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Focus help! (ofc XD)

Norwayboi

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So Today I got my 2nd nubm08 diode. And this one actually had a decent focus. But not good enough. I want it the be a dot from far away (as close a possible at least). And like you can se on the photo it’s not a dot. It’s like the same length as my fingers. So question is. How do I get this focused? It’s a gball so yeah I know it’s not just, to put on a single g2 lens. I already tried putting g2 backwards and then another g2 to actually focus. But that doesn’t work. Any ideas? Beam expander with another lens maybe?
Picture taken about 4m away
 

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diachi

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Look up threads on beam correction. Relevant search terms: telescope, cylindrical lens pair, anamorphic prism pair. That might get you started.
 

paul1598419

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Since yours uses a ball lens it becomes a bit more complex. Cylinder lens pairs is what we use first, but only with a very well focused beam, then a beam expander will help in getting it down range, but you will never get a round dot out of these. Best way forward is to build one yourself or have one built for you.
 

Norwayboi

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Since yours uses a ball lens it becomes a bit more complex. Cylinder lens pairs is what we use first, but only with a very well focused beam, then a beam expander will help in getting it down range, but you will never get a round dot out of these. Best way forward is to build one yourself or have one built for you.
Ok thx 👌do you know where i can get my hands on a cylinder lens? On eBay its only Big ones.
And BTW. I have built it myself
 

steve001

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So Today I got my 2nd nubm08 diode. And this one actually had a decent focus. But not good enough. I want it the be a dot from far away (as close a possible at least). And like you can se on the photo it’s not a dot. It’s like the same length as my fingers. So question is. How do I get this focused? It’s a gball so yeah I know it’s not just, to put on a single g2 lens. I already tried putting g2 backwards and then another g2 to actually focus. But that doesn’t work. Any ideas? Beam expander with another lens maybe?
Picture taken about 4m away
A diode laser has two axis; a slow and fast. It is rectangular in shape. The slow axis is longer. The simplest solution is to slow the slow axis of the beam with one cylindrical lens. Doing so will create a square or nearly square beam shape which at great distance will look spotlike.
 
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paul1598419

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🍺Congratulations to Paul1598419 on the 16,000 LPF posts milestone 🍺
Thanks, Buddy. I just happened to notice that when it turned over. Hard to believe that many posts have passed.
 

Encap

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Thanks, Buddy. I just happened to notice that when it turned over. Hard to believe that many posts have passed.
Yes, hard to believe on just time required to do basis.
16,000 over 6 years is 2666 post a year.
That is an average of 7.3059 posts a day 365 days of the year of mostly LPF laser and laser related purpose not meaningless garbage chit chat 'social media' posts. Not easy to do.

Assuming 1 hour to do an average of 7.3 posts per day 365 days a year works out to 2190 hours of LPF posts over a 6 year period.
In USA a full time/8 hours a day work year is 2000 hours with 2 weeks vacation.... so you have put in more than a full time work year posting on LPF. 1 of last 6 years dedicated to posting on LPF om a full time work basis.
 
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paul1598419

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Geeze! when you put it like that it does sound like work. But, I have enjoyed all the new diodes that have come out, not to mention the new DPSS lasers too. Lots of information to gather and impart.
 

diachi

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A diode laser has two axis; a slow and fast. It is rectangular in shape. The slow axis is longer. The simplest solution is to slow the slow axis of the beam with one cylindrical lens. Doing so will create a square or nearly square beam shape which at great distance will look spotlike.
The slow axis is longer in the near field, not in the far field. The fast axis is what you expand with the cylinder lens pair, which reduces the divergence/increases the beam diameter to match that of the slow axis.
 

paul1598419

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The confusion exists in which is exactly the fast and slow axes. Geometrically, the fast axis is normal/perpendicular to the long side of the diode's face. Many people believe it is whichever axis that looks longer in the far field. This would be acceptable for most single mode diodes, but not multi-mode ones.
 

steve001

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The slow axis is longer in the near field, not in the far field. The fast axis is what you expand with the cylinder lens pair, which reduces the divergence/increases the beam diameter to match that of the slow axis.
To be certain we are on the same page here are two questions.
Which is the fast axis?
Which is the slow axis?
Some more.
Why would the slow axis not be longer in the far field?
Are you certain you would use two lenses two expand the fast axis?
 

diachi

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To be certain we are on the same page here are two questions.
Which is the fast axis?
Which is the slow axis?
Some more.
Why would the slow axis not be longer in the far field?
Are you certain you would use two lenses two expand the fast axis?

The fast axis is the one with the higher divergence. It starts out with a smaller diameter but diverges quicker, forming a line in the far field. The slow axis starts larger but has a lower divergence and thus forms the narrow side of the rectangle in the far field.

The slow axis is smaller in the far field because the divergence is significantly lower.

There's a reason it's called a cylinder pair. Not sure how you'd form a beam expander with one lens.

Due to that fast divergence, this is called the fast axis direction.
 




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