Beam Expanders !

[Accutronitis]

Can someone please explain the pros and cons between a 3x and 10x beam expander and what does a zoom able beam expander give you ?

 

[diachi]

Can someone please explain the pros and cons between a 3x and 10x beam expander and what does a zoom able beam expander give you ?

3X:
Pro: Expands beam by 3x, reduces divergence by 3x.
Con: Doesn't reduce divergence as much as a 10x.

10x:
Pro: Expands beam by 10x, reduces divergence by 10x.
Con: 3.3333...x fatter beam in the near field compared with a 3x. Likely physically bigger.

Zoomable = adjustable focus.

There's other things to take into account, not just expansion factor. Those things will vary based on which specific expander you use.

 

[Alaskan]

Expanders also reduce power out and the beam isn't as bright due to the power being spread out over a larger area. Regardless, has never bothered me, I prefer a lower divergence beam so I can see a spot on a cloud base 7,000 feet high. Many pointers won't do that because their divergence is too high and the power spreads out too much before it reaches the cloud. I've been able to see a spot on a cloud base as high as 12,000 feet with a 1 watt 532nm laser pointer expanded to 10X.

 

[Accutronitis]

3X:
Pro: Expands beam by 3x, reduces divergence by 3x.
Con: Doesn't reduce divergence as much as a 10x.

10x:
Pro: Expands beam by 10x, reduces divergence by 10x.
Con: 3.3333...x fatter beam in the near field compared with a 3x. Likely physically bigger.

Zoomable = adjustable focus.

There's other things to take into account, not just expansion factor. Those things will vary based on which specific expander you use.

Like what should be taken in account ?

I just bought a Jetlasers 10X Adjustable Beam Expander for PL-E Pro series with 1-10X magnification with adjustable focus to correct for laser beam divergence.

Doesn't 1-10X magnification you can change the beam expansion from as low as 1x to as high as 10x ?

Expanders also reduce power out and the beam isn't as bright due to the power being spread out over a larger area. Regardless, has never bothered me, I prefer a lower divergence beam so I can see a spot on a cloud base 7,000 feet high. Many pointers won't do that because their divergence is too high and the power spreads out too much before it reaches the cloud. I've been able to see a spot on a cloud base as high as 12,000 feet with a 1 watt 532nm laser pointer expanded to 10X.

I get the part where the beam is expanded and over all the power is reduced but after refocusing the beam back to a point at lets say 5000 feet doesn't that bring the power back up at least some in that point at 5000 feet ?

 

[Alaskan]

I have one of those and I never set it to 1X, didn't even realize it was advertised for 1-10X, always had it on maximum expansion. I don't know how it could really do 1x, that would mean the input beam is the same diameter as its output, no change. Is that even possible? If they advertise it as such, it must be, I didn't realize I could adjust it through that wide of a range. Theoretically, at 1X you will have no expansion and your divergence the same, but less power due to losses. However, the loss shouldn't be very much with that expander, nicely AR coated.

Edit: A beam expander, if adjustable, can be focused to a point to bring the power back into a smaller area, but the range of focus doesn't allow you to do that for long distances that I've ever seen. Unless you want to burn something a few feet away, they are normally focused to infinity, just like a regular laser collimator lens is focused to infinity so the light is as parallel as possible without a focal point, just goes on forever as parallel light without being focused to a point, except for the divergence, which causes it to spread. If a laser pointer has 1 mRad of full beam width divergence, every meter the beam travels it will expand by 1 millimeter wider. Put a 10X expander on a laser pointer which has 1 mRad of divergence, the beam will spread .1, or one tenth of a meter every meter it travels forward.

If someone can tell me how large a lens needs to be to focus the light to a point 5000 feet away, I'd really like to know, I have been wondering this for a long time now. The divergence would need to be uber low to do that, and thus a very big lens. I don't know if such is even possible.

 

[Accutronitis]

I have one of those and I never set it to 1X, didn't even realize it was advertised for 1-10X, always had it on maximum expansion. I don't know how it could really do 1x, that would mean the input beam is the same diameter as its output, no change. Is that even possible? If they advertise it as such, it must be, I didn't realize I could adjust it through that wide of a range. Theoretically, at 1X you will have no expansion and your divergence the same, but less power due to losses. However, the loss shouldn't be very much with that expander, nicely AR coated.

Edit: A beam expander, if adjustable, can be focused to a point to bring the power back into a smaller area, but the range of focus doesn't allow you to do that for long distances that I've ever seen. Unless you want to burn something a few feet away, they are normally focused to infinity, just like a regular laser collimator lens is focused to infinity so the light is as parallel as possible without a focal point, just goes on forever as parallel light without being focused to a point, except for the divergence, which causes it to spread. If a laser pointer has 1 mRad of full beam width divergence, every meter the beam travels it will expand by 1 millimeter wider.

1x lol ya I didn't even think of that, Times one is just the same as it was to start with ! lol

I've read about members burning things from across the back yard using a beam expander, For sure I've read people saying they were burning up stuff from across the room using a beam expander ? But for sure they were TALKING about much further than a few feet, Were they using a BE with more than 10x ?

 

[Alaskan]

I edited my first post, as usual.... I shouldn't post until done editing. I've burned stuff 15 feet away by using a 3 inch diameter PCX lens that I had on a pointer as an expander, when focused down to a point that far away, but I could never get it to focus to a point 50 feet away.

Edit: See this for one of my NUBM44 projects:

http://laserpointerforums.com/f49/lazy-mans-beam-expander-445nm-nubm44-6-watt-laser-diode-94802.html

 

[Accutronitis]

I've seen a few BE on ebay that were huge and selling for something like $5,000.00 !

 

[Alaskan]

I saw one like that too, but it was AR coated for a very long IR wavelength which I cannot use, and over priced for ebay, I thought. I have purchased two 6 inch diameter Special Optics beam expanders on ebay, one for 20X the other for 160X. The 160X cannot accept a beam width of more than about 1mm.

Here's another thread I made about using a telephoto camera lens as a collimator, allowing the beam to spread that wide from the diode and then collimating it is doing the same thing. Doesn't matter if you just collimate your beam with a longer focal length larger diameter lens, or using a beam expander which can take the output of an already collimated laser beam and then expand it and focus back to infinity, either way the beam is being expanded further and will produce proportionally less divergence.

http://laserpointerforums.com/f49/m...photo-lens-converted-beam-expander-95082.html

 

[Accutronitis]

YES ! I had seen that and right after I got done reading that I started digging around the house to find my dads really nice telephoto camera lens but once I found it I had no idea what to do with it ! LOL

I know this is a good one (not that you can tell that from these crappy pictures) but I don't have a clue if it could be used for anything ? It sure has plenty of great looking glass in it !

 

[Alaskan]

That might be something you can use, but I'd look for a 500mm telephoto lens on ebay, they can sometimes be found for twenty dollars. Only thing is, some of them have two lenses, one in the base and one on the end. If I find that, I like to remove the first lens and just leave the one in the end, or the objective lens in. Depending upon it's focal length this could cause a problem because the tube then might not be the correct length for mounting on your pointer with some kind of diameter adapter. I don't want that first lens in the tube because it adds loss and wasn't the correct focal length to use with a pointer anyway, not the one I had.

The longer focal length of a 500mm telephoto lens is better for use as an expander. Also, I have found if the beam is expanded to no more than 1/2 the diameter of the collimating lens, the splash won't show very much, if at all. In my experience those wings will appear if you fill up the entire objective lens using the NUBM44.

IIRC the 500mm telephoto lens I used had a 70mm diameter objective lens. I don't know if this same benefit of eliminating the wings would happen for smaller diameter objective lenses with the NUBM44 laser diode.

To get one of those to work as a beam expander, what I do is leave the G2 lens (or what ever lens you are using) in the pointer, and then defocus it so that only half the diameter of the objective lens in the telephoto unit is filled with beam, then adjust the telephoto lens to collimate the beam to infinity. It takes some juggling between the G2 focus, the distance the telephoto object lens is from it, but once things are set up right, I was able to get a fully collimated expanded beam without wings and use the telephoto lenses focus ring to adjust to infinity, or to focus close in to burn things.

BTW: What happened to your hands? No longer old dude hands like mine. Maybe just the angle or other photo made them look different, or you had your dad holding the parts when taking those photos?

 

[Accutronitis]

That might be something you can use, but I'd look for a 500mm telephoto lens on ebay, they can sometimes be found for twenty dollars. Only thing is, some of them have two lenses, one in the base and one on the end. If I find that, I like to remove the first lens and just leave the one in the end, or the objective lens in. Depending upon it's focal length this could cause a problem because the tube then might not be the correct length for mounting on your pointer with some kind of diameter adapter. I don't want that first lens in the tube because it adds loss and wasn't the correct focal length to use with a pointer anyway, not the one I had.

The longer focal length is better for use as an expander. Also, I have found if the beam is expanded to no more than 1/2 the diameter of the collimating lens, the splash won't show very much, if at all. In my experience those wings will appear if you fill up the entire objective lens using the NUBM44.

IIRC the 500mm telephoto lens I used had a 70mm diameter objective lens. I don't know if this same benefit would happen for smaller diameter lenses with the NUBM44 laser diode.

To get one of those to work as a beam expander, what I do is leave the G2 lens (or what ever lens you are using) in the pointer, and then defocus it so that only half the diameter of the objective lens in the telephoto unit is filled with beam, then adjust the telephoto lens to collimate the beam to infinity. It takes some juggling between the G2 focus, the distance the telephoto object lens is from it, but once things are set up right, I was able to get a fully collimated expanded beam without wings and use the telephoto lenses focus ring to adjust to infinity, or to focus close in to burn things.

oh I see mine is just a 200mm, I was just trying to see if I could make something very cool out of something that was just collecting dust and do so with no money or at least very little money, You know what I mean ?

 

[Alaskan]

You could probably make it work, one way or another.

 

[diachi]

oh I see mine is just a 200mm, I was just trying to see if I could make something very cool out of something that was just collecting dust and do so with no money or at least very little money, You know what I mean ?

Experimenting can be a big part of this hobby, it can be interesting messing around with different optics you have lying around. Especially if you're someone that learns by hands on experience. :beer:

 

[Accutronitis]

Experimenting can be a big part of this hobby, it can be interesting messing around with different optics you have lying around. Especially if you're someone that learns by hands on experience. :beer:

I'll get back to you on that if I get some extra time because right now I don't think the "effort" to "reward" ratio is high enough for that project right at this moment..... lol

 

[Radim]

I think there was almost everything important said in general. I just add there are many types of expanders. Considering refractive expander types there are two basic types - Keplerian and Galilean expander. They basicaly differ by real and virtual focus points, where real focus point in Keplerian might be a problem in high powered laser uses due to extreme energy densities at that point degrading wavefronts of laser beam - effects caused by air heating.

Nice explanation into beam expanders optics is here.