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Laser Beam Angle

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RolandSpec

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Apr 14, 2021
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I've been lurking here while working on my first project involving lasers. Basically it involves using multiple lasers to predictably land in specific places.

So, I designed a "jig" of sorts to hold my diodes at specific angles in various directions, etc. But I spent all day scratching my head as to why the lasers weren't landing where the math said they should be.

I now realize that the *very* cheap (5mw 650nm) laser diodes I got likely aren't shining the beam at a perfect 0 degrees from reference of the laser body.

Laser Angle.png

Account is too new to post a link, but here's a picture of the diodes I got:
61afIQfExCL._SL1500_.jpg Very cheap Amazon specials.

Is this a quality inherent to laser diodes? Or can I spend more money and get lasers that will shine the beam at 0 degrees? Ideally I need them to have a "body" like the ones in the link above, just for packaging purposes in my jig. Basically I can't get any sort of PCB or anything in the space. But I'm open to learning other mounting methods for lasers when accuracy is important!

I'd love recommendations on similarly packaged lasers that would be accurate as well, if they exist!

Thanks for any advice on this :D
 





RolandSpec said:
I've been lurking here while working on my first project involving lasers. Basically it involves using multiple lasers to predictably land in specific places.

So, I designed a "jig" of sorts to hold my diodes at specific angles in various directions, etc. But I spent all day scratching my head as to why the lasers weren't landing where the math said they should be.

I now realize that the *very* cheap (5mw 650nm) laser diodes I got likely aren't shining the beam at a perfect 0 degrees from reference of the laser body.

View attachment 72381

Account is too new to post a link, but here's a picture of the diodes I got:
View attachment 72382 Very cheap Amazon specials.

Is this a quality inherent to laser diodes? Or can I spend more money and get lasers that will shine the beam at 0 degrees? Ideally I need them to have a "body" like the ones in the link above, just for packaging purposes in my jig. Basically I can't get any sort of PCB or anything in the space. But I'm open to learning other mounting methods for lasers when accuracy is important!

I'd love recommendations on similarly packaged lasers that would be accurate as well, if they exist!

Thanks for any advice on this :D
Click to expand...
Personally, I wouldn't expect that much from those cheap LD's, I still have +80 of those, (bought 100pcs for 25EUR IIRC?) all of them differs and collimation lens is plastic. Quuality is... -well.. what to expect for that price..

-If you want 0 degree angle, I suggest to spend few more dollars for it :D :D
 
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Thanks for your reply! That's what I figured.

Do you have any recommendations on specific diodes I should look at? When searching my usual hobby electronics websites, I only found through-hole or surface mount type diodes. But it would be very beneficial if I could find good ones with some sort of "body" that I could use for mounting.
 
High end lasers have a term in their specs that refers to how true the beam is compared to its housing... forget what they call it.
 
Anthony P said:
High end lasers have a term in their specs that refers to how true the beam is compared to its housing... forget what they call it.
Click to expand...
Ah! That would be most useful LOL I tried Googling this but didn't turn up with anything...
 
Beam centering, deflection, deviation, misalignment, etc.
It's not necessarily fault in the diode. This can also be caused by decentered or tilted optics. If the manufacturing process is not precise, there are many points where misalignment can be introduced.
There are solutions for this. You can correct it mechanically by implementing a 2-axis aiming mechanism or you can deal with the problem optically using wedge prisms to steer the beam. There are practical drawbacks to each method so you will have to decide what is most important for your project.

If good centering is important, you can get modules that are supposed to have good alignment right out of the box:
 
It's called pointing accuracy/angle. Cheap components do not go through the same measure of quality control.
 
RolandSpec said:
I've been lurking here while working on my first project involving lasers. Basically it involves using multiple lasers to predictably land in specific places

I now realize that the *very* cheap (5mw 650nm) laser diodes I got likely aren't shining the beam at a perfect 0 degrees from reference of the laser body.

Thanks for any advice on this :D
Click to expand...

You can't expect much in precision alignment from laser when 10 of them cost about as much as a good cup of coffee--could be much better but...

Take one apart and see if you can push things around and make slight adjustments of the beam alignment on a one by one basis if everything is not potted in the module.
 
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It's not about being cheap. There's just no need for the beam to be aligned precisely with the housing for most applications. You'll find the same 'problem' in a laserglow pointer.
 
Thank you guys for all the replies and recommendations! It was interesting to research and find some options for lasers with pointing accuracy and centering spec'd.

@RA_pierce , I'm interested in perhaps trying to correct this with optics. Is there any type of lens that would correct a beam angle to 0 degrees in reference from the lens?

Something like this?

1618983534999.png

I guess the example desired situation:
1618983875614.png
 
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A wedge prism with the right wedge angle can do this but finding one that is just right for your laser will not be easy and likely not cheap. I've done this with a yellow laser.
To do this, you will need to precisely measure the angle of the beam relative to the module and find a wedge prism that can compensate. The specification you want to look at is ray deviation or power (in diopters). See here: https://www.edmundoptics.com/f/wedge-prisms/12456/
More complex arrangements of optics can achieve better results but is probably not worthwhile for low cost laser modules (unless your project demands it). Look into "beam steering" if you want to know more.

Mechanically aiming the laser is probably the better option and using optics is something you can do if the laser is constrained and cannot be tilted to compensate for misalignment.
 
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