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12-15-2014, 06:30 PM #1
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nikosb
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Beam double expander

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?

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12-16-2014, 02:24 AM #2
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Re: Beam double expander

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.
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12-16-2014, 02:56 AM #3
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Hemlock_Mike
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Re: Beam double expander

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
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Last edited by Hemlock_Mike; 12-16-2014 at 03:32 AM.

12-16-2014, 03:29 AM #4
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nikosb
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Re: Beam double expander

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.

12-16-2014, 04:05 AM #5
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Re: Beam double expander

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
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12-16-2014, 07:37 PM #6
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lazeristasUVISIR
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Re: Beam double expander

Quote:
 Originally Posted by nikosb 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.
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12-17-2014, 04:26 AM #7
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Re: Beam double expander

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.

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To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

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Last edited by Alaskan; 12-17-2014 at 05:49 AM.

12-17-2014, 01:38 PM #8
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lazeristasUVISIR
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Re: Beam double expander

Quote:
 Originally Posted by Laser Project 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/technica...beam-expanders
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12-17-2014, 04:36 PM #9
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Re: Beam double expander

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.
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To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

Useless troll fighting.
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High resolution of my avatar: https://ibb.co/fWOhXF

Last edited by Alaskan; 12-17-2014 at 04:53 PM. Reason: stupid is as stupid does

12-19-2014, 02:03 PM #10
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lazeristasUVISIR
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Re: Beam double expander

Quote:
 Originally Posted by Laser Project 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
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12-19-2014, 04:24 PM #11
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Re: Beam double expander

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.
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To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

Useless troll fighting.
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12-19-2014, 07:54 PM #12
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Re: Beam double expander

Quote:
 Originally Posted by Laser Project 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.

12-21-2014, 07:28 AM #13
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Re: Beam double expander

Lord, I don't understand much on that page, I need to find a basic course on laser optics.
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Sam's Laser FAQ: Sam's Laser FAQ: Welcome Page

RHD's Relative Perceived Brightness Calculator. Compare brightness @nm: http://lsrtools.1apps.com/relativebrightness

To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

Useless troll fighting.
.........................
http://imgbb.com

High resolution of my avatar: https://ibb.co/fWOhXF

12-24-2014, 03:02 AM #14
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Re: Beam double expander

Quote:
 Originally Posted by Laser Project Lord, I don't understand much on that page, I need to find a basic course on laser optics.
I can help.

12-26-2014, 06:14 AM #15
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Re: Beam double expander

Let me study more and come back to you, thank you for your offer to help.
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Sam's Laser FAQ: Sam's Laser FAQ: Welcome Page

RHD's Relative Perceived Brightness Calculator. Compare brightness @nm: http://lsrtools.1apps.com/relativebrightness

To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

Useless troll fighting.
.........................
http://imgbb.com

High resolution of my avatar: https://ibb.co/fWOhXF

01-01-2015, 10:41 PM #16
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Re: Beam double expander

Quote:
 Originally Posted by Alaskan 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.

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