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Super wide-beam laser

adam1128

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Hi guys, I'm somewhat new to lasers, so please forgive my ignorance.

I'm working on a hobby project, and it needs a laser with a very wide + divergent beam. In short, it needs to be a similar beam width / divergence as a regular flashlight (e.g. say 1m wide at 3m distance, or wider?).

The idea is that it will be portable, and work just like an LED flashlight - only it will have the very narrow spectral width of a laser (1-3nm).

I've tried using an red LED flashlight (ultrafire 1505r), but the spectral width is too wide (20-30nm), which doesn't work for what I need it for.

To get that kind of narrow spectral width, it looks like I'd have to use a laser. But it's going to act like a flashlight, so I need a wide beam - not a small dot like I'd get with a typical laser pointer.

I've looked into beam expanders, but they seem to only go up to 10-20x, which is still way too narrow. Also, they seem to mostly keep the beam divergence low (if I've got that right - i.e. the beam although wide, doesn't get much wider with distance).

I've also looked into laser christmas light displays (which I think use diffraction gratings to spread the beam into multiple dots). This isn't ideal, as I really want an even, wide beam, as opposed to many dots. Also, I'm not sure if the diffraction gratings will alter the wavelength too much. If they increase the spectral width, or then that won't work either.

My final thought was to use something like a monochromatic laser projector: i.e., a system the (I guess) uses a mirror to 'draw' the laser beam over an area. Other than commercial RGB laser projectors, I can't find much. Given the thing needs to be portable (eventually), battery powered and not cost the absolute earth, this probably isn't a sensible option either.

Any help or suggestions would be really, really appreciated.

Thanks,
Adam
 

diachi

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Hi guys, I'm somewhat new to lasers, so please forgive my ignorance.

I'm working on a hobby project, and it needs a laser with a very wide + divergent beam. In short, it needs to be a similar beam width / divergence as a regular flashlight (e.g. say 1m wide at 3m distance, or wider?).

The idea is that it will be portable, and work just like an LED flashlight - only it will have the very narrow spectral width of a laser (1-3nm).

I've tried using an red LED flashlight (ultrafire 1505r), but the spectral width is too wide (20-30nm), which doesn't work for what I need it for.

To get that kind of narrow spectral width, it looks like I'd have to use a laser. But it's going to act like a flashlight, so I need a wide beam - not a small dot like I'd get with a typical laser pointer.

I've looked into beam expanders, but they seem to only go up to 10-20x, which is still way too narrow. Also, they seem to mostly keep the beam divergence low (if I've got that right - i.e. the beam although wide, doesn't get much wider with distance).

I've also looked into laser christmas light displays (which I think use diffraction gratings to spread the beam into multiple dots). This isn't ideal, as I really want an even, wide beam, as opposed to many dots. Also, I'm not sure if the diffraction gratings will alter the wavelength too much. If they increase the spectral width, or then that won't work either.

My final thought was to use something like a monochromatic laser projector: i.e., a system the (I guess) uses a mirror to 'draw' the laser beam over an area. Other than commercial RGB laser projectors, I can't find much. Given the thing needs to be portable (eventually), battery powered and not cost the absolute earth, this probably isn't a sensible option either.

Any help or suggestions would be really, really appreciated.

Thanks,
Adam

I'd probably just use a laser diode without any focusing lens, or the focus adjusted all the way to spread the beam out.

If you don't use a focusing lens you'll still need to place some sort of optical window in front of the diode to prevent contaminants from getting on the diode.
 

steve001

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A single divergent lens will work. Single lenses are also called Singlets.
 

BowtieGuy

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Here is a 503nm with a 3 element lens adjusted to probably half as far unfocused as it will go. Or just go without as diachi mentioned.


 

diachi

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A single divergent lens will work. Single lenses are also called Singlets.

You mean a concave lens...? :thinking:

A single convex lens would work too, but it'd also allow you to collimate the beam.
 

CurtisOliver

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I don't need to repeat what the others said. They already stated their advice well. My concern is more 'why'? The thing I usually associate portable diverging lasers, is that of similar requests to build laser dazzlers. Please assure us that this isn't your intention.
 

diachi

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I don't need to repeat what the others said. They already stated their advice well. My concern is more 'why'? The thing I usually associate portable diverging lasers, is that of similar requests to build laser dazzlers. Please assure us that this isn't your intention.

Yeah, I'd like to know what you intend to do with this too, and why you need such a narrow spectral width. :thinking:
 

paul1598419

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This seems like an unusual request as I can't think of a reason one would want such a divergent beam at a narrow spectral width. You didn't mention a wavelength either. Is that not important? If this is to be used to temporarily blind someone, I doubt anyone here would want to help you.
 
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Yeah, I'd like to know what you intend to do with this too, and why you need such a narrow spectral width. :thinking:
Me too. Whats the application?

I can think of one application that could use a very wide divergence that is acceptable (ie not a weapon).
 

adam1128

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Hi guys,

Firstly, thanks so much for all of the help. It's really generous and I really appreciate it. Secondly, I'm really not building a weapon! I'm doing a PhD in machine learning, and doing some experiments with computer vision. I'm having trouble with the algorithms, so wanted to try doing some clever optical filtering to help them out.

Except I don't know much about optics. And if it's actually going to dazzle people that's a real problem!

Anyway, it sounds like perhaps a concave lens might be a possibility. I'd also found diffusers. They also seem to get rid of speckle, which is something that would be important (as it might well confuse the algorithms). E.g. https://www.rpcphotonics.com/engineered-diffusers-information/

They are pretty expensive, and I imagine I might not need something so precise.

Any thoughts on whether a diffuser or concave lens would be better?

I've also looked into how laser projectors work - seems like they use phospur diffusers, maybe even rotating diffusers. That might be overkill - I don't need to *totally* remove speckle.

In short, if I can end up with a nice diffuse area of light that appears smooth to the user (so a person could use it as a functional flashlight, and not really notice the difference to say a monochrome LED flashlight) that would be great. I've looked into laser projectors as they basically do what I want - turn laser light into a wide, smooth 'usable' (and not dangerous!) light something like a normal lamp (but much more efficient?) and with nice spectral properties for computer vision.

Thanks again for the help!

Adam
 

paul1598419

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Speckle is just the interference that occurs when laser light interferes with itself when seen on a nonreflective surface. Because the surface is different on a microscopic level from that which is immediately next to it, it can cause in and out of phase differences to occur in the interference patterns as your eyes move with respect to the surface. This is often diffused when the beam is not collimated, so I am wondering if this is a real problem for you. Using any lens you can cause the beam to become wider and, thus diverge at greater or lesser angles depending on how far from the laser emitter it is positioned. This, alone, should remove the speckle interference you are worried about.
 

BobMc

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Something you can try with any 5 dollar laser. Take the lens out and turn it around and put it back in. It will give you a colored flashlight beam, won’t be perfectly round, but round-ish. Still quite intense, so be careful with it. Welcome and be safe.
 
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paul1598419

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Diffuse laser is also good for viewing old
holograms.
HM
Yes, but only transmission holograms made with the same wavelength. Reflection holograms set up standing waves of light of only the same wavelength as used to make it from white light. I enjoy making them as you don't need a laser to reconstruct the image.
 

Alaskan

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