt and liquid egg whites. After microwave exposure, the FDA slices the prototype meal and checks whether the exposure is good enough. These microwave meals are made by hand. The Hexastorm could expose the liquid egg white with IR radiation and trigger a maillaird reaction. If the process is combined with inkjet or needles more complicated egg white meals can be made. A layer of liquid egg white is coated an solidified with the Hexastorm. A 3D omelet can then be made by stacking multiple layers.

Tube measurement

Companies like LAP laser use reflective polygon scanners to measure tube diameters. Industrial giants like Vallourec use a combination of two of these scanners to inspect high collapse tubes. In a similar fashion, a transparent polygon scanner could be used to measure the diameters of tubes with a diameter smaller than the line length. Two transparent polygon scanners could be used to measure the diameter of larger tubes if they expose only the edges of these tubes. It must then of course be known that the tube diameter fluctuates less than the line length. So a tube with a diameter of 1000 mm can be measured if the diameter fluctuates less than e.g 10 mm.

Flexographic sleeves

The Hexastorm can be used to print flexographic sleeves directly. The current process is indirect.