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-   -   Knife edge followed by expander? Anyone try that here? (https://laserpointerforums.com/f49/knife-edge-followed-expander-anyone-try-here-94678.html)

Alaskan 08-12-2015 04:16 PM

Knife edge followed by expander? Anyone try that here?
 
I'm interested in building a knife edge for 4 diodes to be expanded to 50-80mm, anyone ever do thst here? Any recommendations for me? Appreciate your ideas and knowledge if you care to comment.

logsquared 08-12-2015 09:00 PM

Re: Knife edge followed by expander? Anyone try that here?
 
I would expand the beams first then knife edge. Otherwise you will end up with large gaps between the beams if you are trying to overlap the farfield spots. Expanding first will allow the beams to be converged at a distance with out the nearfield "gaps".

Alaskan 08-12-2015 10:11 PM

Re: Knife edge followed by expander? Anyone try that here?
 
Expand to 50-80mm first, too big to fit four in a pointer then :p

logsquared 08-12-2015 10:56 PM

Re: Knife edge followed by expander? Anyone try that here?
 
I would stack 2 beams on top each other then PBS another second set of two. This way you only have 1 "gap". Another thing to consider is the astigmatic beam may cause problems with a spherical expander when using multimode wide stripe diodes. not sure, never tried it with anything other than SM diodes.

Alaskan 08-12-2015 11:46 PM

Re: Knife edge followed by expander? Anyone try that here?
 
Hummm... if I understand correctly, here's what I'm seeing: knife edge two diodes each as separate knife edge paths which are then shot into a PBS cube to combine all four through the cube. That's an interesting approach. I'm still learning and a long way to go on such things.

Edit: Found an image

http://i.imgur.com/B5Bdb.png

Benm 08-13-2015 12:57 AM

Re: Knife edge followed by expander? Anyone try that here?
 
If you set it up as pictured above the output pattern would be a + sign, with or without gaps in the horizonal and/or vertical parts of the + depending on how well things are aligned.

If you want t do any correction for beam shape you must do so before the combining cube. After that, the fast and slow axis of both banks are intermingled and cannot be corrected for using things like prism pairs.

Alaskan 08-13-2015 01:28 AM

Re: Knife edge followed by expander? Anyone try that here?
 
OK, I can do beam correction before the PBS, if I do beam correction at all & I don't mind a cross pattern so much. I want to expand the beams to make a large 50-80mm wide thick beam output to reduce the divergence. Thinking on how to reduce the number of mirrors, I came up with this, what do you all think?

http://i853.photobucket.com/albums/a...oject/87_1.jpg

Sorry, my skills at drawing graphics are terrible.

If the expanded output is a cross pattern or has some gaps it isn't so important to me, I'm just after a high power beam output, of what ever shape as long as the divergence is uber low. Small gaps are ok, but the less the better, of course.

I want to put this all inside a pointer like this one, below:

http://i853.photobucket.com/albums/a...ps2rdffrum.jpg

http://i853.photobucket.com/albums/a...psysyvcyvd.jpg

http://i853.photobucket.com/albums/a...psvlsvihdn.jpg
This photo is of a pointer with a single NDG7475T 1W diode in it expanded to 50mm. The three element lens used is adjusted out of focus so the spot covers the diameter of the 2 inch/50mm lens which then collimates to infinity.

Benm 08-14-2015 01:09 AM

Re: Knife edge followed by expander? Anyone try that here?
 
If you want a high-diameter, low-divergence beam you should probably forget about the whole PBS idea and just use all laser diodes on one polarisation plane.

You could knife-edge them so the fast axis are all next to eachother, resulting in a line-like output pattern where the outputs of the lasers overlap at larger distances. This could then be fed through a prism pair to reduce the difference in divergence between directions, followed by a beam expander.

The PBS cubes are good for combining the output of 2 single mode lasers, but not really good for combining the output of several multimode, knife-edged, arrays - unless you did the prism pair correction before combining. Doing so would make it hell to align though.

Alaskan 08-14-2015 03:52 AM

Re: Knife edge followed by expander? Anyone try that here?
 
OK, that sounds good to me, I have some 1/2 inch Newport MM-050-HEX kinematic adjustable mirror mounts on the way. I bought some flex mounts too as an option, but they are larger, would rather keep things smaller due to using these very small 9mm diode mounts: https://www.lasertack.com/en/laser-diode-mout - Although I have some concerns regarding their heat transfer characteristics with the anodized aluminum, any idea if that affects it for surface to surface coupling to a heat sink? I've done some googling and it appears anodized surface may actually enhance the heat transfer, but not completely sure, it certainly does to the air for increased radiation and seems reasonable to assume it may help for joints too.

CDBEAM777 08-14-2015 01:03 PM

Re: Knife edge followed by expander? Anyone try that here?
 
Quote:

Originally Posted by Benm (Post 1374414)
If you want a high-diameter, low-divergence beam you should probably forget about the whole PBS idea and just use all laser diodes on one polarisation plane.

You could knife-edge them so the fast axis are all next to eachother, resulting in a line-like output pattern where the outputs of the lasers overlap at larger distances. This could then be fed through a prism pair to reduce the difference in divergence between directions, followed by a beam expander.

The PBS cubes are good for combining the output of 2 single mode lasers, but not really good for combining the output of several multimode, knife-edged, arrays - unless you did the prism pair correction before combining. Doing so would make it hell to align though.

Alak....See the Tridentis build !!! http://laserpointerforums.com/f65/tr...uty-83781.html Three (3) 9mm 445 diodes....Knife edged...

So ...in this build, the beam output is like .......... lll

But....they are so close, one cannot see the gaps...then put thru a set of Anamorphic prism's to reduce the spread....and achieve a better X = Y aspect ratio....not perfect...but better !

So....after this type set up....then you could run the three (3) beams thru the beam expander !! But...after the expander...you may see the gaps appear....for the expander....well...it expands the beams....and the gaps !! Aren't optics fun !!

Oh....And you can knife edge four (4) beams...side by side...no problem....It is mainly a matter of how much room you have to work with....which comes down to how big you are willing to allow the build to get !!.....IMNSHO...Four (4) beams...knife edged side by side will require a slightly longer build...but...doing an "L" shaped arrangement....with two (2) beams knife edged and an additional two (2) beams coming in at 90 degree....you can also do this....but...this will result in a slightly wider build !! So...each arrangement has it's issues !!

And remember.....when u shoot the Moon....the beams....on the Lunar surface will show that one cannot achieve perfect alignment between the beams....HAHAHAHAHA

Alaskan 08-14-2015 02:50 PM

Re: Knife edge followed by expander? Anyone try that here?
 
I like it, thanks :)

What do you think of using these cylinder lenses to correct the output instead of anamorphic prims?

Cylindrical lenses 520 nm - Opt Lasers

CDBEAM777 08-15-2015 01:50 AM

Re: Knife edge followed by expander? Anyone try that here?
 
For some reason....I have decided the Anamorphic Prism's are the best to use on the 9mm 445 LD.

Now....I have no experience with trying to correct the high power multimode green @ 520nm.... ???

I do know the Opt Laser Cylindrical's are about 3.5X for the magnification. If they will correct the Green multimode...I do not know.

I am about to buy the NDG 700.....so....I will experiment then .

Alaskan 08-15-2015 03:25 AM

Re: Knife edge followed by expander? Anyone try that here?
 
PM me, I know a seller for the NDG7475T for 200 USD

Benm 08-16-2015 01:00 AM

Re: Knife edge followed by expander? Anyone try that here?
 
The reason for using prism pairs instead of round optics is fairly simple in this case:

The diode as an output pattern that resembles a narrow line, which at a distance through regular optics becomes a wide line perpendicular to that narrow line. Prism optics only correct in one direction while round lenses correct in all directions at the same time.

What you are actually doing with a prism pair is building a beam expander that only acts in the direction the line output is narrow in. The goal is to expand the beam in that direction to match the other axis resulting in a more or less square beam profile at large distance.

Alaskan 08-16-2015 03:53 AM

Re: Knife edge followed by expander? Anyone try that here?
 
I have a prism pair taken out of some UV equipment which doesn't seem to have a coating, I will compare them at some point and see what happens.

Bionic-Badger 08-17-2015 11:42 PM

Re: Knife edge followed by expander? Anyone try that here?
 
Another thing you could do is just stack up the knife edging only in the narrow axis, achieving a stack 50-80mm tall, and then correct the beam with cylindrical optics + prism pairs in the wide axis to form a "square" beam of the target size.


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