Beam double expander

nikosb · Dec 15, 2014

I am working on a project where I want to expand the laser beam from a 10mW-30mW laser in a short distance. I attach a picture for illustration:

The idea is to use a first lens to expand the laser beam so that is attains a diameter of about 5cm in a short distance of about 5cm (angle of divergence around 30-45 degrees). Once the beam is expanded a second lens would be used to reduce the beam divergence to about 10 degrees. I have seen similar things using a double concave and a double convex lens, like an inverted Galilean system, but in those cases the laser beam after the second lens is collimated. In my case I would want to keep a beam divergence of about 10 degrees. Can that be done is a simple and inexpensive way like the inverted Galilean system?

Alaskan · Dec 16, 2014

You want a 10 degree wide beam? Maybe you can just have a variable focus lens and just do it that way, take it out of focus until the beam is 10 degrees wide.

Hemlock_Mike · Dec 16, 2014

That is a basic expander. A -FL input lens will shorten the device.
What lenses are you going to use -- What X magnification?
HMike

I usually start with a -10 mm PCC coated lens followed by a 50 mm PCX lens
for a 5X expander. Move the objective lens for beam size.

More: For my CO2 expanders, I use a -1" Diverging lens and 3, 5 or 7.5" objective
lenses (ZnSe) which give me between 3x and 7.5x power. Also, I get more room for
adjustment.

nikosb · Dec 16, 2014

I am learning about laser optics. I am not sure which lens would be suitable. The idea is to take the basic laser beam which is about 1.5mm in diameter, expand it to about 4-5cm within 4-5cm distance, and then use a film with an image and project the image ahead with a small expansion angle.

Hemlock_Mike · Dec 16, 2014

I usually draw this on graph paper so I can "see" the
beam. You may need a large objective lens for this.
I'll try to draw this out tomorrow so I can "see" it !!
HMike

lazeristasUVISIR · Dec 16, 2014

nikosb said:
I have seen similar things using a double concave and a double convex lens, like an inverted Galilean system, but in those cases the laser beam after the second lens is collimated. In my case I would want to keep a beam divergence of about 10 degrees. Can that be done is a simple and inexpensive way like the inverted Galilean system?

You do a Galilean telescope/expander, and then move a convex lens closer to the concave to get your desired divergence.

You have all parameters set: an initial beam 1.5 mm, final 50 mm, your wanted distance between lenses ~50 mm. Your homework is to calculated required focal lengths of lenses.

One thing to keep in mind: 1.5->50 = 33x magnification. That's a lot. A simple concave+convex might be not good enough.

Alaskan · Dec 17, 2014

I could use some help too, if I have 40mm dia. PCX with 300mm FL, what concave lens do I need which expands the beam to use 80% of the lens diameter, or 32mm? If I understand correctly, to make a 10X expander, I'd need a -32 mm FL concave lens?

When it comes to the diameter of a plano-convex expander lens on the input of an expander what should I have? Does it matter if the lens is two times, three, four or ten+ times the diameter of the collimated laser beam it is interfaced with?

I cannot seem to find what a PCC lens is.

Much appreciate advice too.

lazeristasUVISIR · Dec 17, 2014

Laser Project said:
I could use some help too, if I have 40mm dia. PCX with 300mm FL, what concave lens do I need which expands the beam to use 80% of the lens diameter, or 32mm? If I understand correctly, to make a 10X expander, I'd need a -32 mm FL concave lens?

You did not provided the initial beam size you want to expand.

Expander magnification: a ratio of the focal lengths of lenses. Thus for your M=10 and fcx 300 -> fcv = -30 mm.

There is another tutorial: http://www.edmundoptics.com/technical-resources-center/lasers/beam-expanders

Alaskan · Dec 17, 2014

Thanks, I was ignoring the width of the input beam, oops!

I don't know what a 1 watt 520nm laser diode will put out for a beam size using a G2 lens, I'm guessing 2mm. If the beam is 2mm wide (someone please correct me if too small), at 10X then the spot uses the entire diameter of the 40mm output lens, is that something I shouldn't do, use the entire width of the output lens? I read in a beam expander article not to do that but not the reason why.

lazeristasUVISIR · Dec 19, 2014

Laser Project said:
Thanks, I was ignoring the width of the input beam, oops!

I don't know what a 1 watt 520nm laser diode will put out for a beam size using a G2 lens, I'm guessing 2mm. If the beam is 2mm wide (someone please correct me if too small), at 10X then the spot uses the entire diameter of the 40mm output lens, is that something I shouldn't do, use the entire width of the output lens? I read in a beam expander article not to do that but not the reason why.

From G2 lens specs found on internet: EFL 4 mm, CA 5.3, NA = 0.6 and a divergences for 520 nm 1 W, I expect a ~5 mm beam on a longer axis. Maybe someone has an actual laser and measured it.

For your 40 mm lens a magnification can be smaller than 10x -> ~7x. With CX f= 300 mm -> CV ~40-50 mm.

To overfill your big lens is not good: you'll loose power on clipping and create diffraction rings. This might be not a big deal as a beam of 1 W is not a perfect anyway :thinking:

Alaskan · Dec 19, 2014

Thanks, my internet searches were not fruitful, looking in the wrong places, chasing the wrong links or asking the wrong questions. OK, I have some round beam correcting optics which will take care of a large amount of the long axis, at a cost for loss, of course. It appears when I ask the people selling 520nm laser diodes they do not want to answer the question directly, giving answers such as "about the same as a M140 diode" or, "I will have to test to see" and then no answer. My take on this is they don't want people to know how wide the beams are, prefer selling more of them without being quoted!

Thank you very much for the info, the divergence of 520nm 1 watt lasers is far worse than I had imagined they could be. I have some M140 diodes and didn't realize they were that bad either.

steve001 · Dec 19, 2014

Laser Project said:
You want a 10 degree wide beam? Maybe you can just have a variable focus lens and just do it that way, take it out of focus until the beam is 10 degrees wide.

Use this app gausian beam rev 2.0.xls it has a graphical presentation.

Alaskan · Dec 21, 2014

Lord, I don't understand much on that page, I need to find a basic course on laser optics.

steve001 · Dec 24, 2014

Laser Project said:
Lord, I don't understand much on that page, I need to find a basic course on laser optics.

I can help.

Alaskan · Dec 26, 2014

Let me study more and come back to you, thank you for your offer to help.

steve001 · Jan 1, 2015

Alaskan said:
Let me study more and come back to you, thank you for your offer to help.

Good to study, but you don't really need to learn more to use and understand that app.

Beam double expander

nikosb

0

Alaskan

0

Hemlock_Mike

0

nikosb

0

Hemlock_Mike

0

lazeristasUVISIR

0

Alaskan

0

lazeristasUVISIR

0

Alaskan

0

lazeristasUVISIR

0

Alaskan

0

steve001

0

Alaskan

0

steve001

0

Alaskan

0

steve001

0

Online statistics

Forum statistics

Share this page