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Collimation, What do people want to know ?

rog8811

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Thanks Pseudo, that makes things much clearer :)

Regards rog8811
 

Stone

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Since this topic is explaining basically what I would like to know, i'm going to ask in here... :)

I'm looking at expanding a beam as well, but from a basic laser pointer size beam (a Aixiz 650nm 10mw 12mm X 30mm case with a DVD burner diode) up to 40-50mm in diam. if that is possible. Is there expanders that would expand that much or is there some other way of doing it?
 

pseudonomen137

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Stone said:
Since this topic is explaining basically what I would like to know, i'm going to ask in here... :)

I'm looking at expanding a beam as well, but from a basic laser pointer size beam (a Aixiz 650nm 10mw 12mm X 30mm case with a DVD burner diode) up to 40-50mm in diam. if that is possible. Is there expanders that would expand that much or is there some other way of doing it?
Its possible, but can get expensive. I'm guessing that's somewhere in the range of a ~20-50x beam expander? You could buy one from a real optics joint, but it would be expensive as hell. One problem is that means you need at least a 50mm lens, and it would be wise to use a lens larger than the beam passing through it. If you wanted to go the DIY route though, you'd need a strong diverging or converging lens, and a large, weak, converging lens for the job. Check out the pictures above, one of them demonstrates the setup, and the formula that: |focal length of the second lens| / |focal length of the first lens| = how many times the beam will be expanded.
 

Stone

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Thanks for the reply :)

I was looking at this (I can't posts links - But it's a 50mm diam/35mm FL aspheric lens) to converge the beam after it had been spread, I just couldn't find anything that seemed suitable to diverge it though. The diverging lens needs to be able to spread the beam from it's original diam. to 40-50mm within the 35mm focal distance of the 2nd lens.

The beam doesn't need to be PERFECT, it's just a little project where i'd like to make up a Maglite housing and have a wide straight beam out of it.
 

Stone

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I have been using the formula above in the picture to estimate the lens I require... Since I can estimate the input beam diam, output beam diam, and the secondary lens I can rearrange the formula to work out the FL primary lens I need.

Since the output is d and the input is (f2 / f1) * d, I can call the input "y"... So I need to know f2.

y = (f2 / f1) * d
y / d = f2 / f1
(y / d) * f1 = f2

f2 = (2mm / 40mm) * 35mm
f2 = 0.05 * 35
f2 = 1.75mm

That seems like an unrealistic focal length for an aspherical or concave lens like in the above diagrams... Or is it possible?
 
L

likewhat

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That is a pretty small focal length. I found some that are 3.3 mm here

thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=16

although that would only give you a 21 mm beam.

1.75 mm might be something that is possible with a microscope lens or something. Unfortunately with a 35 mm that is what is needed to get your desired magnification.

There is a 3 lens system that uses a converging followed by a diverging followed by another converging lens that would allow you to create an arbitrary magnification within the size limitation of the lenses, but it would require more space. If you would like I can draw a picture of it and maybe that senkat guy can make it into a link you can click on.
 

steve001

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Stone said:
I have been using the formula above in the picture to estimate the lens I require... Since I can estimate the input beam diam, output beam diam, and the secondary lens I can rearrange the formula to work out the FL primary lens I need.

Since the output is d and the input is (f2 / f1) * d, I can call the input "y"... So I need to know f2.

y = (f2 / f1) * d
y / d = f2 / f1
(y / d) * f1 = f2

f2 = (2mm / 40mm) * 35mm
f2 = 0.05 * 35
f2 = 1.75mm

That seems like an unrealistic focal length for an aspherical or concave lens like in the above diagrams... Or is it possible?

Save yourself some headaches by using this applet
http://www.lightmachinery.com/gausbeam.php
If you are unsure how to use it I will help you through it

stone
I was looking at this (I can't posts links - But it's a 50mm diam/35mm FL aspheric lens) to converge the beam after it had been spread, I just couldn't find anything that seemed suitable to diverge it though. The diverging lens needs to be able to spread the beam from it's original diam. to 40-50mm within the 35mm focal distance of the 2nd lens.
Your not going to find any off the shelf lenses that will do that. It is highly unlikely you'll find a lens with a focal length < -6mm. It seems worldwide that -6mm negative focal length lens are the most common. And I must add to have a 4-5cm beam spread within 3.5cm would require multiple negative lenses.
 

Stone

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Thanks for the replies... It looks like I might have to resort to making my project a bit longer to keep the cost and availability of the lens easier to work with.

If we disregard my length limitations, is there any common and cheap lenses that would work for me? The only store i've looked at is Surplus Shed as their lenses seem quite cheap.

If I was to use the common -6mm FL lens mentioned, i'd need a 120mm FL secondary lens, that's 126mm between 2 aspheric or 114mm between a concave and aspheric. My secondary lens MUST be 50-52mm in diam.

Steve... I don't understand that beam program, just due to not knowing the terms "separation length" and "Rayleigh range", but I can do a search :)

[edit]
I've been Googling lens suppliers and i've found many small 2-3mm FL lenses from various suppliers but the prices seem rather expensive. As this is just project has no real use other than me wanting to make a wide beam, I don't really want to spend a fortune on it.
 

steve001

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Stone said:
Thanks for the replies... It looks like I might have to resort to making my project a bit longer to keep the cost and availability of the lens easier to work with.

If we disregard my length limitations, is there any common and cheap lenses that would work for me? The only store i've looked at is Surplus Shed as their lenses seem quite cheap.

If I was to use the common -6mm FL lens mentioned, i'd need a 120mm FL secondary lens, that's 126mm between 2 aspheric or 114mm between a concave and aspheric. My secondary lens MUST be 50-52mm in diam.

Steve... I don't understand that beam program, just due to not knowing the terms "separation length" and "Rayleigh range", but I can do a search :)

[edit]
I've been Googling lens suppliers and i've found many small 2-3mm FL lenses from various suppliers but the prices seem rather expensive. As this is just project has no real use other than me wanting to make a wide beam, I don't really want to spend a fortune on it.
In the two top boxes input 0.14
and 3 for the one below. these numbers are based upon a laser I have. This is the approximate beam diameter and beam divergence as it exits the crystal.


Focal lengths of the lenses can be any length.
First lens separation can any length. for this run through use 1mm
First lens focal length -6mm
Second lens focal length 20 mm
Second lens separation start with 20 mm
Decrease the distance of the 20mmEFL lens in 1 mm increments then in smaller increments

Repeat this procedure again, but this time change the 20EFL mm to 48mm. Start the second lens at 48 mm distance. Then start to decrease the distance 1 mm at a time then in smaller increments. Watch how the Rayleigh range increases dramatically. There will be a point where the beam is optimally collimated as indicated by the graphic display.

Now for the 3rd exercise add a second -6mm EFL lens with a
separation of 9mm from the first
Change the positive lens too 126mm EFL
repeat the same step as before until you
if you position the lens 121. 725 mm from the second negative lens you'll get a Rayleigh Range of 254451.824mm or 834.815696 feet


To know the beam expansion power divide the positive lens by the negative lens.

Beam Diameter at Surface means, beam diameter is at the positive lens

Rayleigh range is the distance over which the beam expandes the square root of 2 or 1.41 times it's initial diameter. Beyond that point the beam will expand linearly with distance.
 




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