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Single line argon = 488 collimated + royal blue flashlight?

bd1323

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May 1, 2021
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I've been playing with a single line argon out of a confocal, and ran into something I couldn't turn up any answers for in my searches so thought I would brave the waters and reach out here in hope of learning something new. It starts up fine and while it seems to produce 5-10mw of 488 with a somewhat ok beam, it also is projecting a poorly collimated (41mm at 1m) but pretty bright royal blue along with it. See below:

close up of beam on cardboard across the room:
IMG_20210623_193737 (2).jpg
Now with main beam blocked:
The color here in the first picture isn't true to the eye, the blue halo is actually the same color as the brighter blue circle in the center, and representative of how it really looks, the tiny dot is 488 cyan reflecting from the wedge, the main beam is blocked. This is reflecting at an angle about 6 or 7cm from the end of the head, the blue 'halo' is not visible in the next picture at 1m, only the central brighter portion.
IMG_20210626_192530 (2).jpg
At 1m, the central bright royal blue light is about 41mm across, the primary 488 beam was still less than 1mm best as I could tell with calipers, if you used a bright object to block the beam at the source (and reflected some of the light back) you could clearly see the color difference. All the cyan below is reflections from the tiny round screwdriver blade in the beam path held against the head, it fills the dark blue circle that makes up the background. Maybe someone more adept than I could gain some insight from the reflections being limited to the same size circle or any other clues?
IMG_20210626_194420 (2).jpg
I've read through Sam's and searched here and could only come up with potentially trying to clean the surface of the optics. The only thing I could get to without disassembling things I didn't care too was whatever is in front of the optical pickup, the rest appeared well sealed still, and using a single gentle stroke per swab with 99% alcohol I didn't see anything removed or notice any change. (The inside of the laser head was/is greasy, I don't want to disturb anything too much yet by cleaning the rest of it yet).

So a question from a new guy to those with more experience, is this representative of anything abnormal, or any clues what to check for? It would make sense if some light was leaking out and bouncing around the mirrors made it roughly collimated, but this is quite a lot of light here. I have gently pressed around on the mirror mounts per instructions on Sam's but noticed no changes in output.

Appreciate in advance any advice or input!

Take care,

-Brandon
 



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My first thought would be that it is slightly misaligned or something non-normal with the optics.
It looks like the 488 output is normal though, is the 488 centered to the other light circles, are the other lights smooth/even?
I can't say I have much of an idea of what it could be.

When you say that you pressed on the mirror mounts but did not see any change, you mean you did not see any change in shape, you should see some change in brightness.
I would imagine the anomaly it is part of the laser output (not from the lighter bore discharge), so it should be coherent and at 488nm.
I am curious as to what our more experienced members have to say.
 
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Anthony P

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You got me curious (thanks!) so I tried this with 2214 SL 488. I also see the halo even with the actual beam in shadow. It is not noticeable with room lights, only in darkened room.
 

bd1323

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May 1, 2021
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Thanks for the feedback! And I am glad to hear that it is visible on other lasers as well. I tried to come up with a better way to capture this particular output, the 'halo' portion visible in the first image kind of goes away but the central bright dark blue spot is pretty bright.


IMG_20210626_193457 (2)_LI.jpg


It is just barely visible at 25 feet in daytime if you block the main beam and hold up a white piece of paper and move it around, I couldn't capture it, but it is about 24" in diameter. I kept thinking the divergence was off on the main beam but (please check my math here) it seems spot on from what I understand should be expected from a very rough test: 11mm diameter 90ish percent intensity captured at 25' is about 1mrda?
IMG_20210627_104433.jpg
I plan on playing around with this a bit more today just for fun, I want to try and find a way to get a slit and diffraction gating involved and try get a guess as to what color(s) that light that actually is out of curiosity.

Toa answer questions above, The normal output is centered in the beam, when pressing on the mirror mounts I noticed no change in apparent brightness or position or halo effect. Since I did not see a change in brightness I guess that means I was being to gentle? The front plate of the head was slightly loose on arrival and the hour meter was out of place, so it may have been jarred at some point.

The 488 is centered to the other color(s), and both are smooth and symmetric TEMoo looking but not necessarily even as there is a distinct poorly collimated beam vs. light halo cone in the dark blue. The 488 seems to exhibit what seems like a lot stronger intensity higher order Fraunhofer looking interference than I remember from my previously ML argon, and some interference patterning is visible in the 'beam' portion of the dark blue.

It is pretty interesting and not a bad little feature as long as it isn't some indication of a problem. I'm also curious about the output, at first it seemed to maybe make sense if trying to match the power of the other lasers, but the red HeNe is running at 15mw and the green is 1-2 so that went out the window, using such a low powered laser (5mw, up to maybe 10mw after warm up and turn all the way up) in what was probably an expensive system originally seemed surprising - anyone know if these confocal systems are intentionally limited in some way or is the tube probably just meeting min spec as designed?

I've tried high and mighty to search and decipher the model number from using Wayback machine and other sources and old manuals to understand what the rated output might be but have come up dry. It is a tiny little tube, about 4 inches shorter than my other ML, and seems to want about 105v DC at the head before the starter when running at idle, 451 hrs on the meter. If anyone has any idea what the specs might be I would be grateful!


IMG_20210617_163844 (2).jpgIMG_20210617_184602 (2).jpg
Thanks again for looking and the feedback, and glad I got someone else curious, I owe about a million of those back after reading though this site and Sam's!

-Brandon
 
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