45 Deg Dichroic blocking blue, transmitting red & !520!

[Svenvbins]

I bought a cheap set of dichro's for my projector. One passes green and reflects blue & red and the other passes both green and red and reflects blue.

The second one is problematic, while its specs say it should pass green pretty well, it actually reflects about 35mW of my 50mW 520nm laser. The fact that it's 520 instead of 532 probably doesn't help much either.

My simple question: Can anyone recommend a cheap dichro that does pass my 520nm better than the current one? Atm, I have to run my blue and red at ~30% in order to maintain color balance

 

[Alaskan]

I bought some at what I thought was a good price but have not checked them yet. I have a 520nm laser, will see what I can do to tell you if mine are any good either:'

Dichroic Mirror Red and Blue Filter for RGB Lasers | eBay

I hope these aren't the same ones you are having a problem with, have you tried 532nm to see how it behaves with that?

 

[Svenvbins]

Huh, it's a small world! Those are the ones I bought, too Thanks for offering to check them, anyway!

Didn't try with a 532 because I don't have one. Ordered one at DX, but never arrived, so now I'm waiting for their customer service to send a new one or refund the ~$3

As for the specs provided in your link, I'm not too sure I trust the BDM one. It states >90% for 520, which really isn't the case with me. I can't verify I'm at exactly 45 degrees, and I know it's sensitive, but it's 45 degrees by eye, and I don't think that should drop efficiency down to 30%.
Well, if you've got the time, maybe you could do a quick check on how sensitive it is to the angle?

 

[Alaskan]

Oh no! Maybe they won't work for my intended 520nm project either

I will check later tonight for both 520 and 532 and see what my LPM shows. If you are not sure of the angle, you can slowly sweep through what you think is close to 45 degrees back and forth to look for a peak.

 

[Svenvbins]

Good luck, let's hope I just got a faulty one!
Did manage to find an angle where the *reflection* was ~100%, but that of course is the opposite of what we want. (FYI, angle between incoming & reflected beam was about 30deg, although that's really rough & from memory, since I didn't look very close for obvious reasons )

Can't really measure accurately without LPM, but what my eyes could see didn't really show any improvement over other angles.

Should ask around in our lab whether anyone happens to have a nice dichro with a small crack they can't use anymore ^^

 

[Alaskan]

OK, after a lot more testing I'm editing this whole post completely from what I said earlier tonight:

I put my 520nm DTR module in a heat sink and was then able to do longer testing to provide better results. At about 45 degrees my 63mw output 520nm laser diode is being attenuated down to 58-59 mw, so I'm loosing 4 to 5 mw or somewhere between 7 to 8%. I'm holding the dichro by hand and the angles are surely not very accurate in either plane, but there's a rough report for you. I'm hoping a proper setup and exact angles will reduce the loss.

At 532nm I'm getting similar results but I'm not sure if that is due to IR being attenuated by the dichro too. Also, the glass has a bit of dust on it now I took it out of the package and fumbled with it in my fingers too much too, maybe affecting the results a little. If you get another one from that seller, please PM me the results, OK? I don't always see responses in older threads.

 

[Svenvbins]

I put my 520nm DTR module in a heat sink and was then able to do longer testing to provide better results. At about 45 degrees my 63mw output 520nm laser diode is being attenuated down to 58-59 mw, so I'm loosing 4 to 5 mw or somewhere between 7 to 8%.

(...)

If you get another one from that seller, please PM me the results, OK? I don't always see responses in older threads.

Huh, interesting. Should still be <5% according to their graph, but at least it's much closer than what I measured... I'll see if I can take the LPM home for the weekend and re-test mine. I know what I saw (>50% loss), but I hope with some specific data I can convince the seller to send me a new one, as it seems I might just have a faulty thing.

If that happens, I'll send you a pm!
(Nearly missed your edit too, was actually writing a message to the seller and wanted to link to this thread when I saw you changed the contents )

 

[Alaskan]

I'm new to dicro's, initially, for some reason thought I could test the green lasers going straight through at a 90 degree angle, when doing so I thought I saw 532nm go through with little attenuation and the 520nm not... I still don't know where I went wrong with the initial measurements because when I tried again later, I found that I had to have the glass at 45 degrees for both 532 and 520 nm or they were both markedly attenuated. Once at about 45 degrees, then the dicro passed both at that 7-8 percent loss. If I mount the glass on something and can get everything lined up better I will report the results. Also, I have several more of these to test with.