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Focusing vs Collimation - Laser Performance
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Athoul
Wicked Lasers God
Joined: 13 Sep 2005
Posts: 7503
Location: Canada
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 Posted: 7/04/06, 8:08 AM Post subject: Focusing v |
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Focusing vs Collimation and how it effects laser performance.
First questions that this might relate to.
I have an 100mW Pulsar but can't pop balloons at X distance, yet I've heard some people can?
I have an 150mW Pulsar but can't pop balloons at X distance, yet I've heard some people can?
I have an XmW Laser but can't pop balloons at Z distance, yet I've heard some people can?
I have an XmW laser but can't light matches at as far a distance as I've heard from others with the same laser?
Before returning your laser and thinking it is defective, consider the following.
Assuming output is the same on both units, one must consider wether or not the beam is being focused or collimated.
Focusing means that the beam is getting smaller in diameter as it travels until the rays cross. The beam then expands again after this point.
Collimation is the result of making the beam remain as parrallel as possible. Because collimation is not perfect it is measured in mRad(milliradians). The smaller the number the less the beam expands over distance.
What does all this mean?
Simply put, it means that a laser which is focusing at a distance of say 20 meters will perform tricks within that distance much better then one that is collimated. This is because the beam is getting smaller in diameter up until the 20 meters, which it then again starts to expand.
This may explain why some Pulsars and other lasers are popping balloons as great distances while others of the same model are not. So again, before returning your laser as defective, take the time to find out if the beam is collimated or focusing.
_________________
Cheers,
Sean.
Visit My Laser Gallery for images, video's, comparisons and more. http://www.pulsed.ca
Some videos I have submitted:
http://www.lasercommunity.com/movi_page.php?movis_id=78
http://www.lasercommunity.com/movi_page.php?movis_id=77
http://www.lasercommunity.com/movi_page.php?movis_id=76
http://www.lasercommunity.com/movi_page.php?movis_id=84
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Gadgeteer
Wicked Lasers God
Joined: 30 Jan 2006
Posts: 2304
Location: North Texas
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| Posted: 7/04/06, 2:03 PM Post subject: |
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Good info! This was very much needed, thank you Sean.
Laser wise, for the pen style units, you also need to consider the construction of the device.
Pulsar-
bare diode (5.6mm can) that has a spread / divergence of 10 degrees on one axis, 30 degrees on the other (typical). I don't know if the focusing lens is a single element or a group but single is typical as with ANY red laser pointer. Collimation is not the correct term when addressing a red pointer, focus is the correct term. This should be clearly obvious that the beam is almost a 1/4" (close!!!) coming out of the laser but a far smaller spot at 30' away.
Greens-
not much different and beam divergence should be referenced to what is coming out of the crystal assembly rather than after the optical train. The beam from the crystal set does diverge quite a bit and is typical of very short resonator cavities, the YV04 (laser medium) is on the order of 0.5mm or so, KTP around 2-3mm, so divergence will be large.
This is sent through a reverse Galilean telescope to make for a tight and focused beam. This telescope system is common on virtually all green lasers of the pen style and others. It consists of a diverging lens mounted right after the KTP (beam exit from the crystal) and a focusing lens afterward. An infrared cut filter is typically mounted on either the diverging lens or near the focusing lens to filter out any stray 808nm pump light and 1064nm that may be emitted.
For the greens, if the beam is not centered in the end cap hole, this is due to improper positioning if the diverging lens and the slightest adjustment will throw the alignment off greatly. Correcting that issue is easy but takes a great deal of patience.
Spot size in the distance can be adjusted with moving the focusing lens. Moving the lens away from the laser brings the focus closer, lens towards the laser pushes the focus further out in the distance. There is a point though that beyond focusing the beam to infinity that the beam simply diverges.
Smaller far field spot sizes can be achieved by replacing the output/focusing lens with one of longer focal length. Common stock lens are around 20mm in focal length. Replacing that lens with one of 50mm focal length will GREATLY reduce the spot size in the distance when adjusted properly. This is also what would permit one to pop balloons at greater distances as the beam is concentrated to a smaller size. Replacing the output lens with one of longer focal length does have the drawback that the lens now needs to be positioned further from the laser. Replacing the stock 20mm for a 30mm on the Fusion required a 7mm spacer to be added, this is with the lens mounted in the endcap.
There seems to be much confusion in regards to collimation and focusing. I'm to lazy to break out the big books and read the law on the matter but I believe focus it the proper term when considering these systems based on the design. Greens do have what is called an "up-collimator" so that does count for collimation.
Power meters or some simple and inexpensive measurement in due and something several of us are working on. The LED trick is not reliable. Stay tuned for further info on that one.
JD
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http://gadgeteer.home.pipeline.com/laser/laser.htm
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lazerlit
4.99mW Green Laser Toy
Joined: 13 Sep 2006
Posts: 3
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| Posted: 9/13/06, 6:46 AM Post subject: Thanks |
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Thanks for the post!
This was very helpful |
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Sprtdude91
Elite Laser
Joined: 30 Oct 2006
Posts: 156
Location: Walled Lake, Michigan
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| Posted: 10/30/06, 7:24 PM Post subject: |
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| Gadgeteer wrote: |
Good info! This was very much needed, thank you Sean.
Laser wise, for the pen style units, you also need to consider the construction of the device.
Pulsar-
bare diode (5.6mm can) that has a spread / divergence of 10 degrees on one axis, 30 degrees on the other (typical). I don't know if the focusing lens is a single element or a group but single is typical as with ANY red laser pointer. Collimation is not the correct term when addressing a red pointer, focus is the correct term. This should be clearly obvious that the beam is almost a 1/4" (close!!!) coming out of the laser but a far smaller spot at 30' away.
Greens-
not much different and beam divergence should be referenced to what is coming out of the crystal assembly rather than after the optical train. The beam from the crystal set does diverge quite a bit and is typical of very short resonator cavities, the YV04 (laser medium) is on the order of 0.5mm or so, KTP around 2-3mm, so divergence will be large.
This is sent through a reverse Galilean telescope to make for a tight and focused beam. This telescope system is common on virtually all green lasers of the pen style and others. It consists of a diverging lens mounted right after the KTP (beam exit from the crystal) and a focusing lens afterward. An infrared cut filter is typically mounted on either the diverging lens or near the focusing lens to filter out any stray 808nm pump light and 1064nm that may be emitted.
For the greens, if the beam is not centered in the end cap hole, this is due to improper positioning if the diverging lens and the slightest adjustment will throw the alignment off greatly. Correcting that issue is easy but takes a great deal of patience.
Spot size in the distance can be adjusted with moving the focusing lens. Moving the lens away from the laser brings the focus closer, lens towards the laser pushes the focus further out in the distance. There is a point though that beyond focusing the beam to infinity that the beam simply diverges.
Smaller far field spot sizes can be achieved by replacing the output/focusing lens with one of longer focal length. Common stock lens are around 20mm in focal length. Replacing that lens with one of 50mm focal length will GREATLY reduce the spot size in the distance when adjusted properly. This is also what would permit one to pop balloons at greater distances as the beam is concentrated to a smaller size. Replacing the output lens with one of longer focal length does have the drawback that the lens now needs to be positioned further from the laser. Replacing the stock 20mm for a 30mm on the Fusion required a 7mm spacer to be added, this is with the lens mounted in the endcap.
There seems to be much confusion in regards to collimation and focusing. I'm to lazy to break out the big books and read the law on the matter but I believe focus it the proper term when considering these systems based on the design. Greens do have what is called an "up-collimator" so that does count for collimation.
Power meters or some simple and inexpensive measurement in due and something several of us are working on. The LED trick is not reliable. Stay tuned for further info on that one.
JD |
I don't understand this part under Pulsar could you explain it a little more please??????
"This should be clearly obvious that the beam is almost a 1/4" (close!!!) coming out of the laser but a far smaller spot at 30' away." |
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chargerman
Wicked Lasers God
Joined: 08 Sep 2005
Posts: 1721
Movie(s): 2
Location: Big Horn Mountains, Wyoming
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Sprtdude91
Elite Laser
Joined: 30 Oct 2006
Posts: 156
Location: Walled Lake, Michigan
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| Posted: 10/30/06, 8:50 PM Post subject: |
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| thanks that helped a lot! |
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chargerman
Wicked Lasers God
Joined: 08 Sep 2005
Posts: 1721
Movie(s): 2
Location: Big Horn Mountains, Wyoming
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Vic
Wicked Lasers God
Joined: 30 Oct 2006
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Picture(s): 66
Movie(s): 3
Location: United States, CA, Los Angeles
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