Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Laser Genetics Genisys ND3 (Large Pics)

By flatter he means closer to parallel (0 mrad divergence) but not actually parallel since 0 divergence is impossible. Divergence is inversely proportional to initial beam diameter, so the wider the beam diameter at the aperture, the lower the divergence can be with good optics. Divergence is also a function of cavity length, which is why lasers with longer cavities have lower divergence than those with short cavities. Working with laser diodes is different than most other kinds of lasers. With a HeNe laser, the cavity is at least several inches long, which gives a nicely collimated beam with no collimating lenses at all. Diodes have cavities <1mm long which means their uncorrected output (no lens) is highly divergent. By placing a collimating lens a few mm away from the diode allows this highly divergent beam to expand a bit before being collimated, which means that diodes can be collimated to extremely low divergence numbers using just a collimating assembly. Here's a couple diagrams I made awhile back that help illustrate these concepts:

this diagram shows how a beam expander influences divergence in the far-field:

485-beam-expander-diagram.bmp


You can see how the spot in the far field is smaller than it would be without the expander, and overall divergence is less but not eliminated.

this illustrates the effect cavity length has on uncorrected divergence:

487-cavity-length-comparison.bmp
 
Last edited:





yuck Heath. That thing was Dirty. I good cleaning and that thing would have jump
up to 1W. :)
 
OK makes sense, but then it really doesn't matter if you use a beam expander because the beam will have better divergence, but still be the same width as a non-expanded beam, right? If so who even cares, a better divergence only matters on paper because the end dot will be the same.

will
 
Not quite. The far-field spot without a beam expander will always be larger than with a beam expander. The purpose of the expander is to lower the divergence over a greater distance.

For example, let's say you want to project a spot onto a mountain 5km away, and you want that spot to be 6m wide. You get out your laser pointer and project the spot, but you find that the spot is 10m wide at that distance. The only way to get that smaller spot is to use a beam expander to reduce the overall divergence, so that the distant spot meets the 6m diameter requirement.
 
Last edited:
Wow...I have learned a lot on this thread. :) I am happy that I made the review for this laser...LOL

Thanks for all of the information guys. :)
 
ossumguywill said:
OK makes sense, but then it really doesn't matter if you use a beam expander because the beam will have better divergence, but still be the same width as a non-expanded beam, right? If so who even cares, a better divergence only matters on paper because the end dot will be the same.

will
Click to expand...

What ElecktroFreak said in response shows clearly one application. But now review what you've said above. If that were true there'd be no reason for beam expanders. Since there are beam expanders in existence then what you've reasoned out can't be true. Do you see ?

It's a very simple concept. Expand the beam with one lens and collimate it with another lens will create a wider beam beam with lower divergence compared with a beam that comes from a diode without optics.
 
I have a non-solved question.
I use beam expanders like the ones I see in this thread in laboratory and they have at the bottom something that I think is called "rotatory barrel", or "rotatory adjustment". Moving this anything doesn't happen, but I think it change the diameter of the spot. This can be seen in a long distance I think, beacause I can't see any differcence in short distance moving it.
But if I change the size of the spot the beam can't be collimated anymore, except for a specific position .
So, is what I think right and what the adjustment is made for?
 
I am not sure as to what it is that you are talking about. I recomend that you start a new thread and introduce yourself to the community and then ask this question. It will also help if you post pictures of the divice that you are working with.
 
I am absolutely amazed at how many people have viewed this review. I think most of the people are finding it through my youtube video...but still, I am Baffled!!

This makes me happy and I feel as if it was worth my time making it. :)
Thanks,
Iskor12
 
iskor12 said:
This is how I picture it....Please keep in mind that I may very well be wrong.
Please, if I am wrong, let me and other people know. Thanks.

Laser on the left is (Normal) Laser on the right has a beam expander and is focused to have a small dot at 300ft
Capture-6.jpg
Click to expand...

I think you're wrong in the right graph. ;)The beam expander might make it have a big beam dia. at the aperture with lowest divergence. It's the default state but once you defocus the laser, the divergence enlarges also as the beam dia/ certainly will enlarge.

Due to its bigger-than-usual beam dia. at aperture, It will not be able to focus to a point for burning or so in spite of its low divergence.

Sorry i'm not good at drawing any graph. Hope i made myself clear.

mrsilva said:
In case anyone's interested, Dragon sell an adjustable $85 Beam Expander compatible with Viper, Aurora and Spartan series.

CNI also offer Beam Expander for their lasers.
Click to expand...

The beam expanders you cited are not adjustable. They are of fixed magnification. 2x or 5x or 10x. :)
 
Last edited:
> The beam expanders you cited are not adjustable. They are of fixed magnification. 2x or 5x or 10x.

The Dragon Beam Expander seemed to have an adjustable focus on the Youtube video, I'm not sure if its just the focus or if the divergence is also variable.
 
mrsilva said:
> The beam expanders you cited are not adjustable. They are of fixed magnification. 2x or 5x or 10x.

The Dragon Beam Expander seemed to have an adjustable focus on the Youtube video, I'm not sure if its just the focus or if the divergence is also variable.
Click to expand...

Yes, the lasers you saw are probably focus adjustable but not the beam expander. I had a 2x one in my collection.

Thorlabs provides a lot of variable beam expanders like this: Thorlabs.com - Variable Beam Expanders: Beam Expansion or Reduction . I trust their quality but the pricing of $1,875.00 is way too high. :gun:
 
As Dragon Lasers doesn't currently offer a beam expander for the Spartan 1W, I bought a CNI PGL-III-C-447-1W with 10x beam expander.

Dragon Lasers told me their beam expander is too narrow for the Spartan's 3mm beam. They are developing a new one which will be available in a few months.
 
You must log in or register to reply here.


Back
Top