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PSB cube questions

FutureOne

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Hello guys.

Have a couple of PBS cube questions. I have a couple of 445nm PBS cubes, and would like to use one for a couple of 520nm diodes.

Will that work? Or is it better to buy 520nm - 532nm PBS cubes?

And in general, once you have your diodes dialed in properly, and you're not looking at the dot of the combined beams (let's assume it's in another room), is it safe to look at the glare coming off the PBS cube without goggles?

I guess that question goes for 445nm stuff as well.
 



Alaskan

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Some PBS cubes are broadband and if purchased through ebay, they might be listed for a specific wavelength when in fact might be broadband VIS. Check with the seller or better, the manufacturer and see what they say. If you can find a graph showing the wavelength the cube was designed for as well as its AR coating, if it has one, that is what I would try to find.

Regarding the glare, I don't know if what you are calling glare is a small amount of light, or a beam being reflected off of the surface which can be close to 8% if there is no AR coating. Since you are calling it glare, maybe it isn't much light, maybe it is... I can't judge.
 

FutureOne

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Some PBS cubes are broadband and if purchased through ebay, they might be listed for a specific wavelength when in fact might be broadband VIS. Check with the seller or better, the manufacturer and see what they say. If you can find a graph showing the wavelength the cube was designed for as well as its AR coating, if it has one, that is what I would try to find.

Regarding the glare, I don't know if what you are calling glare is a small amount of light, or a beam being reflected off of the surface which can be close to 8% if there is no AR coating. Since you are calling it glare, maybe it isn't much light, maybe it is... I can't judge.
What I mean by "glare" is just the glow caused by, what I'm assuming is a small amount of diffraction caused by the cube itself on the laser beams:



As you can see from that stock pic, the 2 beams are passing thru, but the cube itself is glowing.

Is that "glow" safe to look at without goggles?

And for 520nm diodes, I take it that a specific 520nm PBS does not need to be IR coated?
 

CurtisOliver

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Be careful looking at the light, it could be do to overexposure, but the cube looks very bright. As for the IR coating for the green PBS, it isn't necessary for 520nm as their isn't any IR output. It isn't important really for 532nm either.
 

CaliKirk

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You could always paint the surfaces in the field of view with flat black paint to absorb the stray light. I wondered why alot of the used cubes I was looking at on the net had black paint then eventually figured out why.

Edit: I don't know if a special paint would need to be used but I'd imagine so..

Does your cube get hot? It does seem to be glaring pretty bright
 
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RedCowboy

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A piece of ar coated glass at a 45 angle should work, but I suppose it will need to be polarizing?

I want to combine 2 fast axis corrected beams, holding a fast axis corrected NUBM44 laser in each hand I can turn them on and off with my chin, but converging both spots at distance is rewarding, I know there are some good cubes as far as low loss, but I would like to know exactly which one, I listed one that looks good, but I have heard 2% loss is possible, any ideas?
 

diachi

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A piece of ar coated glass at a 45 angle should work, but I suppose it will need to be polarizing?

I want to combine 2 fast axis corrected beams, holding a fast axis corrected NUBM44 laser in each hand I can turn them on and off with my chin, but converging both spots at distance is rewarding, I know there are some good cubes as far as low loss, but I would like to know exactly which one, I listed one that looks good, but I have heard 2% loss is possible, any ideas?

Yes, will need to be polarizing. You can get flat PBS plates instead of cubes too. Have posted about them before. Coatings will affect efficiency, but will still work even with the wrong coatings - you'll just lose more depending on what coatings/wavelength you are using.

2% loss seems reasonable to me - that's not even going to be noticeable with a NUBM44. ~100mW loss or so. Not like you can't afford to lose a few hundred mW when you're getting a combined ~12W. :p

To answer OP - Yes, you can use a 445 cube with 520, your losses may be higher though vs a cube coated for 520. Just depends on how "wide" the coatings are on that cube.
 

Alaskan

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Only reason I prefer cubes over flat plate beam splitters is the way they can be mounted, I'm sure there are applications where a flat plate has its advantages too, but are the plates typically lower loss than a cube due to less glass?

Here's a seller of PBS cubes which are better priced than some, but small, I believe the power rating is likely too low for a pair of NUBM44 diodes, but for those who don't need high power they look great to me, I'd like to combine the output of single mode laser diodes with them:

10x10x10mm Polarization beamsplitters - Opt Lasers
 

diachi

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Only reason I prefer cubes over flat plate beam splitters is the way they can be mounted, I'm sure there are applications where a flat plate has its advantages too, but are the plates typically lower loss than a cube due to less glass?

Here's a seller of PBS cubes which are better priced than some, but small, I believe the power rating is likely too low for a pair of NUBM44 diodes, but for those who don't need high power they look great to me, I'd like to combine the output of single mode laser diodes with them:

10x10x10mm Polarization beamsplitters - Opt Lasers

Other reason is that you get no refraction due to the face of the cube being perpendicular to the beams entering and exiting. There's slight refraction with a plate because it's at a 45* angle relative to the beams.

See table 1 here: What are Beamsplitters?

They both have tradeoffs...

Those are great prices for cubes and would certainly handle any of our single mode lasers just fine. :D

One solution to increasing your power through the cube is to expand the beam before the cube and then reduce it again afterwards. You could even place the cube between the two lenses of your typical beam expander... So it'd be like a beam expander with two input lenses and one output lens.
 

Alaskan

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Power density reduced! Good idea, I want to build a RGB laser pointer by PBS combining two single mode diodes of each color for a total of six single mode diodes, but I don't want to collimate them before the cube, only some distance after the cube, letting the beams expand to about 5 inches diameter before collimation. Perhaps I could just use some 6mm diameter lenses like the G2 for each diode and only partially collimate the beams before they enter the cube, that way I could control the size of the beam entering it and then fully collimate using a large 5 inch dimeter PCX lens at the end of the pointer for a ultra low divergence white beam. Any ideas for this? One of my concerns is whether I can get all three colors to focus to infinity that way if using a simple PCX lens instead of an achromatic lens.
 

FutureOne

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Wow this thread got crazy.

Ok so questions answered so far:

1. 445nm cubes can be used for 520nm diodes, but with higher losses = fixed!! Bought 520nm PBS cube from Stanwax coated for green.
2. The "glow" from a PBS cube is what I am calling the blue light that the PBS cube is radiating out, so to speak.
See this video for example (One of Rick Trent's awesome dual 445nm on PBS cube: https://www.youtube.com/watch?v=-Ft6XZ6zbg8 - look at the 0:23sec mark. When he turns it on, there's the actual beam, but before that, where the cube is actually located, there's a bluish "glow" that permeates the enclosure.

I happen to have one of Rick Trent's combined units, looks almost identical to that one on the video, but I have never looked at the PBS cube without goggles while it's powered up. This is hard to explain in words, but the question is so simple in my mind.

When I have the unit powered on, if I am pointing the beam, let's say at the sky, there is still a very bright glow from the cube itself (due to the cube itself diffracting that 2% loss of the beam power???), and this glow is what I am wondering whether it's safe to look at without goggles. Right now I'm guessing that's a no (because it's helluva bright).

The reason I ask is because I want to make my how host, combining two 520nm diodes on my own, similar to Rick's setup there, and I'm guessing that the "glow" from a PBS cube with two 1W+ 520nm beams is probably going to be unsafe to look at without goggles either?

Hopefully I haven't confused anyone even further.
 

Alaskan

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From your description, speaking for myself, I would not have any issue glancing but not staring at the glow, a high powered reflected beam yes, don't even glance at that. There are members who build plastic see through windows on their laser pointers which use these cubes just so they can see the glow.

I doubt anyone here is going to say it is definitely OK to look at the glow because safety isn't an area to guess at when we don't really know for ourselves how bright that glow is. I guess my answer is maybe, if it isn't too bright which is subjective and no answer at all. Best I can answer without seeing it myself. Here's a clue though, if after looking at the glow you have a spot in your vision which takes a few seconds to go away, that was too bright to stare at. If using blue laser diodes this can be a different story even without producing a spot, they can bleach the cones of your eyes when too bright.

Since you have already looked at it, can you tell us if doing so produces a spot for a few seconds?
 
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FutureOne

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From your description, speaking for myself, I would not have any issue glancing but not staring at the glow, a high powered reflected beam yes, don't even glance at that. There are members who build plastic see through windows on their laser pointers which use these cubes just so they can see the glow.

I doubt anyone here is going to say it is definitely OK to look at the glow because safety isn't an area to guess at when we don't really know for ourselves how bright that glow is. I guess my answer is maybe, if it isn't too bright which is subjective and no answer at all. Best I can answer without seeing it myself. Here's a clue though, if after looking at the glow you have a spot in your vision which takes a few seconds to go away, that was too bright to stare at. If using blue laser diodes this can be a different story even without producing a spot, they can bleach the cones of your eyes when too bright.

Since you have already looked at it, can you tell us if doing so produces a spot for a few seconds?
No I have never directly looked at the glow coming from the cube without goggles. I can just tell it's bright from the corner of my eyes how it makes the room light up.

And yes, the reason I was asking is that it would be cool to make a host that had a see-thru window so it would look "cool". But safety is far more important than "cool" so I'll just put it in a host that encases the whole thing to not be visible.
 

diachi

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No I have never directly looked at the glow coming from the cube without goggles. I can just tell it's bright from the corner of my eyes how it makes the room light up.

And yes, the reason I was asking is that it would be cool to make a host that had a see-thru window so it would look "cool". But safety is far more important than "cool" so I'll just put it in a host that encases the whole thing to not be visible.

It'd be relatively easy to work out how safe looking at the cube is or isn't. Sit an LPM 1" from the cube, calculate the area of the sensor, check what the power reading is (if it even reads anything). Divide the reading get by the ratio of your power sensor surface area to your pupils "surface area" when fully dilated (Roughly 200mm^2 I believe?). That's then roughly how much light can enter your eye (while fully dilated) 1" from the cube.
 

CurtisOliver

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Nice tip Diachi. It could be camera overexposure that is making the cube look dangerously bright. But with beams like that, goggles should be worn anyway.
 




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