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M140 Beam Divergence Questions

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Sep 5, 2015
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I've always thought if you put a m140 diode in one of DTR's module and added a 3 element glass lens you would a round beam far away. As I continued to browse through the forums, ive noticed people posting pictures of a flat beam and taking about using prism pairs to make the beam rounder.

If I put the m140 diode in the 12*30 module and add a 3 element lens what beam pattern will I get? And if the pattern is flat, is there any way to correct it?
 



RedCowboy

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Jul 10, 2015
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I've always thought if you put a m140 diode in one of DTR's module and added a 3 element glass lens you would a round beam far away. As I continued to browse through the forums, ive noticed people posting pictures of a flat beam and taking about using prism pairs to make the beam rounder.

If I put the m140 diode in the 12*30 module and add a 3 element lens what beam pattern will I get? And if the pattern is flat, is there any way to correct it?
The M-140 is a multimode diode and the output comes out of a tiny PN junction behind that little glass window on the front of the diode.
It exits as a rectangle of light with one axis diverging ( spreading out ) faster than the other.
You can focus that with a lens such as the 3 element but it will still be a rectangle that you can focus to a tiny point/rectangle up close.
However the focal point/rectangle will be bigger the further away you focus it, but to the naked eye it looks pretty good.
However you will not have a dot, if you want a dot then use a single mode diode.
Now there are all kinds of optics and beam shaping methods but you will have to read and learn because it would take hours just to start explaining it all, but the first thing to understand is focal length, that is the distance between the PN junction and the lens, the longer your focal length the more accurately you can reproduce the initial output picture at a distance.
For instance if you wanted a focal point the same size as it exits a diode/source and you set a 10 power lens at 10 inches from the diode/source then you could reproduce the exit diameter/picture at 100 inches.
So using a tiny powerful aspheric lens 5 mm from the diode you can get a tight focal point at about a foot away and a point twice as wide at 2 feet away.
The divergence also influences the focus.
These diodes are highly divergent and more so on 1 axis than the other.
So using beam shaping optics to reduce divergence is the first step to correcting this output if you wanted to do all that.

As it is the M-140 with a 3 element makes a decent looking output that to the naked eye looks a lot like a beam and you can focus it up close and burn wood and such with it, BUT YOU MUST WEAR SAFETY GLASSES, that is glasses that attenuate the wavelength to protect your retinas because your eyes will be severely damaged if you don't.
It's similar to looking at a welders arc, you might think you saw one once and you did not go blind, but if you weld without eye protection you will go blind, also blue light is more dangerous to our eyes because the tiny light sensing parts don't protect themselves very well against blue light and that makes it even more dangerous. Then there are accidental reflections...do yourself a favor and just wear the safety glasses.

If you want numbers a M-140 with a 3 element lens focused as tight as you can get it at 15 feet makes a rectangle that is about 1.5mm by 8mm and it will burn a hole through a wet green leaf so be careful if there are houses people behind a stand of trees if you aim your laser that direction, just like a gun be aware of your backstop and do not allow anyone to be injured by your hand. Remember even at longer distances where the beam is wide, even though it cant burn it could distract someone say driving a car and know that pointing any laser at an aircraft is a serious felony with mandatory jail time and huge fines. So be very careful, just like you wouldn't throw a rock into traffic don't point a laser where it can harm anyone in any way.

I don't say this to be rude, I just don't know if you are 50 years old or 15 as all your profile says is you were born in July.
Here is a video I made of a m-140, I was wearing laser glasses.
https://www.youtube.com/watch?v=ISqseWYPw60
 
Last edited:

Pi R Squared

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May 14, 2013
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You can look at my M140 build with a 3 element lens here:
http://laserpointerforums.com/f65/assembled-m140-c6-pic-heavy-83543.html
Scroll down to the first and second beam shots to see the beam unfocused, that is the shape of the beam, the other beam shot photos are really no good because it's too bright for the camera and reflects off the camera lens. It does focus to a small spot so you can't tell its a rectangle but with the 3 element you will get some splash on both sides of the rectangle like this ( - ) but it's not too bad. Mine is driven at 1.5A and does 1.5W with the 3 element lens.

Alan
 

barthchris

Active member
Joined
Jul 9, 2009
Messages
152
Points
28
The M-140 is a multimode diode and the output comes out of a tiny PN junction behind that little glass window on the front of the diode.
It exits as a rectangle of light with one axis diverging ( spreading out ) faster than the other.
You can focus that with a lens such as the 3 element but it will still be a rectangle that you can focus to a tiny point/rectangle up close.
However the focal point/rectangle will be bigger the further away you focus it, but to the naked eye it looks pretty good.
However you will not have a dot, if you want a dot then use a single mode diode.
Now there are all kinds of optics and beam shaping methods but you will have to read and learn because it would take hours just to start explaining it all, but the first thing to understand is focal length, that is the distance between the PN junction and the lens, the longer your focal length the more accurately you can reproduce the initial output picture at a distance.
For instance if you wanted a focal point the same size as it exits a diode/source and you set a 10 power lens at 10 inches from the diode/source then you could reproduce the exit diameter/picture at 100 inches.
So using a tiny powerful aspheric lens 5 mm from the diode you can get a tight focal point at about a foot away and a point twice as wide at 2 feet away.
The divergence also influences the focus.
These diodes are highly divergent and more so on 1 axis than the other.
So using beam shaping optics to reduce divergence is the first step to correcting this output if you wanted to do all that.

As it is the M-140 with a 3 element makes a decent looking output that to the naked eye looks a lot like a beam and you can focus it up close and burn wood and such with it, BUT YOU MUST WEAR SAFETY GLASSES, that is glasses that attenuate the wavelength to protect your retinas because your eyes will be severely damaged if you don't.
It's similar to looking at a welders arc, you might think you saw one once and you did not go blind, but if you weld without eye protection you will go blind, also blue light is more dangerous to our eyes because the tiny light sensing parts don't protect themselves very well against blue light and that makes it even more dangerous. Then there are accidental reflections...do yourself a favor and just wear the safety glasses.

If you want numbers a M-140 with a 3 element lens focused as tight as you can get it at 15 feet makes a rectangle that is about 1.5mm by 8mm and it will burn a hole through a wet green leaf so be careful if there are houses people behind a stand of trees if you aim your laser that direction, just like a gun be aware of your backstop and do not allow anyone to be injured by your hand. Remember even at longer distances where the beam is wide, even though it cant burn it could distract someone say driving a car and know that pointing any laser at an aircraft is a serious felony with mandatory jail time and huge fines. So be very careful, just like you wouldn't throw a rock into traffic don't point a laser where it can harm anyone in any way.

I don't say this to be rude, I just don't know if you are 50 years old or 15 as all your profile says is you were born in July.
Here is a video I made of a m-140, I was wearing laser glasses.
https://www.youtube.com/watch?v=ISqseWYPw60
Great post! Good information here!:thanks:
 




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