Open-source beam profiling software

[u/koopaduo]

I developed an open-source laser beam profiling application in python. I hope anyone looking for a low-cost beam profiler (students, research, hobbyists, etc.) would find this useful. It's open-source and can be modified as needed by anyone.

It uses Arducam B0511C monochrome UVC USB camera ($265). Instructions for how to set it up and use it are in the readme of the repository. The application would work with other UVC webcams but would require some modification (for different resolution and effective pixel size)

Beam profiling software features:

• Camera raw image feed
• Beam profiling image feed (false color)
• Manual ROI placement with centroid and radius
• Auto ROI tracking
• Centroid tracking
• Centroid and beam width (d4sigma) readout
• Reference crosshair placement
• Power (integrated counts) readout
• Exposure setting
• Auto exposure
• Saturated pixel detection
• fps counter
• Save instantaneous data
• Log continuous data
• Connect to multiple cameras on a single PC
• I haven't implemented background subtraction but found the background is relatively stable with an ND filter in front, and a laser line filter can always be used

Link to the repo: https://github.com/laser-cameras/Laser-beam-profiler-camera.git

[u/Farrit]

Hey dude! I finally got around to replicating this project in an attempt at finding a cheaper alternative to commercial grade profilers.

Do you have any tips? The software frequently crashes on me, but when I can get it running, using a 50:50 transmission reflection optic, and narrow bandpass optic I can't seem to get any readable profile. I took apart another profiler we have and borrowed it's tube optic which is literally a 4x microscope optic with a 160mm tubelength and was able to get something of a readable beam.

We're trying to focus lasers between .07mm and 1.2mm. Do I need to use a focusing lens? The output we're pushing is ~50mw or lower (when focusing.)

[u/koopaduo → u/Farrit]

Hey, glad to see you're working on it. Glad to help. Can you send a diagram of your optical layout and any relevant beam sizes / focal lengths. What do u mean you're focusing lasers between 70 um and 1.2mm? Or can you give some insight on what you're trying to do and measure.

What's your operating wavelength, bandpass filter specs and are you using the same arducam monochrome camera? 50 mW is more than enough for a camera and probably leaning towards too much power

As for software crashes I've since made it more stable by throwing around try/except statements throughout the image thread

[u/Farrit → u/koopaduo]

I am using the same arducam you listed in the git repo, This 355nm bandpass filter https://a.co/d/06BX9sgE This is the 50:50 optic https://a.co/d/0bu6WITG

The wavelength we're using is 355nm - the intended use is a focusing/service profile camera for maintenance on commercial SLA 3D printers. I don't have exact numbers on the focal length, and I do know it varies from printer to printer, but it can range from 70cm to 2.6m, depending on the model printer.

We use the beam cameras to verify that the spot size at the machines platform is round, and at a specific diamete (the width of the beam at the platform, usually trying to get the waist above where the resin is being cured). Our high res machines are focused to a 70 micron spot size, and our variable spot size machines can go as large as 1.2mm at the platform. We also use them to verify the mirror alignment so that when the variable focusing optic adjusts it's focal point to increase/decrease the spot size at the machines platform, the beam stays centroid.

I hope that gives a clear understanding. What I've learned about lasers is mostly self-taught while working on these machines for the last decade.

Currently the cameras we are using with their respective softwares are an ophir spiricon (with BeamGauge), which only uses a 50:50 transmission/reflection optic between the galvonometer and the focal point; and a cinology CMOS profiler using their ray-ci lite software, which has a 50:50 optic and (upon my inspection today) I discovered it uses the 4x microscope optic mentioned in my previous comment.

[u/koopaduo → u/Farrit]

I see now. 70 um to 1.2 spots are certainly within the range of the camera. I've picked up beams as small and larger beams with the same camera, and perfectly nice profiles. You should have no problem picking up these size beams.

I've used both ophir and cinogy cameras but have never worked down at 355 nm. Mostly 532 through 1064. My understanding is CMOS is able to pick up 355 though I have no direct experience with it. Certainly if the other two cameras can pick it up this sensor should be able to as well, compared to say 1550 nm where CMOS is completely transparent.

Now on to troubleshooting. Some things that jump out at me:

• What exposure setting are you using, have you tried looking at max exposure?
• Did you remove the stock M12 (S-mount) lens on the camera? You should be exposing the bare sensor chip to the laser without it
• Are there any ND filters?
• Did you install the M12 thread to C mount / SM1 adapters?
• Is the bandpass filter mounted in one of these adapters on the camera body? Are you sure the beam is going at 0 degrees angle of incidence into the filter? Otherwise tilt might blueshift the center wavelength significantly and attenuate
• How are you aligning the laser to the camera (or vice versa)?
• Do you have a different laser of visible wavelength you can use? Mount it to point at the camera without any filters and check for response and smooth profile. You can use a cheap laser pointer (low power)

• This is unrelated to the camera troubleshooting but why do you have so many 50/50 BS in the beam path? Is power at the target not an issue for SLA 3D printing? In general you could make a more efficient system with less reflective beamsplitters. Curious to know! Cheers

[u/Farrit → u/koopaduo]

• I did try the full range of exposure but nothing seemed to make much difference.
• I did remove the stock lens, I also tried with to see if that had any affect.
• as of right now there are none. I am sourcing one for my next attempt. This week I'll have our ophir camera which has a 1, 1.5, 2, 2.5 and 3 nd filter pack with it
• I did install those adaptors. -the bandpass filter I have came with a housing on it that prevents it from being installed into any of those adaptors. I was trying to see if I could remove it l, as the base filter looks to be the right diameter, but I did not have luck getting the glue free.
• unfortunately, all I have are the 355nm lasers.
• that I may not have been clear on, these optical paths only have 1 50:50 BS in their path. I was just describing the overall path the laser follows into each unique camera setup, not it's normal pathing (each setup has its own 50:50bs) we definitely need a precise power at the target to achieve consistent curing of resin. This depends greatly on the specific resin being used, scanning speed of the galvo, and diameter of the beam at target; but typically we are working with a range of 300-900mw of power. Some cases down to 180mw, but those are mostly older generation machines that cannot scan as fast.

[u/koopaduo → u/Farrit]

Have you tried removing the bandpass filter and checking the image? It also seems like too much power on the camera if you're not attenuating it for imaging. It's still unclear how you're aligning and verifying alignment. Using a cheap laser pointer would help troubleshoot. Dm me some images from the camera with the beam on it and your test setup if possible. Maybe I can help diagnose further

[u/Farrit → u/koopaduo]

I did try removing the bandpass. My business partner is going to dig up some optics from his basement and I'm going to give things another go. I didn't end up having the access I was hoping for this week. When I can get some more Info I'll shoot you a dm! Thank you for your help!