Dragon Laser Beam Expander

[steve001]

My local surplus shoppe has a half dozen or so adjustable beam expanders. The scales are labeled 2-10x and they're coated for 1064nm. They're only $20 per so I'm interested enough that I plan on picking up 1 or 2 the next time I go there for some other bits-n-pieces but I was wondering if anyone here would know if the the 1064 coatings would work reasonably well for 532nm or whether I'd be wasting half of my photons. (PM me if you'd like me to snag one for you) Thanks!

Most of your photons would be lost. You can get an idea I think how much light would be lost by visiting http://www.edmundoptics.com/

 

[steve001]

Added edit: If you do buy another beam expander, the input must be wider than your expanded beam to use it in series from another one, of course.

You don't do it in series. All you have to do is use a longer focal length lens. You to create a shorter focal length *expansion lens stack two negative or more lenses together. The lens also has to be wider so you capture all of the beam. If you don't understand then look up Galilean beam expander. Think refractor telescopes.
There's a youTube video using a green laser and a refractor telescope focused at 300 feet popping a balloon.

* negative expansions lenses with a focal length shorter than -6mm are hard to come buy.

 

[Alaskan]

I understand the right way to do it, the right way to expand a laser beam with minimum loss, but I still think two beam expanders in series would work, as long as the beam from the first one wasn't too big to pass through the input lens of the second one, don't you agree? I'm looking for some good negative lenses now, bi-concave lenses. To produce a 40X expander for 808nm from a FAP unit, can you help out and give me some figures I can use to find the correct lenses? Do you know if 40X is possible for such?

Edit: Here's an EdmondOptics video on selecting beam expanders: http://www.youtube.com/watch?v=pjVb37f4GK4

 

[WizardG]

Most of your photons would be lost. You can get an idea I think how much light would be lost by visiting http://www.edmundoptics.com/

I checked out your link Steve and according to Edmund, losses for any of their standard coatings would be under 5% @ 532nm. I think you slipped a decimal place ;-)

But of course, that would be per surface. I'm gonna have to get a couple of those BEs and check out how many elements are in each one. I have access to a LPM @ work so I'll let that be the final judge.

 

[Alaskan]

RE: Galilean beam expander

I've looked for three days on the net and read articles, watched videos but they don't speak expanders for Newbie DUMMIES language well enough for me to be sure I understand. If someone would check me on this I'd sure appreciate the help:

It appears for a Galilean beam expander I can use my choice of negative lens on the input (double concave or what have you) as long as it can take the power and the diameter of the laser beam isn't too big for the physical size of the input lens. Of course, the expanded beam from the first lens should not be expanded so far that it overshoots the size of the next lens which re-collimates the laser beam into a wider but lower divergence output. Also, my understanding is you want a much longer focal point for the output or positive lens than the input negative expanding lens because the ratio of their individual focal lengths determines the expansion factor, when the first or negative lens has a relatively short focal length compared to the larger convex collimating output lens.

Do I have this right? To determine the expansion ratio or how much larger your collimated beam will be you only need to divide the focal length of the output lens by the focal length of the input lens and the resulting number is the expansion factor. (Again, only if the input beam isn't too big for the input lens or expanded too far for the amount of space the output lens has, i.e. overshooting its diameter, preferably staying at or below 90% of it's diameter as one individuals suggestion, if possible).

From what I've found searching around online on this subject, an inexpensive telescope will act as a beam expander too, if true that is probably the way to go if you want a large amount of expansion cheap (fleabay etc), as long as the input lens isn't too small for the diameter of your lasers beam and can take the power. For my own wants such won't do well for me because it doesn't appear there is a cheap way of doing what I need when I want to expand a 50W ~800nm laser by over a factor of 40, close to twice that if I can afford it or can find optics which will work to do so.

I found a convex lens with a 4000mm focal point, hummmm...... Maybe! (Yes, over 13 feet). I know, it will need to be mounted but I never said I was making a conventional laser pointer.

Edmund Optics video on beam expanders: Selecting the Right Beam Expander - YouTube

Link to Edmund Optics Beam Expander Application Notes: http://www.edmundoptics.com/technical-resources-center/lasers/beam-expanders/

 

[steve001]

I understand the right way to do it, the right way to expand a laser beam with minimum loss, but I still think two beam expanders in series would work, as long as the beam from the first one wasn't too big to pass through the input lens of the second one, don't you agree? I'm looking for some good negative lenses now, bi-concave lenses. To produce a 40X expander for 808nm from a FAP unit, can you help out and give me some figures I can use to find the correct lenses? Do you know if 40X is possible for such?

Edit: Here's an EdmondOptics video on selecting beam expanders: Selecting the Right Beam Expander - YouTube

Here's the rub. Introducing more optical elements will cause more loss in light transmitted. There is also the problem of aligning two beam expanders.

Theoretically there is no limit to decreasing beam divergence. There are practical reasons though.

For experimental purposes go to Anchoroptics.com. Then when you have everything worked out go to Edmund Optics. They carry the widest selection of off the shelf AR coated lens found anywhere in the world. Quality lenses cost money you know that, right?

Playing some educated guessing with some numbers you might get a spot size of 47.1mm [1.8 inches] at a range of 13.71miles

 

[Alaskan]

Thanks for the advice and practical info too, I've already spent thousands on this project between high current regulated variable voltage sources, laser power meters and the lasers themselves so I have no problem paying for quality lenses. I'm also considering the use of a spherical mirror too, found a nice 15 inch diameter optical quality one made in Germany with a hole in the middle, thinking that might be a way to go too but the focal point is another issue.

 

[steve001]

Thanks for the advice and practical info too, I've already spent thousands on this project between high current regulated variable voltage sources, laser power meters and the lasers themselves so I have no problem paying for quality lenses. I'm also considering the use of a spherical mirror too, found a nice 15 inch diameter optical quality one made in Germany with a hole in the middle, thinking that might be a way to go too but the focal point is another issue.

One other thing. A plano-convex lens is easier to mount.
I've heard of using mirrors, but I have not seen any for sale.
I forgot what wavelenght you will use. Which is it?

 

[Alaskan]

Steve,

I'm going to use 808nm. I'm looking at lenses with a flat side for either the input or output lens too, trying to see what it adds or takes away to have both sides the same or one side of a lens plano. I see designs for beam expanders with lenses either way for both the input and outputs glass. My guess is that having both sides concave or convex just makes the lens more refractive in either expansion or convergence for a given cut, would that assumption be correct? If true, then you could buy a lens with a plano side which can have much the same properties of a bi-convex or bi-concave, just requiring a deeper cut for the same amount of refraction for the same properties, up to a limit, I imagine. If my concepts are wrong someone please give me a heads up, still trying to get my bearings on basic optic principles.

I'm also trying to see if there is much advantage to using a spherical mirror as the collimating device in a beam expander and then having the resulting beam go through a convex refractor lens too, as a second collimating device, if that would give me a lower divergence than one alone. Of course, at a cost of additional loss when using both together. Doing google searches on that now, hard to find the answer.

Here are some ray patterns for spherical mirrors: https://www.google.com/search?q=sph...AWEnoCAAg&sqi=2&ved=0CCcQsAQ&biw=1188&bih=585

Edit: Here's a ray pattern of a convex-plano lens I just found, this answers some of my basic questions, the right most illustration shows how a diverging light from a negative lens is collimated into a parallel output. .

This ray pattern of a spherical mirror, below, shows how it can collimate diverging light into parallel beams. From this it appears the addition of a convex lens in front of the mirror will only collimate parallel light back into a focal point:

So, the idea of placing a convex lens in front of the output of a spherical mirror used to collimate diverging light into a parallel output won't work. Next is to find a way to use a large mirror and a lens alone to make a large beam expander, I don't know yet, still searching. My take on the situation right now is the mirror can be used in place of a convex lens but the focal point isn't very long for the spherical mirror I found, I need to find a shallow spherical mirror so that it has a long focal length to use as a beam expander with a negative lens. I'm hoping to find a light weight mirror with a long focal point instead of a lens to save weight and allow a tighter divergence over a refractive convex lens in its place.

 

[chaidy]

Remmy460
Dragonlasers got a new BE, Generation II. Go order one