Core's divergence?

[steve001]

Laserrod, I always thought this was what a collimator did:

LASER beam>====(]==[)---------TARGET

Doesn't that seem more logical? Wouldn't you want the beam to be more concentrated for burning?[/qoute]

In your diagram the beam would collimate with the first lens and spread with the second one.

To Gazoo
No and yes. the first lens will obviously focus the beam after which the beam will begin to spread. As it passes throught the second lens the beam can be made too focus or diverge or make the beam diverge optimally
This type of collimator using two positive focal length lenses is known as a Keplerian beam expander. If the distance between the lenses is the sum of the focal lengths then the beam is collimated optimally meaning minimal divergence.

 

[steve001]

Laserrod, I always thought this was what a collimator did:

LASER beam>====(]==[)---------TARGET


Doesn't that seem more logical? Wouldn't you want the beam to be more concentrated for burning?

Read my reply to Gazoo

This is what this type of expander does. The resulting beam will be larger at the aperture. Actually this is what all beam expanders can do

Laser<<<<<<(]>>><<<<<[)=====

 

[Angdvl089]

Laserrod that helped me a ton. So basically your taking a smaller beam with a positive divergence and making a bigger beam with negative divergence?

 

[RA_pierce]

My collimator i made works like this:
[LASER]---[)><[(----------
The first lens is plano-convex so it has a focal point at about 4.5cm.
The second lens is plano-concave and collimates the beam.
(All the diagrams I've seen on here use two plano-convex lenses and that would just make the laser into a flashlight.)
The two lenses in my collimator ate set at the best distance for collimation and the second lens can be adjusted to expand the beam or be removed, so the first lens can be used for focused burning. It works like a 'phony disruptor'- just waaaaay cheaper and isn't used for flash blinding people or stopping cars on a freeway.
Without the collimator my laser has a divergence of about .7mrad. I used the laserglow method to measure it.

 

[Gazoo]

[quote author=Angdvl089 link=1190270166/0#8 date=1190437099]
Laserrod, I always thought this was what a collimator did:

LASER beam>====(]==[)---------TARGET


Doesn't that seem more logical? Wouldn't you want the beam to be more concentrated for burning?

Read my reply to Gazoo

This is what this type of expander does. The resulting beam will be larger at the aperture.

Laser<<<<<<(]>>><<<<<[)=====[/quote]


Thanks for that and I understand...a larger beam sounds interesting. I might have to give it a go sometime.

 

[steve001]

My collimator i made works like this:
[LASER]---[)><[(----------
The first lens is plano-convex so it has a focal point at about 4.5cm.
The second lens is plano-concave and collimates the beam.
(All the diagrams I've seen on here use two plano-convex lenses and that would just make the laser into a flashlight.)
The two lenses in my collimator ate set at the best distance for collimation and the second lens can be adjusted to expand the beam or be removed, so the first lens can be used for focused burning. It works like a 'phony disruptor'- just waaaaay cheaper and isn't used for flash blinding people or stopping cars on a freeway.
Without the collimator my laser has a divergence of about .7mrad. I used the laserglow method to measure it.

You've your lens setup backwards Did you know that ?

 

[Rasel]

.. couldn't it work either way? I mean the first way you diverge the laser then you make it converge again. The second way, you converge the laser and then make it diverge. The second way would be better because you get a smaller beam diameter in the end.

:-?

 

[Thories]

HAHAHA this is almost the last question of my physics paper. member if it travels through the focal point it comes out parallel. so one lens focusing towards the other lenses focal point should cause it to travel out parallel from lens 2. now if u had really tiny lenses with tiny focal points you could minimize the spread that occurs between the two lenses thus getting a fine parallel beam. not sure what types of lenses ud need to use without doing an annoying ray diagram (i hate those things) but if u used bi concave/convex at the right focal points and distance surely it would work?

 

[likewhat]

Hey, I also posted this on spectraforum

I hope these pictures will make beam expanders make a little more sense to some people. (if someone could get the to post on here that would be nice)

imagehosting.com/show.php/1170171_beamresizing.bmp.html

If you start with a collimated beam that has a diameter of d and go through the lenses you get a resized beam that will have a diameter of d*f2/f1.

But what if your beam was not collimated when it entered?
You can adjust the spacing between the lenses, and at some point the output of it will be collimated. In fact, if you had two lenses that were of the same focal length and your incoming beam was just slightly not collimated, there would be some spacing (close to the sum of the focal lengths) that would give you a collimated beam.

Hope this helps someone.

 

[RA_pierce]

[quote author=RA_pierce link=1190270166/15#19 date=1190492185]My collimator i made works like this:
[LASER]---[)><[(----------
The first lens is plano-convex so it has a focal point at about 4.5cm.
The second lens is plano-concave and collimates the beam.
(All the diagrams I've seen on here use two plano-convex lenses and that would just make the laser into a flashlight.)
The two lenses in my collimator ate set at the best distance for collimation and the second lens can be adjusted to expand the beam or be removed, so the first lens can be used for focused burning. It works like a 'phony disruptor'- just waaaaay cheaper and isn't used for flash blinding people or stopping cars on a freeway.
Without the collimator my laser has a divergence of about .7mrad. I used the laserglow method to measure it.

You've your lens setup backwards Did you know that ?[/quote]

Yup. And it works perfectly fine.

 

[Aseras]

the point of collimination is to uses lenses to bend the light straight. If you light is expanding ( normally ) your first lense will converge it and you align the second lense to negate it and keep the light as parallel to emission as possible. You can also do the reverse but it's very hard. Upcollimation is easy. down collimintaion is possible but expensive and very hard to do since oyu need tiny lenses that aren't lossy and can handle HUGE power desnities.

so you are going [ch1776]<=[ch8801])=[ch8801]–-(=========

 

[RA_pierce]

Yeah the diameter is slightly larger but the divergence is at less than .3mRad.

 

[Things]

hmmmm i took a pic of the aperature for some reason.

 

[steve001]

[quote author=steve001 link=1190270166/15#21 date=1190497359][quote author=RA_pierce link=1190270166/15#19 date=1190492185]My collimator i made works like this:
[LASER]---[)><[(----------
The first lens is plano-convex so it has a focal point at about 4.5cm.
The second lens is plano-concave and collimates the beam.
(All the diagrams I've seen on here use two plano-convex lenses and that would just make the laser into a flashlight.)
The two lenses in my collimator ate set at the best distance for collimation and the second lens can be adjusted to expand the beam or be removed, so the first lens can be used for focused burning. It works like a 'phony disruptor'- just waaaaay cheaper and isn't used for flash blinding people or stopping cars on a freeway.
Without the collimator my laser has a divergence of about .7mrad. I used the laserglow method to measure it.

You've your lens setup backwards Did you know that ?[/quote]

Yup. And it works perfectly fine.
[/quote]


Sorry your wrong. You will not be able to collimate a laser beam over any significant distance if the last lens the beam travels through is a negative focal lens. Lenses that have a negative focal length will diverge light. This applet will show you precisely what I mean http://www.lightmachinery.com/gausbeam.php
This applet works best with Internet Explorer

Focal lengths of the lenses can be any length.
First lens separation should be 1mm
First lens focal length 6mm
Second lens separation start with 48mm
second lens focal length - 48mm

now start decreasing the distance of the second lens and watch how the rayleigh range changes. Do you notice that this range is less than 1mm and that it has increased just a bit from its original distance.

now repeat this procedure again, but this time the 6mm lens will have a negative focal length and the 48 mm lens a positive focal length. Start the second lens at 48 mm distance. Then start to decrease the distance. Watch how the Rayleigh range increases dramatically. There will be a point where the beam is optimally collimated.

 

[Orr3]

When I measured my Core I also got .3 mRad.

 

[BooBoo]

Its amazing that anyone would put Any Stock in the claims almost any laser manufacturer make about thier products divergange....Especially WickedLasers and any of thier lasers, including the Core.
As None, I have ever bought, (even counting a small few of my laser, not bought from WickedLasers), were ever Delivered within Specs of such.....and with the experiences of most long time laser-Enthusiasts....many here ought to already know that, you get what you get, and then try and tweak the focus, and such, to get the divergance you wish... or RMA RMA RMA, and pay enough in shipping, to where you could have bought another one or two lasers with....Before getting one that is as advertised and within specs.