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prism laser scanner

bringing additive manufacturing to the next level

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An open hardware fast high resolution LASER suited for Printed Circuit Board (PCB) manufacturing or 3D printing. The laser head can be used to write to a substrate. I am working on reading from a substrate.

The goal of this project is to develop a laser head for 3D printing or PCB manufacturing which uses a rotating prism and is easy to assemble.
Cyanotype paper is currently used as it can be developed with water.

Specifications

Specifications are determined by exposure onto a camera without lens and OpenCV. More technical details are available in the whitepaper or the business case pitch.

  • wavelength: 405 nm
  • rotation frequency:  up to 21000 RPM, current 2400 RPM
  • line speed: up to 34 meters per second @ 21000 RPM
  • spot size FWHM: circular, 25 micrometers diameter
  • cross scanner error: 40 micrometers  (error orthogonal to scan line)
  • stabilization accuracy scanning direction:  2.2 micrometers (disabling/enabling scan head)
  • jitter: 35 microns (error parallel to scan line)
  • duty cycle: 47%
  • 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
  • prism dimensions: 30x30x2 mm

Electronics

  • FPGA ICE40UP5K-SG48 with Icestorm toolchain
  • Firestarter cape  (laser driver, 3x TMC2130 stepper drivers, PWM spindle and fan control)
  • Raspberry 4

Status

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 is between lanes is quite good, see below.
Exposure below is done without cylinder lenses.

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

Acknowledgement
Special thanks go to Henner Zeller for his work on LDGraphy. The electronics and software in this project helped me a lot with constructing the laser scanner, see video.
The initial idea of using prism for laser scanning originates from Dr. Jacobus Jamar. This system uses a plurality of laser bundles in a thicker prism under an angle.  TNO, a research institute of the Netherlands, still pursues this idea, in an entity known as Amsystems.
The current gateware relies on Nmigen and some components from Luna. This is the work of white-quark and ktemkin.

Software
Hexastorm fork of LDGraphy
Optical design
old FPGA code

Electronics
PCB design

Hardware designs
CAD files
Cartesian frame was donated by FELIXprinters.

Literature Research
White paper @ Reprap

Other Links
Official website

pitchdeck.pdf

New pitch deck of 16-9-2021, also available as video on Youtube.

Adobe Portable Document Format - 2.03 MB - 09/16/2021 at 17:50

Preview
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analysts_presentation.pdf

Pitch intended for analysts who want to get a brief overview of the key markets prism scanning will disrupt.

Adobe Portable Document Format - 781.75 kB - 09/24/2019 at 08:39

Preview
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pcb_scanheadfixed.pdf

schema of the pcb for the scanhead

Adobe Portable Document Format - 45.07 kB - 09/23/2019 at 13:51

Preview
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bomlist.ods

bill of materials for the photodiode detector

spreadsheet - 13.26 kB - 09/23/2019 at 13:33

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scanheadpcb_bom.ods

bill of materials for the scanhead pcb

spreadsheet - 13.04 kB - 09/23/2019 at 13:33

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View all 9 files

  • 1 × prism, 30x30x2 mm edges parallel to < 1 arc minute 40pcs @ 20 euro per piece @ ebetteroptics
  • 1 × Raspberry Pi 3B / 4 with 16GB sd card at least 35 euro's + 9 euro
  • 1 × Brass Laser Module Housing for 5.6mm TO-18 LD 5 euro
  • 1 × BDR-S06J 405nm / Nichia S06J 405nm 22 euro (eBay)
  • 1 × 10x10x1 first surface PMMA mirror 2.5 euro per 20 aliexpress (alternative edmund optics #45-517 18 euro per 10 including shipping)

View all 12 components

  • PCB motors

    Hexastorm2 days ago 1 comment

    I converted Carl Bugeja's boards to Kicad. I used his version 3 motor as starting design. I hope to have results in 3 weeks.
    Five motor boards cost around 100 USD, so it could be interesting to try to print these boards with my prism technology.
    I did print some boards but still need to optimize my chemical process.
    I plan to place the prism on the other side of the motor board, shown below. The motor is driven using the star configuration.
    The J1 connector, connects the three phases of this motor. The J2 connector is linked to a hall sensor which measures the magnetic field and can be used to determine RPM.

    I plan to do the control with the FPGA, Carl bugeja used a microcontroller which I removed. The board can connect directly to my FPGA base board. The motor board (shown above) also has a base board, shown below. On it is a brushless motor driver U1). The hallsensor is connected directly to J2 which connects to my FPGA base board (not shown).
    I think chances are high it will work. It would really simplify the design of my product and reduce form factor.  Let's see Gravis.. if prisms and pcb motors get a long easy.
    Design can be downloaded here https://github.com/hstarmans/firestarter/tree/master/prism-motor/

    I will try to add a simulation of the physics, might do some trials with pyleecan.

  • Closeup

    Hexastorm11/17/2021 at 11:07 1 comment

    Gravis closeup is below; 3 mil is 75 microns and 4 mil is 100 microns.  I think I can still do better if I finetune and optimize development process. Also this paper is not really intented for this type of lithography.

  • New lane alignment

    Hexastorm11/16/2021 at 17:45 2 comments

    New alignment between lanes is shown below;

      I have assumed backlash is zero
      The width of a scanline is 5.54 mm, still I use 5.4 mm in reality, to achieve stitching.

    Results look pretty good. Should be more than sufficient for PCBs.

  • New laserhead exposure

    Hexastorm11/12/2021 at 17:19 0 comments

    Results look good even without cylinder lenses. Simply by improving the head and the prism a lot of issues got fixed.

    Exposure result is shown below. You can see the text hexastorm printed which looks quite sharp.

  • PCB motor

    Hexastorm11/04/2021 at 15:38 0 comments

    Gravis asked my opinion on using a PCB motor with a prism.

    In short, it seems possible to spin a prism with this motor but the prism most likely needs to be smaller.
    This motor has a diameter of 15 mm,  my prism a diameter of 30 mm. Of course, prism dimension can be changed.
    The prism can be placed in a low drag gas like helium. So far Carl seems to focus on torque and speed, an important quality for me is actually planarity. How planar is the rotation? At 5 minute 43, he shows the side ways wobble of his amazing device. This kind of wobble is undesirable and would require a cylinder pair to filter it out. This increases price which kills the low cost advantage of the motor.
    Small prisms are desirable for high accuracy applications.

    I would try to create a digital twin, this would greatly improve understanding.
    Options I see

                 - Magpy Lib: should be easy for a quick experiment

                - Pyleecan: geared to motors but does not have example of this exotic geometry

                  -      Elmer Fem , can be linked with open foam, probably too advanced and not suited
                                              for exploring the problem                        

      would make the board in kicad and not altium. An interesting script i found is (given above see hackster link). It think @carlbugeja did amazing work. For the time being, I will focus on other challenges; i.e. making the tech reliable.

  • BLDC motor

    Hexastorm10/31/2021 at 10:08 2 comments

    The prism scanner uses a BrushLess DC (BLDC) motor to spin the rotor.

    How stators are winded can be seen in this video from Nide Group.

    The BLDC external armature fusing machine is used for spot welding the wire and terminal of the BLDC rotor

    I consider to simply buy these stators and pick and placing them on my own PCBs. It would simplify the wiring a lot and allow me to compress the technology further.

    You can see the front and back of the motor pcb below. Note, that I use the NCB3111 and these are back in stock.
    I managed to find a new supplier so this is no longer an issue.

    Copying this PCB in KiCad seems a trivial undertaking.

    The back of the PCB can be seen below. The PCB is alluminum to simplify the transfer of heat.  If the rotor is spin at too low speeds the board overheats and shuts it self down. A brass standoff seems to be pressed in the board from below and secured with a plastic ring. The hole on the right is for a plastic safety thing to fixate the rotor.

    The rotor look as follows. You are looking at the bottom and can see the magnet. You can also "barely" see the six edges of the mirror.  Here is video of making a similar DIY electric motor.

  • Storing and Reading Information in Mixtures of Fluorescent Molecules

    Hexastorm10/31/2021 at 09:37 0 comments

    Came across this freely available article, basically information is stored efficiently by using color droplets.
    The method should require less energy and encoding should be more efficient as there are more options than black and white (binary).

    Links with prism scanning are as follows; droplets can be placed on the substrate using laser induced forward transfer and reading the information using hyper spectral imaging and laser microscope, see hyper spectral chips from imec.
    Researchers so far used inkjet printing and a conventional microscope.
    Security is also not mentioned in the article but it could be an interesting method to place a hidden finger print.

  • New build

    Hexastorm10/27/2021 at 16:39 2 comments




    Feel free to fork https://github.com/hstarmans/hexastorm_design

    I will post a making off video soon.

  • GreetZ to : #nmigen , #kicad, #freecad, #ldgraphy

    Hexastorm10/22/2021 at 13:34 2 comments

    The minimum viable product is completely made out of PCBs. To show my gratitude to the open-source community I added the logos of a couple projects I use to the laser head.  Source code is available here.

  • Measurements New prism

    Hexastorm10/04/2021 at 15:50 4 comments

    Cross scan error of new prism with 1 arcminutes parallelism is shown below.
    A pixel in the image is 3 micron and the distance between lines is 111 microns.

    Deviation angle of prism is
    Orthogonal wobble is;

    A deviation of approx 0.1 mm is observed at distance, d, of 30 mm from prism, which implies planes are not planar within 9.8 arcminutes.
    New prisms reduce the cross scan error. The prisms are leveled within 1 micron prior to rotation and sides should be planar at 1 arc minutes (this is guaranteed by supplier)
    To ascertain the motor is the cause, one could monitor the height deviation of the prism while rotating using a laser distance sensor.
    Another option is to think about the results with the cylindical lenses.
    If it is assumed the prism is perfectly planar, the refracted rays remain parallel with the incident rays. The second cylindrical lens maps all parallel rays with the same angle to the same point in the focal plane. Ergo it filters any issues with the motor.

    Use of cylindrical lenses proved to be highly beneficial, which implies these problems exist.

    If higher accuracy is desired it can be resolved by;
     - using only a single facet
     - reducing the distance between the prism and the exposure plane
     - adding a cylindrical lens pair; this circularizes the laser bundle
       and filters out problems caused by rotation.

    I will look at the motor in the next post.

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Discussions

Hexastorm wrote 12/30/2019 at 15:53 point

No it wouldn't work.. you need edges polished, not the top and the bottom.
I am not shipping out prism at the moment as they r not balanced yet (working on this). I am also working on a FPGA toolchain, will post an update on my progress here soon.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/27/2019 at 04:56 point

Can you recommend a specific polygon motor module on alibaba? I don't know if there are any differences and I'd like to order one. THanks!

  Are you sure? yes | no

Hexastorm wrote 10/27/2019 at 13:37 point

Yes, you should buy exactly this motor https://nl.aliexpress.com/item/32824649951.html . It uses the NBC3111 chip. I had problems with other motors. Make sure you buy at least 2, although they are quite hard to break.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/23/2019 at 21:59 point

Dude, this is some pretty awesome work. I'd love to help refine some of the manufacturing and board designs, let me know how I can best help

  Are you sure? yes | no

Hexastorm wrote 10/24/2019 at 17:55 point

Thanks! There are two other people who have shown interest. I need at least 10 people to do a run as I have to buy the prisms in bulk. Turn around time would be significant. Producing the prism takes at least a month.
I am fixing the low hanging fruits at the moment. It is hard to help with these as you don't have a laser head. I am building a new one but there is still only one in the world :-).
Things you could look in to;

- a better alignment system for the laser; this uses four screws and is over dimensioned --> see my free cad design files

- a better alignment system for the cylinder lenses; the screw system is not really comfortable --> see my freecad design files

-  how do i put my state machine on an fpga; I have been looking into https://github.com/m-labs/misoc as a replacer for the beaglebone.
This task seems rather complicated but I guess this knowledge could be really help full. The statemachine now runs on pru of the beaglebone and is limited at around 2 MHz.

- how do i balance the prism; i have done some preliminary experiments but still works needs to be done. You could also try to figure this out with a regular polygon motor. Add an imbalance and try to analyze this.

- the slicer or interpolater can only be run on a computer, as it overflows the ram of the beaglebone https://github.com/hstarmans/ldgraphy/blob/master/interpolator/interpolator.py . Remove this problem, optimize the code.

In the mean time, I am cleaning up the code, building a second head and still have to do more experiments.
I am also waiting for news on the hackaday prize. That's also why I have been quiet on the blog.

  Are you sure? yes | no

Ben Wishoshavich wrote 10/24/2019 at 22:57 point

I'm wondering if there isn't a BLDC motor that could be substituted for the polygon motor, hopefully something that is more available. And then I'd need an encoder. I'll take a look at this, although I suspect going greater than 20k rpm requries air bearings and a custom design.

The rectangular prism does seem to be a challenge. I'll let you worry about that. Out of curiosity, do you know how much it'd cost for a custom order?

An FPGA should be able to handle the state machine. I'm working on the FPGA that's in the Hackaday Superconference badge, and it's got an open toolchain. It might be overkill though. The ICE40 may be better(and cheaper). I might be in the minority in that I'm not sure this is a huge priority, as your electronics are pretty cheap. It's probably a pretty significant time sync to rewrite the assembly for the PRUs into a state machine. I'd probably focus on a command and control system to interact with GCODE or something else.

 I could jump into the MCAD, but I only know Solidworks. I suspect someone else might be better suited for that.
At work, we have specifications for balancing motors for EVs. The most relevant standard is ISO1940. Let me know if that's useful for you. Usually a balancing machine is used to detect vibrations while the part is rotated. They're pretty rare and fairly expensive though. They do make some simple ones for balancing quadcopter props you could look into. Usually you have to add or remove material in a specific spot to make it work.

I already have some of the parts you've used. Perhaps it won't be as hard to duplicate some version of this as I expect.(expect for that lens).

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Hexastorm wrote 10/25/2019 at 17:13 point

-  i wouldn't substitute the motors; they have been used in this application for years by a large industry. Rotating polygon mirrors are produced in the tens of thousands. Motors can handle up to 21000 RPM.  This is more than what is needed at the moment, 2400 RPM, as the beaglebone can't go faster.
- custom order is around 500-600$ and MOQ is 10. for the prisms
- Henner zeller wrote a GCODE parser for the beaglebone called beagleg; my idea is that this used and you simply flip the machine between gcode mode and laser writing mode
- never heard of this standard good tip
- all parts are easy to obtain including lenses, motor etc; the only challenge is the prism and time. You will need time :-)

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rajhlinux wrote 01/01/2021 at 08:17 point

well you can count me in, i'm interested with this project

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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"?

  Are you sure? yes | no

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, a description of the process is in this log https://hackaday.io/project/21933-open-hardware-fast-high-resolution-laser/log/167433-how-to-be-transparent

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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.

  Are you sure? yes | no

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.

  Are you sure? yes | no

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 (https://www.alibaba.com/showroom/polygon-motor-ricoh.html) .  The system is a proof of concept; for desktop PCB prototyping 2400 RPM is fine. If you plan to compete with Kleo https://www.youtube.com/watch?v=7R464iHaTQU . 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 https://precisionlaserscanning.com/2016/03/road-runner-70000-rpm-polygon-scanner-solves-the-noise-problem/

  Are you sure? yes | no

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.

  Are you sure? yes | no

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

XMOS stuff actually does have lot of support (https://www.xcore.com), examples (https://github.com/xcore/) 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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rajhlinux wrote 01/03/2021 at 13:24 point

This is a good idea, but honestly I think the best thing is to focus on getting the precision as perfect as possible. There's no consumer grade PCB maker device that can give traces/spaces resolution down to 0.01mm. It's crazy we are still using tonner transfer and UV exposure. I'm planning to build a CNC gantry made from granite, magnetic actuators and air bearings to get the most accurate, friction free, repeatable long term PCB manufacturing with >0.7 traces and spaces. But yes, would be nice down the road to have the scanner head removed for another tool... but for now precision is priority. Precision & Resolution is the reason why this project brings my interest and everyone here.

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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.

  Are you sure? yes | no

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.

  Are you sure? yes | no

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 https://github.com/hexastorm/opticaldesign . 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 for the current spot size and line length.

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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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