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Interested in Beam Expanders ???






Pman

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This would be a really great project. Encouragement all the way!
I own a 2x I purchased from Isaac but admittedly there's multiple adjustments so I'm not actually sure how to use it properly. If someone has a clear simple explanation on how to use it properly I would appreciate it very much. It did come with the adapters for more than just my Spartan. Think it would be easier if it was at least 5x.
 
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Yes, two lenses, an expander and a collimation lens for one type, the most common type as below, consisting of a biconcave and a plano convex lens:

BeamExpander_zps1ba6334c.jpg


The above photo ripped from this document: http://assets.newport.com/webDocuments-EN/images/How_to_Build_a_Beam_Expander_5.pdf

To me, the above drawing is a bit misleading because the beam should be expanded enough to cover 80 percent or more of the output lens diameter, to do that, the right expander lens would need to be selected with a shorter negative focal length, the shorter the negative FL the wider the expansion. The following diagram shows the virtual focal length of a negative biconcave lens:

You need to take care of the wavefront of the beam too. For a singlet lenses that means big f numbers or long a focal length and a small diameter.

Probably a Keplerian style is more affordable as two focusing lenses easy to get than one defocusing (negative) + focusing as in Galilean.

I think that the first picture should have a focusing lens reversed, i.e., a convex is out.

Some theoretical reading in Google books
Lens Design, Third Edition, - Milton Laikin - Google Books
 
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Thanks, I don't understand wavefront, some reading is due, thanks for the link. I was wondering if the PCX lens was backwards myself.
 
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Keplerian works fine at lower powers, but
at high powers the air begins to heat up at
the focal point and cause distortions.
That is why all modern commercial beam
expanders are Galillean. The space ahead
of the focal point is also eliminated
making for a shorter length overall.
 
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I compared the Newport example (CXP) and a reversed lens (PCX) setup. PCX has 4x less spherical aberrations.

Thanks, PCX it is for me then. I have a huge 12 inch diameter lens I'd like to turn into a beam expander if I can get the right tube and concave lens for it's 34 inch FL. Anyone know how to determine the neg FL expander lens I need? This lens is not completely flat on one side, it has a small amount of curve on the flatter side, maybe it won't work with that.

Untitledtt_zpsc97912b8.jpg


eHow to build a laser beam expander: http://www.ehow.co.uk/how_7880935_build-laser-beam-expander.html
 
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Well, it really depends on the diameter of
your input beam. Assuming a max of about
5mm, 60X would be a safe magnification.
That would require a 14mm FL lens set back
877.6mm from the objective.
 
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Thank you for your input, do you mean negative 14mm FL?

With my cheapo 50-100mw China lasers, I can remove the collimation lens and with its output expanding without collimation, I can place the laser far enough away from the big 12 inch lens so that it expands to 80 percent the diameter of that lens, then it should work fine and become a beam expander that way, right?

If true, we don't need to do the math or find the perfectly matched expander lens, just place your laser far enough back (with its collimation lens removed) until the beam covers 80 percent of your larger PCX lens and you are done. Or, find just about any old concave lens which can expand your laser beam without removing your lasers collimation lens and then pull back both your laser and that concave lens away from the larger PCX lens until the light covers 80 percent the diameter, done! Right?
 
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I wish it worked that way. If the
expanding lens is too strong, the incoming
angle will be so great that the lens will
be unable to bend it straight. If the
incoming beam is too wide, then as you get
back far enough it will be wider than the
objective. Then there is the opposite
problem when it doesn't expand enough and
you get a wimpy little beam coming out.
 
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I already did this using a laser pointer without a collimation lens together with a telescope without an eye piece and it worked, I just had laser far enough away from the objective lens so that the spot was big enough to cover close to 80 percent of the lens and it worked, but I did have to use the telescopes focus adjustment (in and out slider) to tune it to the low divergence sweet spot otherwise known as infinity.

I was able to do this using just one lens instead of the four used in a normal laser and expander coupling due to the following:

After removing my el cheapo 70mw 532nm lasers internal expander lens as well as its output or collimation lens (which together are an internal expander, something all of the 532nm lasers I've seen have) the beam spread out fairly fast directly out of the crystal, but not as fast as it does if I left the expander lens on the crystal (for some telescopes, you might need to leave that expander lens on, depending on the characteristics of the laser and the length of the tube). Without any other lenses between the internal crystal and the output, I then coupled the laser to a 900mm long telescope (without an eye piece lens). The telescopes tube was just long enough to allow the lasers beam to expand enough in size to cover most of the 60mm objective lens, because of this I did not need the eye piece or an expander lens. The laser was just small enough to fit inside the tube where the eye piece would have been and when I took it outside and pointed it into the night sky, it produced a lovely low divergence fat beam on the output.

Below, photo of the lenses found inside my cheap 70mw laser pointer; collimation lens, expander lens and crystal assembly. Every DPSS pumped 532nm laser I've seen has a mini-beam expander built into it to reduce the divergence, these lenses are made from cheap plastic.

02b23fbb-3443-4158-9f0f-02e011ebf263_zps84ae2944.jpg


From this, I believe I reduced the divergence the same as if I had used a beam expander, but without the loss of an expander lens in the laser itself, the lasers collimation lens as well as without the additional expander lens on the input of a normal expander (or eye piece of a telescope), this reduced the number of lenses by three, only needing one. From all of this, I really didn't have a beam expander at all, I just let the lasers beam expand to close to 50mm before collimation with a 60mm lens to reduce the divergence that way, but I had to use a long tube to do it.

The Lightning Stalker:
I'd like to understand you regarding the possibility of the expanding laser light being at too high of an angle for the lens to be able to collimate the light properly. I can understand the glass can only bend the light so much for a given thickness, is that the limiting factor and because of this, there is a maximum angle which can be used with any given lens ?

If he doesn't answer, could someone please help explain this to me, can I really have too high of an angle from a concave lens for a PCX lens to be able to collimate the energy?

I've spent about an hour trying to write this post so it could be easily understood, damn! Here's a picture of another telescope I found for three bucks at a thrift store where I did the same thing, but with this pointer, I left it's expander lens glued onto the crystal holder, just removing the collimation lens and the beam expanded enough to cover most of the objective lens making a nice little beam expander, compared to the 900mm FL one I have. The opening where the eye piece would have been was just large enough to allow me to insert the head of my 70mw laser pointer into the tube (eight dollar laser on ebay, search 8000m 532nm).

8fa9aab2-df0d-4ef4-864f-2b40642f8179_zpsf565a68f.jpg
c4d85509-13dc-43bb-a9dc-c9e11c348a38_zpsb6acdba0.jpg


Below is a photo of the 900mm FL telescope I wrote about above, in this photo I have my 175mw LaserGlow pointer taped to it without an eye piece but I do have two expander lenses in series between it and the telescope. There is no way I would modify my nice Aries pointer! The photo of the lens next to it is a concave lens I bought on ebay cheap, used two of them to get the laser beam to expand enough.

dfdde58b-4a98-4e24-9283-ebc08bd20187_zps576b0562.jpg
9dd8f61b-e9dc-4d66-b3a8-9103ff45ccf4_zpsba6f379b.jpg


Here's a photo of the 900mm FL telescope showing its fat beam outside at night during a light drizzle, the green spot you see at the end of the beam is the base of a cloud the beam was hitting.

DarkNightExpanded_zps4f4573f9.jpg
 
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The Lightning Stalker:[/U] I'd like to understand you regarding the possibility of the expanding laser light being at too high of an angle for the lens to be able to collimate the light properly. I can understand the glass can only bend the light so much for a given thickness, is that the limiting factor and because of this, there is a maximum angle which can be used with any given lens ?

Yes, that is correct.
 
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THANKS. As always you are helpful. I will have to start experimenting with a PCX lens and a pointer to learn more.
 
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THANKS. As always you are helpful. I will have to start experimenting with a PCX lens and a pointer to learn more.

Here's an easy way with this app.
gausian beam rev 2.0.xls

I don't own a Mac and have not used this one
Simple beam propagation calculations using a Mac pc.
ABCD - Laser Beam Propagation software for Mac OS X

Here's a result using your 34fl length lens and a -6fl lens and assuming your laser has
Beam size 1 mm
Divergence 1.5 mrad

Surface = the diode
Separation length = distance from the diode. I chose 5 mm
Focal length = the focal lengths of the lenses I choose -6mm fl and 34inches fl (863.6mm)
Divergence is self explanatory in this case = 0.01mrad per meter after the Rayleigh length (range)
Rayleigh length = the beam's spread which is 1.4 times the initial beam diameter
when the beam is optimally collimated for lowest divergence = 13432516.440mm in miles = 8.348363 miles. Beyond that length the beams expands just like a flashlight beam does.
Diameter = the beam diameter at the collimating lens = 143.954mm = 5.66748 inches.
To figure the correct spacing between the two lenses input the focal length on the 34 inch fl lens into the second box line and the reduce the spacing between the lenses. Start at 863.6mm
I hope this is clear. If you need more help let me know.
 
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