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NUBM44.......Share your Ideas, concepts, videos, builds and more.

GSS

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Hi GSS,
The g7 is roughly the same as the g2 on my 44 builds as far as the line. I prefer the 3element. I haven't noticed the 3ele getting hot in my builds as I have seen others post. May be a matter of how clean it is. I do occasionally put a g2 in mine for up close (6") burning as it is noticeably stronger. Debris has burned into a 3ele lens I had so keep them clean
Hmm, so this a hard one to tame. I was going to get a G7 just for this build. My 3 element sure does get hot but its with that standard small focus ring, also its in a small barrel. Good to know to keep it clean and that much heat sure can't be to good for it. Can't say the G2 gets hot as it has a big custom focus knob.
I should try a variety of 3 elements. Whats the best dot youv'e gotten with a 3 element at 6 ft.?
 



GSS

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Thx VV, really nice of you for posting pics:)
Other than the heat, its the same around 3/8in, like I had posted. I'll just stick with
the 2 lenses, for now anyways:thinking:
 

Alaskan

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I took off the lens from my Ehgemus NUBM44 host and used a large 3 inch diameter film projector lens assembly and wow, I can focus the output to a small dot 20 feet away and burn like the dickens, no triangle spot, at least, not that I can see in that shape. I just found this thread today, don't look around the forum enough or I would have seen it earlier. I posted a rather long worded post in the Ehgemus host thread about this diode which I think better belongs here, so I'm going to cut and paste. If anyone has divergence measurements for the NUBM44 using a three element lens, I'd like to compare numbers with you to see how accurate I was in my measurements or number crunching, see the below:

The idea of getting into trouble using it outside balances the desire to do so quite well here. I can use it inside, the beam is fairly good for a daytime photo :)

Oops... smelling smoke now.


The photo on the right is more true to color on my display.

You can see the fast and slow axis orientation of the beam to the camera in these two photo's;
thin and wide sides of the beam, the thin side is the fast axis which expands more rapidly over distance.​


Divergence and lenses:

I am adding this information for those who are new to laser diodes, the lenses we use and how they produce differing amounts of divergence.

I tried to measure the divergence in the fast axis/thin side & slow axis/wide side of the beam and came up with about 3.25 and 1.25 mRad (my numbers might be off some) with what I believe is a 6mm diameter three element lens. For some reason, can't remember why now, I thought this host had a G2 lens in it when I bought it, but looking closer it appears to be a three element lens. Has anyone else taken measurements with one of those lenses to compare numbers with me?

To compare common lens choices for a host using the NUBM44 laser diode; most use a lens like the well known single element G2, another choice is a 6mm three element lens, both lenses are typically close to 6mm in diameter but the G2 has much less loss while the three element lens produces a lower divergence beam, but with higher loss due to the extra glass as well as an amount of beam clipping of the light coming from the diode. I like the three element lens better for long distance spotting with a pointer due to the approx. 8mm FL it has which allows the beam diameter to have greater expansion before collimation. The classic G2 single element lens has a FL of about 4mm which produces a thinner beam but at about twice the amount of divergence. The amount of beam spreading after collimation is bad enough with this multi-element lens, I can't imagine using a G2 lens with this diode which has twice the amount of spreading per meter the beam travels. To understand the theory regarding why a thicker or wider laser beam has less divergence or spreading study beam expanders, there is a link in my signature you can follow.

Either lens you use, a low loss G2 or lower divergence three element lens, the divergence of a NUBM44 diode is relatively high:

In my opinion any pointer which uses this diode and a 6mm wide lens needs a beam expander to reduce the divergence down to that of a run of the mill 532nm DPSS laser which are typically 1.2 to 1.5 mRad, giver or take. Why? If you don't the beam becomes more of a rake of light instead of staying a beam, at least, at medium to long distance it does. Most laser pointer hobbyists don't worry about it, but if you want to put a spot on the underside of a high cloud deck, you will need beam expansion so the output doesn't turn into a wide fan of light several hundred to thousands of feet out.

Beam expanders for a single element G2 or three element type of lens:

To reduce the divergence enough for the NUBM44 to put a nice bright spot on a 5,000 foot high cloud: When using a three element lens it needs a 2-3X beam expander, when using a G2 single element lens a 4-5X expander. For myself, I use no less than a 10X expander, but when using the NUBM44 laser diode you will need to be sure the beam expanders input aperture is wide enough and the output collimation lens has enough diameter to let all of the light out. Many beam expanders have a mere 2-5mm wide input, although the beam might not be much more than 4 to 5mm wide at the input you shouldn't fill the input or output apertures more than about 80% for a quality beam output.

At 10X this requires the beam expander to have an output lens of about 60mm wide to make sure no more than 80% of the collimation lens diameter is used, at least, for the slow axis going through it when using a three element lens on your pointer which has a bit wider beam output but when I think about this more, if you are going to use a beam expander anyway, why suffer the extra loss of a three element lens? I see no reason to use anything other than a low loss single element lens on your pointer when using a beam expander. I'd only use a three element lens if you are not going to expand the beam further, or perhaps together with beam correction optics such as a cylinder pair, if need be.

For the higher divergence and wider output beams of the newer high power diodes coming out today we really need a bigger lens than the standard 6mm diameter G2 and three element lenses we are using, I'd like to see a 8 or perhaps up to 12mm lens for our pointers but this would probably require a redesign of the axiz type of modules we mount our diodes in right now, but I expect in time we will have them.

Beam shaping! This diode produces a very wide rectangle spot!

Regardless of using a beam expander or not, beam shaping to equal-up the slow and fast axis divergences and beam thickness for each polarity is something else this diode needs, I believe RedCowboy has been working on that. Also, if you use a pair of cylinder lenses to make both polarities the same size so you get a square beam instead of a rectangle, through doing so the fast axis divergence is improved to more closely match that of the slow axis and won't require a beam expander to have 1.5 or less mRad of divergence, a sweet deal all the way around.

Note: I'm making an assumption of the FL of the 3 element lens in this baby, not all 3 element lenses used in our lasers have the same FL. I'm calling this a 7 watt laser, but most of these diodes safely put out closer to 6.8 watts the way we use them, and if this is a three element lens there is no way this laser is putting out that much power, perhaps closer to 6 watts. Although the loss of a G2 lens is less than a 3 element, the increased divergence doesn't make it worthwhile to me, so I will stick with this lens because I like putting spots on clouds, if used primarily as a burner, then the G2 lens would be the way to go.
 

Alaskan

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I bought an old soviet anamorphic projector lens from ebay, this one: Lot 2pcs LOMO Anamorphic Big Lens 35 Nap 2 3M 35KP 1 8 120 | eBay

The back section has what appears to be two biconvex lenses, that is what I used. The forward portion of the assembly which has the cylinder lenses in it isn't working out for me yet, I was hoping it would both correct the shape of the beam as well as expand it at the same time, it does, but the raw output from the diode isn't matching well with the focal length. I need to experiment with it more to get it to work right as a beam expander. However, the pre-section of lenses which couple with it sure focuses the beam down to a tight burning spot using the raw output from the diode, when held a few inches behind it.



I've taken the raw output of this diode before and focused it into a large 4 inch diameter PCX lens and had the same result, I could focus down to a tight spot from 6 to 20 feet away and burn holes in things very quickly. I could also adjust to infinity focus with the same lens and have a uber low divergence output, since the beam was expanded so much.
 

RedCowboy

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It would be nice to find an anamorphic lens that would do the job of 2 cylindrical lenses, but with 2 cylindrical lenses you can adjust the distance of each, the problem is the rapid divergence of these diodes, we need to get close to the emitter with the right anamorphic, one that is small but very powerful, almost aspheric anamorphic.....if I knew what I was doing I should be able to have some made.

 
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Alaskan

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I wish we could find an optical engineer who could help us, or perhaps we could ask one of the China manufacturers if they can both design and make them for us?

Here's a photo of the large 3 inch diameter camera lens assembly I used to focus the uncollimated output from a NUBM44 down to less than a quarter inch 15 feet away and this was at a 45 degree angle, so the true width if I had pointed straight on would have been half of that or less.

When straight on, the three element 6mm diameter lens (when fully collimated) used in this pointer produces close to a 1.25 inch wide stripe that far away, at the ~45 degree angle I took the burn photo at, closer to 3 inches wide. The ratio of a 3/16 wide burn mark (as in the photo) using the big 3 inch lens focused to a point to what a normal 6mm diameter three element lens produces at this distance and angle is a factor of 16 times smaller than normal.



The nice thing about using big lenses like this to collimate the output of a laser diode is it can be focused close in for a small burning point, or focused to infinity as an expanded beam for low divergence. Unfortunately expansion like this does not correct the beam to have equal sides, so you end up having a ribbon-like beam output at infinity focus, but that isn't really so bad, you can still put a nice spot on the underside of fairly high altitude clouds and even with unequal divergence for the two polarities, both sides are well under 1 mRad, even the fast axis tenths of an mRad.
 
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RedCowboy

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That's proof of concept.

I was getting excellent results with my NUBM06 and one of those 1 inch compounds from the 50 inch Hitachi in a slide zoon setup.

If we could get at FAC lens up close in a M9x0.5 screw in and use a thin lock ring to set it, then a G2 or G7 could focus a tighter squared up beam.
 

Alaskan

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I've tried to find a small FAC lens, was unable to find a place to buy one.
 

Alaskan

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I believe so, what kind of diode mount are you thinking of? C-Mounts might allow doing so but the lens would probably end up being shorter, if needing to be broken off. Maybe the glue could come off with the lens without breaking, but I wouldn't expect to be able to easily do so. I had a C-Mount with a FAC on it which had one end come loose from the diode inside a laser pointer, don't know how that happened. No longer have it though, never considered trying to salvage the FAC lens, it was so tiny.
 

RedCowboy

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With the NUBM44 the can window means we need a short FAC bigger than the C-mount uses because the beam will already be diverging where we can catch it, maybe 0.5 to 1mm from the can window.
It will have to be a purpose ordered lens from Edmunds, but I do not know how to calculate it.
It could be glued to a 0.5 - 1 mm thick 7 mm wide ring and that ring could be glued to the diode can....carefully with UV curing glue, but I wonder about diode can inconsistencies, we should be able get it close enough, the G9 lenses were glued to the cans, a small anamorphic or FAC that sets a best average beam would be good, then a shallow lens could be used to focus, the anamorphic could be designed to give slightly positive divergence then the adjustable screw in could do the focusing, we just want to shape the output while it's small.

The NUBM06 would be a better diode to work with, if we could get a replacement can that sat close to the emitter with our FAC attached we could glue it at the base and protect the emitter. Also the divergence of the numb44 is 33% more than the nubm06 and power is within 1 watt.
 
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