open hardware fast high resolution LASER

AKA Hexastorm

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An open-hardware fast high resolution LASER suited for Printed Circuit Board (PCB) manufacturing or 3D printing. The laser head uses a prism instead of a mirror.

The goal of this project is to develop a laser head for 3D printing or PCB manufacturing which uses a scanning prism and is easy to assemble.
The open-hardware fast high resolution LASER is demonstrated by the manufacturing of PCBs. PCB is desirable from a technical point of view as it is 2D which makes exposure errors easily detectable. Cyanotype paper is used as it can be developed with water. The current electronics also provide the possibility to cut a PCB with a spindle.


Specifications were determined from the proof of concept model by exposure onto a camera without lens and OpenCV

  • wavelength: 405 nm
  • rotation frequency:  up to 21000 RPM, current 2400 RPM
  • line speed: up to 34 meters per min @ 21000 RPM
  • spot size FWHM: circular, 25  micrometers diameter
  • cross scanner error: 40 micrometers  (error orthogonal to scanline)
  • stabilization accuracy scanning direction :  2.2 micrometers (disabling/enabling scanhead)
  • jitter: 35 microns (error parallel to scanline)
  • laser driver frequency: 2.6 MHz
  • maximum scan line length: 24 mm
  • typical scan line length: 8 mm
  • optical power: 500 mW
  • facets: prism has 4 facets


If users desire an FPGA, they can extend the Beaglebone with for example the Beaglewire.

  • Beaglebone green
  • Firestarter cape  (laser driver, 3x TMC2130 stepper drivers, PWM spindle and fan control)


An image can be uploaded to the scanner and exposed on a substrate. An exposure result on cyanotype paper is shown below.
Resolution looks to be around 100 microns. Stitching still needs to be fixed, results in white lanes.
The idea is that throughholes are made with a spindle.  There is a project on Hackaday where a PCB is cut with an EDM. There is quite a lot of documentation and code available but it does contain mistakes and can be hard to interpret as it is in development. The project has limited peer review. Readers are invited to step forward if they have objections or questions with the claims made.

An exposure goes as follows (for the result see above).

Hexastorm fork of LDGraphy
Hexastorm fork of BeagleG
Optical design
old FPGA code

PCB design

Hardware designs
CAD files
Cartesian frame was donated by FELIXprinters.

Literature Research
White paper @ Reprap

Other Links
Official website
Failed kickstarter campaign

Adobe Portable Document Format - 5.57 MB - 06/13/2019 at 07:28


calibration data of current scanhead

Zip Archive - 278.28 kB - 01/25/2019 at 18:50



measurements and algorithm used to determine stabilization accuracy, see blog

RAR Archive - 594.17 kB - 01/25/2019 at 14:50



bom ofthe old firestarter and overview of layout. This board is no longer in use.

Adobe Portable Document Format - 912.66 kB - 05/07/2018 at 21:30


  • 1 × Quartz optical window, 2mm thick, 30x30 mm
  • 1 × Beaglebone Green
  • 1 × BPW34-B (photodiode)
  • 1 × Heavy Duty Heatsink / Laser Diode Housing for 5.6 mm with Fan
  • 1 × BDR-S06J 405nm, 500-600mW Blue-violet Cut-pin Laser Diode

View all 11 components

  • SX10: wide scan angles with prisms

    Hexastorm7 days ago 0 comments

    I have found a commercial prism scanner in the field; the Trimble SX10 scanning total station.

    For more details see this  article on the big eye. They translate light by refracting it through two orthogonal prisms and then collimate it with a lens. The trick here is that they use it to scan over a wide angle, instead of  short angle. They have a sort of reverted setup.

    You can see they start from a point and then form a collimated, aka parallel, bundle.
    It turns out that this design was used in the AGA Thermovision System 680 in 1970.

    The challenge solved by this thermal imaging camera was how to scan [over a wide area] using a single, very expensive, and liquid nitrogen cooled infrared detector. The solution was to pass the beam through two rotating [octagonal] germanium prisms, one horizontal and one vertical.
    A picture is provided on page 114 from inverse problems in engineering mechanics.

    The germanium prism is shown here.

  • Current state

    Hexastorm08/10/2019 at 15:04 0 comments

    Changed the scanner and ported all designs to FreeCad. The scanner can be calibrated via set screws.
    The scan head passes all tests; laser can be turned on, polygon rotates and the photo diode can be read out via the circuit.

  • Hexastorm featured at Fabbaloo and trending on Hacker News

    Hexastorm08/05/2019 at 11:17 0 comments

    Hexastorm got featured at Fabbaloo, a well known 3D printing blog.

    As such, I posted it on Hacker news and was able to get a lot of traffic to my video from there!

  • Assembled boards

    Hexastorm07/31/2019 at 12:27 0 comments

    I have assembled the boards. The results are shown below;

    front main board of laser module

    back main board of laser module

    front cape of beaglebone

    front photo-diode board (photodiode in the wrong position bar should be right... not left)

  • Updated Boards

    Hexastorm07/22/2019 at 11:57 0 comments

    I have made three PCBs; beaglebone cape, laser module pcb, end of stopline pcb.
    This should have the following advantages;

    1.  Photodiode is read out with amp and Schmith trigger
    2.  Laser scan head can easily be detached from machine
    3.  Electrical wiring to the laser are kept short. The anode and kathode of the laserdiode are not exposed outside of the scan head. Damage is prevented and electrical noise minimized.
    4. The scanhead is a separate entity from the cape. The scanhead could be interfaced by other boards.  The scanhead can also be detached to place it into a different setup.

    The Beaglebone cape is shown below. The main board can be connected to three stepper boards, three endstops, the spindle controller and the scanhead via a 10 pin cable.

    The Beaglebone cape talks to the scanhead via 10 pins. The scanhead also needs three power lines. The power is provided via the Firestarter cape as there are some safety measures present there.

    The scanhead board has two sides in and out, so one can connect to the components in the scan head.

    The PCB for the for the photo-diode with the op amp and the Schmitt trigger is shown below

    Boards are submitted for order via PCB way. Total costs for 3x 5 boards plus shipping is 38 dollars.

  • Printing with droplets

    Hexastorm07/16/2019 at 12:45 0 comments

    Let's quickly read, Inkjet Technolgy for Digital Fabrication, IAN M. Hutchings. There are various ways to create droplets such as Continuous Inkjet and Drop On Demand (DOD).
    A well known challenge with DOD technologies are the limits with respect to viscosity.  Continuous inkjet allows for higher viscosity but the stream has to be broken up into droplets and droplets need to be selected.
    In Continuous Inkjet generation an electric field can be used to position the droplets, see Sweet 1965.
    Rejected droplets can be put in a container and reused.
    This requires a conductive ink. For non-conductive inks, Kodak has explored alternative selection techniques to select the droplets via air. A patent on droplet selection can be found here US8544974.
    The liquid stream has to be forced to break up into droplets when the liquid stream leaves the nozzle. As man, you might recall from peeing that the stream doesn't break up into droplets immediately when the liquid leaves the nozzle.
    A way for doing this is via a piezoelectric effect or heating.  The droplets can be detected by a stroboscope and a camera.
    I claim that the Hexastorm is used to force the break up of droplets in a continuous inkjet head using heating. I claim that the Hexastorm is used to detect the position of one or more droplets.
    I then claim that the Hexastorm is used as a selection mechanism to evaporate certain droplets or push them away by colliding them with another droplet generated with laser induced forward transfer.
    I claim that the Hexastorm is used to emit a droplet from one stream via LIFT and then merge it into another droplet.
    Likewise, I claim the same things for a drop on demand system where droplets are ejected by acoustic energy, piezoelectric effect or thermal effect. Again the Hexastorm can be used to detect the position of droplets, see if nozzles are clogged and calibrate the inkjet head by checking the position of droplets either upon the substrate or in the air.
    Light can be used to cure liquids so they become conductive via so called flash curing. In some novel conductive inks nano-particles are dissolved. The solvent is used to lower the viscosity and facilitate transportation in the head. If the ink is on the substrate, the solvent must be removed which is done via flash curing.
    They could also cure UV inks and vary the dosage per ink using optical coherence tomography. Or use OCT to check wether the conductive ink is fully cured.

    Anyway, what might be of interest to the reader is the work of Georg von Hippel from the MIT Sloan school of Management.

    At the moment, l I am a bit done with creating prior art and will move back to building the scanner!

    People who think I am over doing it with the claims should read about the patent war between formlabs and DWS. Basically, DWS patented the idea of heating a liquid in a bottom up projection photo-polymer printer. I agree with Formlabs this is not novel at all but also agree with DWS that this is a typical 3D printing patent. Stratasys has a very similar patent on a heating build chamber for fused filament printers.

  • Generating prior art with patents

    Hexastorm07/15/2019 at 18:21 0 comments

    Prior art is of huge importance to the open-hardware movement. It prevents that certain markets become locked for 20 years by patent law.

    Let's generate some prior art with patents. I claim all the claims generated by rewriting all patents in the world which use the concept of scanning mirror and do not mention the concept of scanning prism. I make these claims by rewriting the scanning mirror patent but now using the concept of scanning prism. I think these new claims would be obvious for a Person Having Ordinary Skill in the Art (PHOSITA), familiar with my work and familiar with the patent. The total of these claims and other prior art describe the legal application limits of transparent polygon scanning.

    Let's provide some examples;

    Example 1: US7892474

    This is an interesting patent it describes something like Continuous 3D printing. Could explain why Carbon didn't outline the figure 3 option.

    Claim 1 reads  "... comprising the step of solidifying a photo-polymerizable material by means of mask exposure of a build area or partial build area in a building plane via electromagnetic radiation from a digital light processing/digital micromirror device projection system ..."

    using transparent prism creates prior art not under patent let's reformulate

    "... comprising the step of solidifying a photo-polymerizable material by means of refraction exposure of a build area or partial build area in a building plane via electromagnetic radiation from a transparent polygon scanner device projection system ..."

    Example 2: US9079355B2

    The first reflective polygon scanner in photo-polymerization was described by the Institute of Physical and Chemical Research (RIKEN) in 1997. 
    RIKEN did, however, not describe the combination of a laser diode and reflective polygon scanner.
    Shuji Nakamura of Nichia discribed the blue diode laser in 1996.  Envisitontec patented the combination of polygon scanner, laser diode and 3D printing in 2011. This was a smart legal move.

    Claim 1 reads:

     "... and deactivatable ultraviolet laser diode and a rotating polygonal mirror ..." 

    using transparent prism creates prior art not under patent let's reformulate

    " ... and deactivatable ultraviolet laser diode and a tranparent polygon scanner ..."

    Example 3:  EP3233499B1

    Laser induced forward transfer can be used to generate droplets with laser light. The earliest description I could find date back to 2004.
    Poeitis patented this process for bio-printing in 2015. In this video, it is describes how laser-assisted bioprinting works.  The process is also shown in figure 1 and 2 of the patent.
    From the video it can be concluded that a transparent polygon scanner can be used to shoot with a laser pulse on a disk so a droplet is emitted. This can be used in bioprinting, 3D printing or used in the semiconductor industry to deposit resist,  glue, polymer or ink etc.
    A microfluidic chips with multiple channels could be made and the transparent polygon could be used to send a laser pulse to the disk and  select the channel from which the droplet is emitted.

    Example 4:  US900887
    Compact, low dispersion, and...

    Read more »

  • Glass tubes and laser scanning

    Hexastorm07/13/2019 at 10:09 0 comments

    UV Light can be used to disinfect the material flowing in tubes. Infrared laser light can be used to heat specific particles/cells/droplets if the tube is made from glass. Here is a market report on UV disinfection equipment. A company active in UV disinfection is  uvo3. Transparent polygon scanning can be used in vibrometery, which can be used to measure fluid flows in glass tubes using laser doppler velocimetry. Laser galvo scanning interferometry can be used for flow velocity measurements through disturbing interfaces. Likewise a transparent polygon scanner can be used to measure flow in chemical processes.

    Ideally, the glass tube is square to minimize a lensing effect.

    Furthermore, an interesting option would to polymerize particles in the tube, or sintering takes place in the tube.  MIT patented this process in US7709554, but used a DMD projector and not a transparent polygon scanner. In addition, I claim the case the walls of the tube are created from Teflon AF. This could for instance done on a micro-fluidic chip which would again be produced by a transparent polygon scanner. One could simply use the setup outlined here and use a transparent polygon instead of a galvo scanner. If this is not sufficient I would make the tube square and sufficient porous by laser engraving the tube with a transparent polygon scanner and  C02 laser, where i spin the prism at a relatively low speed and possibly use an auxiliary bundle to fix the timing.

    The speckle pattern can be measured which is created by shining in the tube. This process can for example be is used in the food industry to measure the dairy viscosity in a glass tube. You could walk around in the garden with a handheld Hexastorm and measure the biological status of a plant.
    The detector could be a CCD/CMOS camera at the same side or opposite side of the plant leaf or glass tube. Possibly, the transparent polygon scanner is under an angle so the reflected light does not fully transmit back to the polygon scanner but can be measured by another device at the same edge of the tube, like a CMOS/CCD chip/grating light valve with appropriate lens.

    The laser is pulsed and the time of flight is measured. This allows one to both record the amplitude and time phase spectrum of the material under measurement.  Incidentally, I claim that gasses are flowing in the tubes or that that tracers are applied to the particles in the tube.

  • 3D Glasses

    Hexastorm07/12/2019 at 18:31 0 comments

    In my previous post, I outlined how a transparent polygon scanner can be used for detecting eye diseases.

    Logically, a transparent polygon scanner can also be used in 3D glasses.  Reflective polygon scanners are used for creating a screen in a laser TV.

    A lot of companies are active in 3D glasses; e.g. Google Glass, Magic Leap, Oculus and Hololens.

    Colors are created in a laser TV by  coupling three lasers of different wavelength and optical power in the same bundle.

    For 1080p at 100 hertz. you would like something on the order of 100,000 lines per second.

    At 30.000 RPM and 8 sides prism you have 4000 lines per second.

    This is not enough;

    Option 1:  Miniaturization
    Scale down the size of the prism, this will make it easier to spin it at high speed. The angular momentum drops due to lower mass and radius, which implies lower energies at a fixed RPM. The fastest spinning disk ever made at 600 million RPM is also small.

    Option 2: Fiber array
    You could use 20 fibers where each fiber has 3 lasers but once you have multiple lasers per color, then you have to get everything very precisely aligned with 6 degrees of freedom. This is a tough problem with just 3 colors. Let alone 20 fibers with 3 laser colors.

    Option 3: Increase the number of facets
    There are prism which have 72 facets and can be spun at 70.000 rpm  (see roadrunner).

    Option 4:  Optical transformation
    Project 1920x1080x100 pixels but divide it over 4000 lines where each line has 51840 pixels. This would however require a small spot for a 20 mm long line  of something like 385 nm which seems unfeasible

    In summary, the problem seems quite hard. A polygon would be needed that can be spun at say 750000 rpm. The second in the other direction can then be created by a second prism.

  • OCT: Transparent polygon scanning in Ophthalmology

    Hexastorm07/12/2019 at 12:30 0 comments

    In the following, I would like to outline how transparent polygon scanning can be used to save lives. I again aim to create prior art to extend the freedom of use of transparent polygon scanning. 

    Figure 2 (from Wikipedia).

    Typical optical setup of single point OCT. Scanning the light beam on the sample enables non-invasive cross-sectional imaging up to 3 mm in depth with micrometer resolution

    Optical Coherence Tomography (OCT) is an imaging technique that uses low-coherence light to measure samples based upon the principle of light interference. It is used in the medical industry to detect cancer in tissues and diseases in eyes, e.g. the Cylite of Hewlett Packard. OCT is typically used to obtain information from a sample. In 3D printing it has been used to verify a print. For example, Photoncontrol used Optical Coherence Tomography and Raman spectroscopy to test the quality of bio-printed tissue, see 1. A startup, called Inkbit from MIT, is using it to create samples accurately. They print droplets with an inkjet head and then verify the position of these droplets using among others OCT.
    OCT has also been used to detect the adhesion between layers in a 3D printing process, see Non-destructive testing of layer-to-layer fusion of a 3D print using ultrahigh resolution optical coherence tomography.
    Due to the interest in this area, I decided to elaborate upon how OCT can be used in combination with a transparent polygon scanner. I claim that in figure 2 a transparent polygon scanner is used instead of a galvo scanner. I claim that in the optical path of the Hexastorm a beam splitter is placed after the aspherical lens and before the first cylindrical lens to enable the scanner for optical coherence tomography. I claim the use of a transparent polygon scanner for wavefront measurement in Ophthalmology and Optometry. The vertical measure of an eye ball, generally less than the horizontal, is about 24 mm. The current scan head has a scanline of maximum 24 mm, making it already close to dimensions required for eye ball measurement. I claim that possibly two transparent polygon scanners are used in ophthalmology and optometry, to move the bundle in two directions.
    An OCT enabled transparent polygon scanner might also be useful for 3D printing. Imagine that a small percentage of the bundle is scattered to the reference mirror and most of it used to go to the sample. It will then be possible to sinter powders or polymerize liquids at the sample location. A small portion of the beam will be reflected and refract back to the beam splitter and interfere with the reference beam at the photo-detector.
    This allows one to measure the photo-polymerization or sintering process during printing. I can imagine this is especially useful if the layer height is less than the wavelength. I can also imagine that this is useful during a process akin to Hexaforming (see previous post). A hand held device could be used to check the skin of a patient. An application would be laser surgery, such as eye surgery (Carl Zeiss Meditech) or tattoo removal and laser hair removal.
    The transparent polygon scanner could also be useful in a Raman microscope as galvo's are used by NanoPhoton. In two-photon point-scanning microscopy,temporal focussing can be used to increase the image rate for a transparent polygon scanner similar to a galvo setup. Another option is in vivo imaging with HiLo microscropy but then a transparent polygon scanner.  Further possibility is Field-portable quantitive lenssless microscopy based on translated speckle illumation on sub-sampled ptychographic phase retrieve using a transparent polygon scanner.   Or A New Method of Creating High-Temperature Speckle Patterns and Its Application in the Determination of the High-Temperature Mechanical Properties of Metals with a transparent polygon scanner.
    Another option is laser scanning fluorence microscopy with a transparent polygon...

    Read more »

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Robert Mateja wrote 07/31/2019 at 11:48 point

Congratulations on winning Hackaday Prize 2019!  (at least in my opinion)

  Are you sure? yes | no

Hexastorm wrote 08/01/2019 at 09:30 point

Robert, thank you for supporting me! Winning the prize would be amazing.  My current target is to get other people to try out the technology, I am really trying to make it more accessible. I hope I can show an improved prototype of the scan head soon.

  Are you sure? yes | no

Conny G wrote 05/27/2019 at 12:36 point

What material is the prism made from? How is it manufactured?
Can i make it in my "maker lab"?

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Hexastorm wrote 05/29/2019 at 11:39 point

Prism has the following properties; 2 mm thick, 30x30 mm square,  faces 60/40 < 5 arc min, chamfers 0.10 – 0.30mm, edges Polished 60/40, top bottom polished 60/40.   You will have to discuss details with manufacturers in China over Alibaba. I made the first in a maker styled lab, so yes it can be done. 

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Gravis wrote 02/03/2019 at 19:16 point

I'm also interested in the possibility of using a motor from a hard disk drive instead of a breaking down a polygon motor.  HDD motors are cheap to buy and (as I understand it,) contain an encoder and have screw holes which makes affixing things easier.

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Hexastorm wrote 02/04/2019 at 08:48 point

HDD seem too slow.  They typically spin at 5400 or 7200 RPM.  At the moment, I can go up to 24000 RPM with polygon motor. For some applications, I would like 50000 RPM or 70.000 RPM, like the roadrunner sold by precision laser scanner. Also the motors are not too expensive, they are like 20 euros. I understand 20 euro's can still be a lot but if you look at total costs; you can better pay attention to other components.

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Gravis wrote 02/05/2019 at 06:00 point

Oh, I had no idea you were planning on high speed.  Where can you get the motors in the 20 euros range?

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Hexastorm wrote 02/06/2019 at 13:40 point

You can find polygon motors at alibaba ( .  The system is a proof of concept; for desktop PCB prototyping 2400 RPM is fine. If you plan to compete with Kleo . You will need at least 50K RPM.  An option would be to encase the prism and remove the air. This will reduce the drag. You could also fill the encasing with Helium as it has low drag and a high thermal conductivity.  Like the roadrunner the encasing windows would be tilted out of plane to minimize back reflections, see

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Gravis wrote 02/03/2019 at 15:57 point

My suggestion for this project is to isolate the scanner from the 3 axis robot part so that the scanner could be made into a tool that can be changed out.  I would also ditch using BB's PRU and instead use a dedicated chip (and maybe a RAM buffer) and connect it via CAN bus.

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Hexastorm wrote 02/04/2019 at 08:58 point

I intend to isolate the scanner, and design it for specific machines. I like the idea of having a dedicated chip. In the past I used a FPGA (Xula-LX25) with RAM as  bufffer. I can imagine there are even better options. The problem is that developing a dedicated board costs time, money and a lot of experience. Zeller made a very accessible code for the Beaglebone, so I went with that. You are looking at a proof of concept. It's a technology demonstrator. Anyway if you have recommendations; or some example code; feel free to share. 

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Gravis wrote 02/05/2019 at 07:48 point

Considering this is a project where accurate timing is vital, I think an XMOS processor (e.g. XS1-L4A) would be a good fit.  Each 100MIPS processing unit is 100% deterministic with fast GPIOs.  I don't know the rate of data throughput you need but it may be easier to just cache to workload on a local FLASH chip than stream it.

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Hexastorm wrote 02/05/2019 at 10:53 point

XS1-L4A is nice... but I rather like something with lot of support and examples... probably first gonna optimize the current code and balance my prism.

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Gravis wrote 02/05/2019 at 20:37 point

XMOS stuff actually does have lot of support (, examples ( and even an IDE but I somehow missed the part where you wrote that didn't want to build a custom board.  Sorry about that.  XMOS chips make it easy to glue things together since it's 99% software so it doesn't take too much skill to make a board with them.  Consider enlisting help to make a board as there is a good chance it will alleviate timing related issues.  Good luck! :)

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Paul wrote 11/05/2017 at 03:49 point

You've certainly done your homework very thoroughly, and I see that in your application with very small optical cone angles (large focal ratio), the optical aberrations and field curvature appear to be tolerable.  That's great.

One question: You say that previous scan techniques require a large (and therefore expensive, you argue) f-theta lens, which must have one dimension at least as wide as the scan line.  In your approach, your polygons must be larger than the scan line length, but in *two* dimensions, making the volume of your optical element much larger.  Since either shape would use identical materials and fabrication processes in volume production (i.e. injection molding), one would naively expect the smaller element (the f-theta lens) to be cheaper.   How is this line of reasoning flawed?

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Hexastorm wrote 11/05/2017 at 10:51 point

A telecentric f-theta lens requires one dimension at least as wide as the scan line. A non-telecentric f-theta lens does not require that.  In my approach, the polygon must have one dimension longer than the scan line. The second dimension is 2 mm. An f-theta lens consists out of multiple lens elements, e.g. a 3 element f-theta lens. These elements have curved surfaces. The prism consists out of a single element with a flat surface. You can't make the f-theta lens out of plastic, so you would have to injection mold quartz. I am unfamiliar with the prizes for that. Besides most likely a higher price and the fact you have to use multiple elements, you also need to worry about patents. Envisiontec patented the usage of reflective polygons; US 9079355 B2 . Finally, you need a thick reflective polygon as thick polygons can deflect collimated bundles with a large diameter and these can be focused to smaller spots.  A transparent prism uses a focused bundle and therefore typically can be thinner, which keeps the price of the bearing lower.

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Paul wrote 11/05/2017 at 15:55 point

You have clearly thought about this a great deal, and have your arguments worked out well.

I wasn't considering that you might be requiring quartz.  I would have guessed even BK7 would be overkill for this application.

I mention injection molding because I look around my offices and see several laser printers.  Each of them contain a laser scanning unit with a rotating (reflective) polygon and a f-theta lens arrangement, with the final element being very large (>200 mm long).  All the optical elements of the ones I have inspected appear to be injection-molded PMMA or similar plastic.  The entire laser scanning unit must cost considerably less than $50, given the prices of the printers (all less than $200, two less than $70).  Granted, these are produced in huge volumes, but they serve as existence proof that these scanning systems with large optical elements are not intrinsically costly.

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Hexastorm wrote 11/05/2017 at 16:52 point

PMMA absorbs light at 405 nm. The laser printers at your office use 800 nm and low power lasers. I use 405 nm and high power lasers. So yes; there is concrete proof that PMMA injection molded systems are not intrinsically costly. There is no proof that quartz systems are not intrinsically costly.  It's unclear what the prices of these systems would be .

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Paul wrote 11/03/2017 at 13:21 point

A good variation on the usual way.  I build a few instruments based on this and similar methods between 1985-1989.  A couple of important notes:  

1. The scanned field is NOT flat: The optical distance to the target plane *increases* as the polygon rotates away from normal.  Not only is it geometrically longer, some of the increased  path length is in the high-index polygon too, increasing the path length even more.  The result is a curved focal or scan plane.  One of my instruments actually depended on this: a rotating polygon was used to tune the optical path length inside an optical resonator cavity, to adjust a tunable laser that was phase-locked to that cavity. 

2. You get some significant spherical aberration when you focus through a thick window like that, for similar reasons: the light rays at the periphery of the optical cone take a longer path to the target plane than rays going through the middle of the cone, with the result that they focus at a different depth.  For a laser at f/50 (or whatever it is), this probably isn't significant, but in an imaging system at f/2, it seriously degrades focus. 

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Hexastorm wrote 11/04/2017 at 22:09 point

Paul, thank you for your reply!
A transparent polygon scanner with a single laser bundle was first patented by Lindberg in 1962.  The scan field is not flat and you can get some significant optical aberrations. A full numerical model is available here . A description of this model is available in the technical presentation. The result shows that in practice the scan field is flat and the optical aberrations are not significant.

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Hexastorm wrote 11/03/2017 at 11:58 point

Well this is the first comment! If Hackers are interested in transparent polygon scanning let me know :P ..

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