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OPT Lasers Cylindric lenses - NUBM44 beam correction tests

RedCowboy

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Hello,

Long time I was not here. Overal efficiency of this lens is 99,7% sometimes even better. Using two lens it is 99,4% quaranteed. We payed quite a lot for this coating.

I don't see any 6x pairs on your site, do you have any?
 



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No only 3x and 2x.
Combining 3 lens you can make 6x.
If I had kind of order for 20 pairs I could arrange the production of 100 pairs.
 

CDBEAM777

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LSG....just saw your post....sorry.....thanx for your info ....great link !!! After all....I completely admit...I am just an " Optical Engineer Wannabee " :san: But...I truly enjoy the path of learning !!!


Beam out





QUOTE=Light superglue;1421089]Hi Milos,

I am happy that your idea is working. I soon will finish a device with 2 PBSed 07e and a similar set at the end.


BTW CDBEAM, I once calculated the Raypath with a program from one of Alaskan´s posts, here is citation:

"According to this program, you can get 7.5x expansion with 3 lenses from 3x sets (at assumption that focal lenths are -10 and 30mm the lens separations will be 5 and 24mm to get collimated beam).

https://lightmachinery.com/optical-d...yUaPB1sc6rdN2w

If lens separations are 20 and 22.5mm the expansion will become 12x."

Maybe 4x works better because lower glass thickness allows for concave curvatures to be closer?[/QUOTE]
 
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Light superglue

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Hi CDBEAM, I am also "just a chemist" working as an engeneer sometimes, so have to learn from trial and error all the time. That program looks perfect at assumption that lenses have zero thickness, what is far from truth in real life, but as theory tool we can get some ideas playing with it.
E. g. based on it I would like to try focusing at different range several beams which would be not perfectly knife edged but would at least lay in one plane simply by playing with CL separation. This could upgrade styropiro shotgun and make it like a device RC planned with rangefinder avoiding the need to motorise many "rotating mirrors"...

Hi Mateusz, would it be possible to make a ONE GLASS PIECE 6x or 9x cylindrical expander with CC and CX surfaces thick enough to replace 2 lenses or too difficult for "stand of the art" at the moment? In this way we would only need 2 surfaces coated, not 4.
 

RedCowboy

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malford

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With my NDG7475, using DTR three element lens and OPT 2x cylindricals, at 15 feet from the aperture the beam is about 4.75mm wide. At 28 feet, it is about 8mm wide. Using the calculator here, this comes out to about 0.76 mrad. The reason I started measuring at 15 feet instead of any closer is that the beam begins as a vertical line, becomes a squarish shape around about six feet, then started turning into a horizontal line after that. I was driving the diode with about 0.6 amps for the measurements.

In the image below, you can see the beam starts off as a narrow vertical line. By the time it impacts the second cylindrical lens, it is twice as thick and still vertical. Everything makes sense so far.


In the image below, you are seeing the beam spot at about 28 feet from the aperture. It is now a horizontal line. Initially, the cylindrical lenses expanded the narrow axis. But, that axis is now the wide axis at the end of the beam. What is really vexing to me is that when I remove the cylindrical lenses, the wide axis at the end of the beam is wider. This doesn't make sense with my limited laser and optics knowledge.
 

RedCowboy

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All MM diodes do that with a 3 element, G2, any lens the initial wide becomes the narrow as it's the narrow that diverges rapidly becoming the wide.

With a G2 I actually have mine run negative, or converge to about 7 feet then diverge again.

This is a nubm06 but you can see it shrink then re expand. I say 1/4 by 1/4 in the video, but I mean it's under a 1/4 by 1/4

But the shape of the emitter being a rectangle turns 90 degrees at a distance because the narrow part is the rapidly diverging axis.

Granted the 06 is about twice as divergent as the NDB7875 and NDG7475, the NUBM06 is much like the NDB7A75 producing a line width twice that of the 7875/7475 at any given distance.

If you lifted out your 2nd cyl lens the convex lens your line would be around 18 inches wide at 15 feet. Well if you are using a 3 element it will be less but still very wide. Point is that narrow initial axis diverges faster regardless. You know the cylindrical pair is just a 1 axis expander set.

 
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malford

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My goal is the continue correcting the beam as much as is physically possible. Considering the fact that my beam is still considerably wider than it is tall, jumping from a 2x to 4x cylindrical set seems fitting. Would you agree?

Once the beam is square/round I'd like to add a two dimensional expander to reduce the overall divergence. I don't want to go so large that I lose the crispness of the beam at shorter distances. A 4x ratio seems fitting. Would you agree?

I'm considering purchasing from Edmund Optics. How do you think this would compare to the divergence that you achieved?

12mm H x 25mm L x -25mm FL MgF2 coated cylindrical lens
12mm H x 25mm L x 100mm FL MgF2 coated cylindrical lens

25mm DIA x -25mm FL MgF2 coated plano concave lens
25mm DIA x 100mm FL MgF2 coated plano convex lens
 

RedCowboy

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That sounds expensive, why not get rid of that 3 element and use a DTR G2 lens and your 2x or 3x cyl pair from opt and a Jet Lasers 10x expander or a SANWU 3.3 x expander.

I tested the 3 element and G7 prior to cyl pair shaping and the G2 is the much better way to go, you pick up the beam at a much tighter size with the G2 and get most all your power as well and it's a lot cleaner.

It might seem like the 3 element would be a good choice but it's not, you want the G2.

This is an early test with a NUBM44 that has 300% the divergence of the NDB7875/NDG7475 at about 4 meters.
The G2 worked better than the 3 element, I cant find my 3 element pics but here's the G2, but remember this is a very divergent diode and I used a 6x pair, you can see the before and after with the cyl pair, but with a 3 element results were not good, the beam size into the cyl concave was larger with the 3element and that ends up being counter productive.

It's hard to see but the tighter starting beam means a tighter exit beam, with the 3 element it works backwards than we would think, I would try a DTR G2.





 

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malford

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The three element gave me the tightest spot out of the following collimators that I have tried:

DTR G2 (Won't screw far enough into my OPT TO-5 brass diode housing to focus)
DTR three element
OPT three element
OPT single lens
Sanwu G7 (hasn't arrived yet, will test when it does)

A pair of 25mm lenses from Edmund to create a 4x expander is only $69. With this option, I know exactly what I am getting with all the datasheets they provide.. The lenses have 1.25% reflectance at 520nm, MgF2 coating, etc. The expander from Sanwu is 60$ and has no data on anything. Who knows what the surface quality, coating, reflectance, max power density, etc. is?
 

RedCowboy

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Try it again and back it out to see if you went too far, it's very touchy, a fraction of a rotation changes everything so you can easily go past focused and it will seem like it wont go far enough, you may have just gone past it.

DTR's G2 is a 2.39mm rear focal length single element, but SAWNU/Podo's G2 has a concave rear input and focuses further out, There is more splash but it works and makes a tight beam, it's actually the lens in my 75 foot burner.

They are only 10 dollars and a cool looking lens, set your concave cyl very close to it after you focus to infinity, the beam will be needle tight close to it's exit and that's what you want.

See how close I set mine.



PODO'S/SANWU G2 it's 8 dollars or 10 dollars in the holder GET IT IN THE HOLDER. p.s. It doesn't need the O rings, it's a good fit without them, better than the others, virtually zero lens thread slack.



 

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steve001

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The three element gave me the tightest spot out of the following collimators that I have tried:

DTR G2 (Won't screw far enough into my OPT TO-5 brass diode housing to focus)
DTR three element
OPT three element
OPT single lens
Sanwu G7 (hasn't arrived yet, will test when it does)

A pair of 25mm lenses from Edmund to create a 4x expander is only $69. With this option, I know exactly what I am getting with all the datasheets they provide.. The lenses have 1.25% reflectance at 520nm, MgF2 coating, etc. The expander from Sanwu is 60$ and has no data on anything. Who knows what the surface quality, coating, reflectance, max power density, etc. is?
Look at their VIS 0 lenses. I recall the reflectance per surface will be less than 1.25% and can be a low as .4% per surface. Look at their listings for AR coated pcv and pcx lenses you'll see a pricing sweet spot.

If you have a ruler measure the effective focal length for the G7 lens would please and let me know. Convert to millimeters if you can or just give the figure and I'll convert it.
 
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RedCowboy

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The G7 finds it's focus out near the end of the standard 12mm module and the exit beam diameter is large, 7mm wide beam at exit, the rear FL is around 8mm. Thts in the 5mm long housing, in the 9mm long housing it clips some extra.

G2 rear FL is 2.39mm
3 element is 5.2mm or there about, there has been some deviation in manufacturing it seems, but some may just rattle loose in transit, but the 3 element clips 30% and is a compromise for quick easy use.

If you can do what you want with good optics then go for it, but the 3 element is just a compromise lens and a 30% power pig as it clips the divergent axis, so much that you can feel it get hot in seconds when used on the nubm44, you really want to get a G2 in there then use shaping optics on the fast axis.

The G7 is not as wasteful as the 3 element but not as good as the G2.
 
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malford

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I agree, 30% wasted power is unacceptable. Once I'm finished with the corrective optics, I'd like to examine the initial collimator optics. If I wanted to build a collimator from scratch, I assume I'd need to look into aspheric lenses, correct?

Further, once I have perfected this setup and acquired the perfect beam, I'd like to add a second NDG7475 and combine beams. My concern is that to get them to both pass through the PBS cube, one will need to be rotated. This means the beam profiles will be different and diverge unevenly. Is it possible to use a 90 degree wave rotator so that I can leave both diodes orientated the same direction to perfectly overlap beams, but still allow them to pass through the PBS because one will now be rotated?

Edit:
I looked into those VIS 0 lenses. Wow! 0.15% reflectance for green lasers. Under 0.2% for just about all of 400-700nm. It's only a few more dollars than the MgF2 I was looking at. But, the catch is that they have half the energy density limit as MgF2 at 5 J/cm2 vs 10 J/cm2. I would need to do some calculations to see what one of these laser diodes puts out in those units. Does anyone already know?
 
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steve001

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I agree, 30% wasted power is unacceptable. Once I'm finished with the corrective optics, I'd like to examine the initial collimator optics. If I wanted to build a collimator from scratch, I assume I'd need to look into aspheric lenses, correct?
I don't think so. All of the schematics I've seen for Galilean beam expanders mostly use two lenses. One a negative pcv, the other a positive pcx. Occasionally you'll see a beam expander with two lenses cemented together or spaced very close together. What's your application for the beam expander? One thing to keep in mind is to make sure the pcx lens has a diameter large enough so it does not truncate the sides of the beam as the beam passes through it.

What's nice about Edmund Optics is they carry a large number of in stock AR and non AR coated lenses.
 




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