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Beam expander to focus laser beam

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Rintec

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My project is to make a laser beam expander so that a laser beam can be focused far away from the source.
I have read some sources on the internet but it ended up in "collimate the laser".
For example galilean telescope.
What I need is not just collimating, but to focus laser beam (waist become smaller then the original) at a distance. And not at the focal length of single lense.
I mean the focus should be adjustable between certain distance ~ infinity (collimate). Let us say from 10m ~ infinity.

I am a newbie. If there is a complete tutorial or simulation program it would be easier for me.
 
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Alaskan

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Re: Beam expander to focus laser bearm

This is a question I would like answered too, how far can we focus the beam of a laser using a large lens, and how large does it need to be for given distances. One of the reasons I ask is this, if a beam is fully collimated, the beam will still diverge at some mRad rate of expansion, but if focusing the beam to a spot, it is converging, not diverging. How far away can I converge a spot from the lens? Is the relationship related to lens diameter and focal length? If so, what is the relationship to diameter and focal length to be able to focus into a spot in the far distance?
 
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Rintec

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Re: Beam expander to focus laser bearm

Alaskan said:
This is a question I would like answered too, how far can we focus the beam of a laser using a large lens, and how large does it need to be for given distances. One of the reasons I ask is this, if a beam is fully collimated, the beam will still diverge at some mRad rate of expansion, but if focusing the beam to a spot, it is converging, not diverging. How far away can I converge a spot from the lens? Is the relationship related to lens diameter and focal length? If so, what is the relationship to diameter and focal length to be able to focus into a spot in the far distance?
Click to expand...

I found this literature very interesting but failed to understand deeply the mathematical expression.
http://www.telfor.rs/telfor2005/radovi/OT-6.3.pdf

Hope you can understand this and teach me back. Best regards.
 
lasersbee

lasersbee

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Re: Beam expander to focus laser bearm

Rintec said:
whew..it was a bunch. Thank you! I am reading on it.
Click to expand...

Rintec said:
I found this literature very interesting but failed to understand deeply the mathematical expression.
http://www.telfor.rs/telfor2005/radovi/OT-6.3.pdf

Hope you can understand this and teach me back. Best regards.
Click to expand...
I know that you are new here....
Double posting within a short time is
frowned upon my the Forum community.

You can easily Modify or Edit your posts
by using the [EDIT] button at the bottom
right of any of your posts.


Jerry
 
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steve001

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Re: Beam expander to focus laser bearm

Rintec said:
My project is to make a laser beam expander so that a laser beam can be focused far away from the source.
I have read some sources on the internet but it ended up in "collimate the laser".
For example galilean telescope.
What I need is not just collimating, but to focus laser beam (waist become smaller then the original) at a distance. And not at the focal length of single lense.
I mean the focus should be adjustable between certain distance ~ infinity (collimate). Let us say from 10m ~ infinity.

I am a newbie. If there is a complete tutorial or simulation program it would be easier for me.
Click to expand...
Make a Galilean beam expander. Purchase some plano-concave and plano-convex lenses with different focal lengths. Now experiment.
 
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steve001

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Re: Beam expander to focus laser bearm

Alaskan said:
This is a question I would like answered too, how far can we focus the beam of a laser using a large lens, and how large does it need to be for given distances. One of the reasons I ask is this, if a beam is fully collimated, the beam will still diverge at some mRad rate of expansion, but if focusing the beam to a spot, it is converging, not diverging. How far away can I converge a spot from the lens? Is the relationship related to lens diameter and focal length? If so, what is the relationship to diameter and focal length to be able to focus into a spot in the far distance?
Click to expand...

Other than using a lens whose diameter does not truncate the beam the important variable is the lens focal length. Without resorting to math, an easy way to determine lens diameter is to place a negative lens in the beam's path and measure the diameter in millimeters at various distances. That will give the minimum lens diameter: of course you'll want a lens that is some percentage larger say 5-10%.
 
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Alaskan

Alaskan

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Re: Beam expander to focus laser bearm

We need an optics guru for this one, I'm not at all sure how to focus a beam to a small spot at a great distance, I can use a normal beam expander which is adjustable to focus to a spot 30 feet out to burn nice holes in plastic, if using enough power, but I don't know if it is possible to focus a beam to a tiny converging spot a mile away, for example. How far away do you want to focus the spot?
 
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steve001

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Re: Beam expander to focus laser bearm

Alaskan said:
We need an optics guru for this one, I'm not at all sure how to focus a beam to a small spot at a great distance, I can use a normal beam expander which is adjustable to focus to a spot 30 feet out to burn nice holes in plastic, if using enough power, but I don't know if it is possible to focus a beam to a tiny converging spot a mile away, for example. How far away do you want to focus the spot?
Click to expand...

Have you seen this video? Laser burning at 300 feet
https://youtu.be/_9QotAtxrmc

In order to do that at a mile away you'll need a long long focal length lens.
 
Hemlock_Mike

Hemlock_Mike

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Re: Beam expander to focus laser bearm

Another question --- Does a low or high magnification
expander design make a big difference. It seems a 10x
is more sensitive than 3x in focus.
HM
 
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Singlemode Laser

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Re: Beam expander to focus laser bearm

steve001 said:
Have you seen this video? Laser burning at 300 feet
https://youtu.be/_9QotAtxrmc

In order to do that at a mile away you'll need a long long focal length lens.
Click to expand...


First, it is not possible to put the waist at infinity. For a given beam diameter and focal length of a lens, there is a maximum distance for the waist and after this the beam is divergent everywhere after the lens.

To achieve a minimal waist one needs a lens with a short as possible focal lenght. To achieve a maximal distance one needs a lens with a long as possible focal lenght. You can't have both at the same time.

@ Thread starter: What is your goal?

Singlemode
 
Alaskan

Alaskan

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Re: Beam expander to focus laser bearm

All good stuff, wish I knew. I read the links RCB provided earlier too and am late responding to this thread. Still, I can't find the answer to what is needed to focus a beam into a small burning spot a very long way away, but intuitively I'm guessing a very large diameter lens or parabolic mirror. Steve, when stating a long FL lens is needed, I bet a small diameter long FL lens won't do the job well, maybe a very large diameter long FL lens?

The reason this is interesting to me is I've wanted to do the same thing, focus my beam to converge at a great distance away instead of set to infinity focus which will just diverge at some rate of mRad. If you had a large enough diameter lens with a long enough FL, I'm betting that would do it but have no theory or math to confirm this idea. Google is my friend, I'll be asking.
 
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Singlemode Laser

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Re: Beam expander to focus laser bearm

Hemlock_Mike said:
Another question --- Does a low or high magnification
expander design make a big difference. It seems a 10x
is more sensitive than 3x in focus.
HM
Click to expand...

To have the same sensitivity the 10x expander should be about 3 times (10/3) longer than the 3x. This obviously not the case, so its is more sensitive. Make it longer (longer focal length lenses) reduces the sensitivity.

Singlemode
 
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steve001

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Re: Beam expander to focus laser bearm

Hemlock_Mike said:
Another question --- Does a low or high magnification
expander design make a big difference. It seems a 10x
is more sensitive than 3x in focus.
HM
Click to expand...

What do you mean by:" big difference"? What do you mean by: "is more sensitive"?


Singlemode Laser said:
First, it is not possible to put the waist at infinity. For a given beam diameter and focal length of a lens, there is a maximum distance for the waist and after this the beam is divergent everywhere after the lens.

To achieve a minimal waist one needs a lens with a short as possible focal lenght. To achieve a maximal distance one needs a lens with a long as possible focal lenght. You can't have both at the same time.

@ Thread starter: What is your goal?

Singlemode
Click to expand...

I think you misunderstood Alaska's question. His question was: What focal length lens would be needed to focus a beam at a mile distance? Not about beam waist. Theoretically, a beam waist could for practical consideration be at infinity if a beam was expanded greatly then collimate with an extremely long focal length length lens.

The part in bold should be directly posted to the OP. If not he may not see it.
 
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R

Rintec

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Re: Beam expander to focus laser bearm

Alaskan said:
We need an optics guru for this one, I'm not at all sure how to focus a beam to a small spot at a great distance, I can use a normal beam expander which is adjustable to focus to a spot 30 feet out to burn nice holes in plastic, if using enough power, but I don't know if it is possible to focus a beam to a tiny converging spot a mile away, for example. How far away do you want to focus the spot?
Click to expand...

Let' say 50 m away.

Correct me if i m wrong.
Illustration:
I have a source of 1 watt laser with 5mm dia beam.
I want to make a spot of 2.5 mm dia 50 m away.
I can setup an expander (reducer) so that the output beam is a collimate one with 2.5mm dia.
Expecting very small divergence, the spot will be 2.5 mm something at 50 meters away.
But this is not what I want.

I want the beam has tiniest spot thus maximum power only at 50 m away point. Before and after it, it has less power.

Is this possible with expander or something like that?
Perhaps at first make the beam very large than converge it using the magic of concave lens....

Singlemode Laser said:
First, it is not possible to put the waist at infinity. For a given beam diameter and focal length of a lens, there is a maximum distance for the waist and after this the beam is divergent everywhere after the lens.

To achieve a minimal waist one needs a lens with a short as possible focal lenght. To achieve a maximal distance one needs a lens with a long as possible focal lenght. You can't have both at the same time.

@ Thread starter: What is your goal?

Singlemode
Click to expand...

Sorry if my question was not clear.
What I meant focus at infinity is the size of collimating beam (plus very small divergence).
So the term of waist may be wrong.
I hope what i explained above made my goal is clear.
 
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