What's this orange coming from my 520?

[Eracoy]

I have a couple 520nm diodes, a PLP-520-B1 and a NDG7475, and I've noticed that their dots look yellow when viewed through red-tinted low-wavelength-blocking goggles. Now, of course we all know that red and green make yellow, so what is the issue? My eyes are clearly seeing the combination of red tint and green light to perceive yellow!

The problem comes when I shine the laser through the goggles themselves. Green goes in one side, and is almost entirely blocked, but a golden yellow comes out the other side. To keep from burning my goggles, I used a beam expander to spread the width at aperture and a cheap pair of Ebay-Specials:

It is not scattered, either! I can easily focus the light down to a point, seen here close up

It is on the order of a milliwatt or two, judging by eye. I even ran it through a diffraction grating to see if it was some odd combination, but it came out as one wavelength. My question is this: What's coming out of my laser?

 

[Gabe]

That is pretty strange. Have you ran the regular collaminated beam straight from the diode into that diffraction grating, put onto a wall very far away so you can go up to it and see if you can discern any second lines? This is also a total crapshoot from my end but could this have anything to do with fluorescence? Your goggles might be slightly fluorescent under green light, or by some other chemical property the light passing through gets bumped up to a longer wavelength? I don't even know if that's possible. Have you tried it with a 532 to see if it's the laser or the goggles?

 

[Eracoy]

From a 532, I do see a very faint dot coming from it, but not nearly as bright as that from a 520. I would suspect the goggles, as they are the common factor here, but I don't know of a phenomenon that would both change the color and preserve the collimated beam. Fluorescence would scatter the light it produces, correct?

 

[Sta]

I've noticed this as well. They definitely fluoresce but I am not sure what the actual process is. It may be the some of the fluorescent light retains its direction.

 

[Gabe]

From a 532, I do see a very faint dot coming from it, but not nearly as bright as that from a 520. I would suspect the goggles, as they are the common factor here, but I don't know of a phenomenon that would both change the color and preserve the collimated beam. Fluorescence would scatter the light it produces, correct?

Yeah fluorescence wouldn't preserve the collamination. But it must be something to do with the dye in the plastic of the goggles.

 

[Sta]

Yeah fluorescence wouldn't preserve the collamination. But it must be something to do with the dye in the plastic of the goggles.

Actually you are right. I thought it was possible that the goggles themselves might be lasing.

 

[Encap]

Actually you are right. I thought it was possible that the goggles themselves might be lasing.

That would give an entirely new meaning to the term 'laser goggles" :crackup:

 

[RedCowboy]

This blue NUBM08 does the same.

Could it be these absorb type glasses are converting a fraction of the lights wavelength or fluorescing?

 

[H2Oxide]

This has been observed before. See this thread.

I doubt it has anything to do with the goggles themselves. Try shining it through a diffraction grating.

Also, what's up with the tags?

 

[Gabe]

This has been observed before. See this thread.

I doubt it has anything to do with the goggles themselves. Try shining it through a diffraction grating.

Cheers man, that might solve it. For anyone else who's too lazy to read the whole thread, it basically comes down the owner of the diode shipping it off to a member with a spectrometer, and once spectro'd we find out the laser really is giving out secondary lines in the 590+/- range. I would've never have thought to use the search bar on this, but I guess it goes to show how much information is archived in these forums.

Also, what's up with the tags?

:crackup: lol I didn't notice that, must be someone who knew the answer but wasn't nice enough to reply about it.

 

[ZRaffleticket]

Gotta love that search feature. I have no idea how any of us find these things by accident, but surely it does happen. Look into multiline 589nm lasers for some other fun phenomenon.

You say this happens with the 1W diodes as well as their lower powered counterparts? I think that's pretty interesting in its own right. Can anyone test this on our newer 465nm diodes?

Edit: Look into under-driving those NUBM07E 465nm diodes that came out a while back. I'll try to find some pictures as soon as I can get some spare time. I might also have some in some old, old PM's. Those get a spectral pattern somewhere between a multiline argon and an LED.

 

[Eracoy]

I happen to have a NUBM07E right here. With the same setup of shining it through an expander then filter and focusing it on a white wall a meter away, I get this shaky little dot:

It looks like there is a little bit of a red-ish halo around the dot, and it shows up a bit in the picture. However, it is mostly a <5mW dot of blue.

 

[Benm]

It's probably fluorescense from the goggles indeed.

As Redcowboy's photo shows it clearly goes off in other directions than straight with the laser beam, and seems to bounce around due to internal reflections lighting the entire goggle up a bit.

It is actually possible that a small amount of non-coherent red/orage/yellow light IS produced in the laser diode due to imperfections in the semiconductor. A similar thing can be seen in some blue LED's that actually emit a tiny amount of usually yellow light when at a voltage to low to produce any blue (that just overwhelmes it, the yellow is probably still there).

 

[Cyparagon]

I'd guess this is from the diode itself. This would almost certainly be spontaneous emission, and not stimulated. Diodes can still produce a "dot" even when not lasing, as the emitting area is small enough to still be collimated. The goggles will fluoresce as well, but that contribution would not be collimated.

 

[Atomicrox]

Do you see a speckle pattern in it? If you don't it's not laser light.