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CaliKirk

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Well, it would be 1055, as I got 527.6.
Still unusual. Should not be happening.
So your getting about the same thing? This is wild guys!
 

Cyparagon

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I think these patterns are due to internal reflections in the foil. The light just bounces between the surfaces just as it does in a pane of glass...
That would not explain the intensity patterns, nor why it doesn't happen with the vast majority of green pointers.

A 532 nm DPSS laser should not produce other wavelengths.
I agree. However, I've confirmed it can happen - using a commercial spectrometer.
 
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Sta

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I think these patterns are due to internal reflections in the foil. The light just bounces between the surfaces just as it does in a pane of glass, giving some lines in places they should not be.

A 532 nm DPSS laser should not produce other wavelengths. The doubling process is very selective when it comes to incoming wavelength, which is 1064 nm from the solid state.

If the emission was as broad as the pictures suggest it should actually be very easy to construct green lasers anywhere between 525 and 531 nm just by adjusting the reflective coating. Realistically something like that is not possible (try to find any such lasers for sale), and i think it must simply be an artefact of using this type of grating.
Benm, I can't agree. The furthest lines have a distinctively yellower color. And CaliKirk and I got identical results from using different gratings (flexible vs. solid.) A grating should not change the wavelength of anything -- it simply cannot have that property.
In addition, I observed the same effect with my 589, making it likely that this is due to coatings, and not the grating.
 
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diachi

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Benm, I can't agree. The furthest lines have a distinctively yellower color. And CaliKirk and I got identical results from using different gratings (flexible vs. solid.) A grating should not change the wavelength of anything -- it simply cannot have that property.
In addition, I observed the same effect with my 589, making it likely that this is due to coatings, and not the grating.

He's not saying it's changing the wavelength, just that it could be down to internal reflections in the grating or some other part of the "system".

But it's not that seeing as we've verified that the colours are different, intensities don't look like they result from internal reflections, have tried different setups, not all lasers do it and Cyp has tested it on a commercial spectrometer.

Definitely not a result of the setup - the lines are clearly there.
 

Benm

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From the photo's i cannot tell any difference in colour, but that is probably to be expected. If you see it in person i'll take your word for it. Gratings, prisms and such cannot change the wavelength, so it must come out of the laser as such.

Given that the phenomenon is real, investigating it further sounds like a good idea. One first step would be to re-confirm the findings using a different means to split the lines, like a glass prism. Since the wavelengths are quite close this will not be easy, but not impossible either.

The next question is finding what actually causes this. I think you would need to disassemble the laser and see what the output of the 1064 nm light is like. I would expect this to be a single line, but to get doubling to a range of wavelengths it has to be multiple lines.

I assume the solid state laser is Nd:YVO4 here (with a single line at 1064), but that might not be accurate. It could be something like Nd:YLF that has lasing lines at 1047 and 1053 nm. Or perhaps it's come contaminated material that has properties of both, it's really hard to say/speculate on that.

To get to the bottom of this getting a spectrum for the solid state laser is essential though. This may prove somewhat difficult as the light is invisible and probably mostly blocked by the IR filters in most cameras as well.
 

CaliKirk

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I'm still waiting for some other gratings to arrive so I can run some more tests and further try to figure out whats going on. But I did ord er (23) pen style 532s :). So we shall see what the outcome of that will be as plan to test all and report back my findings.

One thing I noticed while going through so many cheap 532s, is that the auctions I won that were extremely cheap, like $1-$5, was resulting in me being sent more units that had issues such as being overall dim, button problems, or would be super bright for a millisecond or so then dim down, and it wasn't untill I checked the stockpile of sub par unit (units under 50mw or issues) with a grating that the multilines started appearing. On all the units that were 50mw and up were single line and still I have not found a multiline on any above that power.

I also have noticed that on most of the units that I felt had issues and kept, had red marking under the lens assembly that was not consistent with others. Maybe something to do with quality control, idk.
 

CaliKirk

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Sorry for the double post, felt a new was needed.

So I got a free piece of 1000/mm grating sent to me graciously by paul1598419 and the first thing I did was get some lasers together and start testing!

First lasers I tested were as follow:

Challenger 2 with bdr209= 411.57nm
PLP520b1= 517.88nm
M140= 448.31

Grabbed a known 532 (single line) to make sure I was on the right track.
= 532.82nm yep!

I tested a 301 I have that no matter what temperature it stays on (4) lines and they are:
1= 532.04nm
2= 537.20nm
3= 541.98nm
4= 549.72nm

I went inside and grabbed the 8 line, house was set to and has been at 74°F so id image the laser was very close to the same temp if not higher as it was sitting near my Comcast box. The first order again is coming out to 527 :wtf:
1= 527.93
2= 529.99
3= 532.79
4= 535.01
5= 537.77
6= 540.70
7= 543.25
8= 545.78

While doing the above calculations and burning a couple holes in some cardboard, I had the 8 line 301 sitting in the fridge and left it for about 20 min or so, laser was 38.7°F.

For the next (3) tests, the laser was taped ON and nothing was moved, the rig I made that is holding the grating and laser stayed put and I did all my identifying marks first then calculations after. Again I just pulled it out of the fridge, and also the garage I tested in was ~60°F

After taping and leaving it ON for (1) minute, the laser was operating with (4) lines which ive seen it do many times when cold.
1= 529.25
2= 530.37
3= 534.64
4= 539.24

After the laser being on for 8 min, again nothing was moved the entire time. But as I'm laying on my stomach, im watching all of the lines changing intensity and some completely fading but almost ALL of the spots changed their position on the wall, some of the changes were very quick, mostly slow but pretty obvious. I was thinking of doing a video but do not know how to speed the video up.

Here's after laser being on for 8 minutes:
1= 528.50
2= 533.34
3= 536.12
4= 538.32
5= 541.25
6= 543.79
7= 546.50
8= 549.37

Laser being on total of 16 minutes:
1=528.12
2=532.79
3=536.12
4=538.14
5=540.70
6=543.79
7=545.96
8=548.65


After this test the laser was only 69-70°F. And if you look at the numbers from todays earlier test with the laser being at or above 74°F and comparing that with numbers as the laser is warming up, it looks like as it gets warmer, all of the lines are moving to lower WL. I wish I took the lasers temperature at all my testing intervals but there's always next time!

But when it is super cold, it looks like the first order is 529.25, then as it warms up the first order transitions slowly up to ~527. All of my previous testing done in this thread was mostly done with the laser being warm, maybe once with it being left in the cold garage while testing other lasers, but most of my past readings were with the first order starting at 527.

I will be doing more tests tomorrow, on more lasers, and will do the same thing with the 8 line laser, with it being completely cold to warm and taking both temperature and WL measurements at different intervals and maybe even leaving it on for 25 min this time. I'd like to take a video too and find a way to speed it up to watch the lines transition as it warms up. One thing that is very obvious with the 8 line is it is completely yellow tinged compared to my other 532s while looking at the focused spot. :beer:
 
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paul1598419

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As the laser warms up and the wavelength decreases the light frequency is increasing. I have found the same thing with single line 532nm lasers on my spectrometer. It isn't a huge difference, but it does change.
 

Cyparagon

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As the laser warms up and the wavelength decreases the light frequency is increasing.
I'm pretty sure atomic transitions of Nd don't change with temperature. I welcome a correction if you can find a source. A green pointer is 532.09nm at all times. Any variation you're reading from this is variation in your instrumentation.
 

paul1598419

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I was talking about these very cheap pointers that can be had on eBay for $2.00. I have watched it change over time as it heats up. Not a great deal, but it does change and if others are seeing this also, I doubt seriously that my USB2000 commercial spectrometer is the fault.
 

lazeristasUVISIR

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But when it is super cold, it looks like the first order is 529.25, then as it warms up the first order transitions slowly up to ~527.
What do you mean the first order? Has it highest intensity? wavelength? Just the first spot on the left (right)?

The "first order" is used in connection to grating diffraction orders. (look for pictures "grating orders")
 

lazeristasUVISIR

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I'm pretty sure atomic transitions of Nd don't change with temperature. I welcome a correction if you can find a source. A green pointer is 532.09nm at all times. Any variation you're reading from this is variation in your instrumentation.
There could be variations in that number due to a multimode (longitudinal) operation.
 

CaliKirk

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What do you mean the first order? Has it highest intensity? wavelength? Just the first spot on the left (right)?

The "first order" is used in connection to grating diffraction orders. (look for pictures "grating orders")
The first "spot". Apologize as gratings are new to me, I thought the zero order was the center dot, and first order was the first spot then second and so on..

The intensity changes (meaning the brightness of the spot itself), depending on lasers temperature the most intense spot changes from the first spot to the 2nd to 4th. Only my 8 line does that, the first spot on the others is definitely the brightest.

And as the laser warms up, with zero human interaction and inside a closed room with no wind, the first spot on the left can be marked while the laser is cold, and one can watch the spot changing both intensity and moving away from the initial mark when the laser was cold, thus moving closer to the center line.
 

Cyparagon

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There could be variations in that number due to a multimode (longitudinal) operation.
Source?

I have watched it change over time as it heats up. Not a great deal, but it does change and if others are seeing this also, I doubt seriously that my USB2000 commercial spectrometer is the fault.
You're seeing the wavelength change, or the power? By how much?
 

paul1598419

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Source?



You're seeing the wavelength change, or the power? By how much?
Didn't pay attention to the power, but the wavelength changed by ~.50nm over 5-8 minutes. It decreased from 532.20 to 531.69, IIRC.
 

Cyparagon

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It decreased from 532.20 to 531.69, IIRC.
Are you aware your device only has 2048 pixels to cover the spectrum? Depending on your grating, That's probably less than 3 pixels per nm. That second decimal is an artifact of the polynomial calibration regression, and should be rounded off. The average beam position would only need to move one pixel over to account for a drift of 0.5nm. You don't think it's possible ANY thermal effects internal to your device could account for a 1-pixel shift?
 
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