I How do I stretch a laser from a beam into a sheet?

[LightningInAJar]

TL;DR

How do I stretch a laser from a beam into a sheet? Cylindrical lens?

I would like to fan out a laser pointer's beam into a sheet of light, so basically stretch it along a single axis so it creates a plain. I wasn't sure if a cylindrical lens was the right tool for the job? And I figure I might need a few laser pointers all piped into it to ensure enough light is left after it is stretched.

 

[DaveE]

TL;DR: How do I stretch a laser from a beam into a sheet? Cylindrical lens?

I wasn't sure if a cylindrical lens was the right tool for the job?

Yes, most likely. Maybe two if you want 1D collimation.

 

[sophiecentaur]

TL;DR: How do I stretch a laser from a beam into a sheet? Cylindrical lens?

And I figure I might need a few laser pointers all piped into it to ensure enough light is left after it is stretched

A very cheap laser level will have an optional end cap for the output which gives a projected straight line. I used to have one but I never actually looked at what was in that cap. (Shame on me!!!! - very unPF)

TL;DR: How do I stretch a laser from a beam into a sheet? Cylindrical lens?

stretch it along a single axis so it creates a plain.

Reading this again suggests you need a spreader with circular symmetry. A cylindrical lens would only work along one axis (as my quoted laser line source, above). A simple diffuser could work but spreading the laser power over a large area would make it very dim. OR do you mean you want to produce a 'sheet' as the light goes through a smoky medium?

 

[tech99]

I think you might use a Galilean telescope arrangement. First a concave lens to expand the beam diameter, followed by a large cylindrical lens to spread the beam in the one plane.

 

[Baluncore]

Use a cylindrical lens with a vertical axis, to convert the dot on a wall from a laser level, into a horizontal line on the wall.

 

[tech99]

The initial beam from the laser must have finite diameter for it to work I think, that is why I suggested a first, round concave lens as a spreader. The final lens need to be concave cylindrical.

 

[Ibix]

Worth asking why @LightningInAJar wants this, to put some constraints on reasonable solutions.

 

[DaveE]

The initial beam from the laser must have finite diameter for it to work I think, that is why I suggested a first, round concave lens as a spreader. The final lens need to be concave cylindrical.

It would be quite unusual for a laser to be converging away from the exit. Normally the beam waist will be near the aperture, and in expensive lasers at a specified location. It will have a predetermined diameter. Although all of this gets messy with cheap or diode lasers. in any event it's the (sort of) far field divergence in the two planes that is the real point here.

As I understand the "sheet" that the OP wants, it should have increased divergence in one plane, and minimal divergence in the other plane (normal to the sheet). So, you could add a telescope in the normal plane (for a thicker sheet), but I wouldn't add a simple lens. That would create a "wedge".

Also, this is probably a diode laser which will have a fast and slow axis (i.e. different divergence in orthogonal planes). So the orientation of the source may be worthwhile consideration.

 

[LightningInAJar]

A very cheap laser level will have an optional end cap for the output which gives a projected straight line. I used to have one but I never actually looked at what was in that cap. (Shame on me!!!! - very unPF)

Reading this again suggests you need a spreader with circular symmetry. A cylindrical lens would only work along one axis (as my quoted laser line source, above). A simple diffuser could work but spreading the laser power over a large area would make it very dim. OR do you mean you want to produce a 'sheet' as the light goes through a smoky medium?

No smoky medium. I would like to create a plain of laser light to take video of rain water or snow falling through it as a little art project.

 

[DaveE]

No smoky medium. I would like to create a plain of laser light to take video of rain water or snow falling through it as a little art project.

You could also consider scanning a 1D beam in a plane faster than your shutter speed or the rain drops. This may be easier. Something like a reflection off of polished faces of a hexagonal nut (the mirrors) mounted on a motor shaft. You may have to fiddle with aliasing issues depending on the speeds.

 

[renormalize]

You could also consider scanning a 1D beam in a plane faster than your shutter speed or the rain drops. This may be easier. Something like a reflection off of polished faces of a hexagonal nut (the mirrors) mounted on a motor shaft. You may have to fiddle with aliasing issues depending on the speeds.

Yes, planar-scanned lasers are often used for special-effects in movies. An example is this shot from the opening of Aliens, where a robotic drone searches for Ripley in her cryo-chamber:

 

[phinds]

I would like to fan out a laser pointer's beam into a sheet of light, so basically stretch it along a single axis so it creates a plain

a plain WHAT?

I think you mean plane.

 

[tech99]

The "mirror drum" must be very perfect optically, difficult to achieve I think.

 

[sophiecentaur]

No smoky medium. I would like to create a plain of laser light to take video of rain water or snow falling through it as a little art project.

That (fan-out) would be a line when projected on a screen. Sounds like you want the laser level gizmo I used to have. Have a look on eBay; always worth a try.

A single narrow slit would be a suitable solution with a spread of sinx/x distribution. But the beam would need to be focussed small in the plane of the slit of the light would be attenuated / largely blocked.

I think you mean plane.

His meaning was plain. tadaahh

 

[sophiecentaur]

You could also consider scanning a 1D beam in a plane faster than your shutter speed or the rain drops. This may be easier. Something like a reflection off of polished faces of a hexagonal nut (the mirrors) mounted on a motor shaft. You may have to fiddle with aliasing issues depending on the speeds.

Or a very light vibrating mirror on a pivot. Frequency wouldn't need to be exceptionally high to allow the drops to have a long exposure. A compromise between brightness and smearing. A loudspeaker cone could drive it at perhaps 10kHz ir even much less.

 

[Baluncore]

The "mirror drum" must be very perfect optically, difficult to achieve I think.

If you want a polygonal mirror, find yourself an old laser printer.

Traditional laser printers have a rotating polygonal mirror with an optical system to illuminate the drum. More recent LED printers do not.

 

[sophiecentaur]

a rotating polygonal mirror

Quite a thought. Laser printers were developed with an amazing amount of ingenuity and, like tape recording and colour TV, they really shouldn't work. If you could make use of all the cannibalised mechanism with very little effort to direct the beam then it would probably give exactly what's wanted. If the OP really needs that sort of spec then it might be doable.

But a simple reciprocating reflector would cost very little and the technology probably exists in all our houses as we speak (write)_.

 

[LightningInAJar]

You could also consider scanning a 1D beam in a plane faster than your shutter speed or the rain drops. This may be easier. Something like a reflection off of polished faces of a hexagonal nut (the mirrors) mounted on a motor shaft. You may have to fiddle with aliasing issues depending on the speeds.

So basically a handheld barcode scanner?

 

[LightningInAJar]

What is the least expensive solution without and with moving parts? I already returned a useless lens to Edmund Optics. I don't want to spend more than needed.

 

[sophiecentaur]

I already returned a useless lens to Edmund Optics. I don't want to spend more than needed.

You have my sympathy BUT why spend that sort of money on an initial project? Edmund Optics supply high end users. Why not look through my fave eBay or the local second hand market? If you have calculated the focal length you need for your lens then a used camera lens could well do the trick.
I can well understand your 'no moving parts' stipulation and using a small mirror pushed by a (used again) loudspeaker involves 'minimally moving parts' - certainly no rotation.

 

[LightningInAJar]

You have my sympathy BUT why spend that sort of money on an initial project? Edmund Optics supply high end users. Why not look through my fave eBay or the local second hand market? If you have calculated the focal length you need for your lens then a used camera lens could well do the trick.
I can well understand your 'no moving parts' stipulation and using a small mirror pushed by a (used again) loudspeaker involves 'minimally moving parts' - certainly no rotation.

I initially got a cylindrical lens on Amazon for under $8. It didn't work at all.

 

[DaveE]

You could just buy a laser level. They've already figured it out for you. OTOH, they won't be as bright as you want because they don't want to spend extra money and/or hurt people.

Here's my 5 minute experiment.

 

[TSny]

You might experiment with fanning out the beam by reflecting off a smooth cylindrical surface. Here, I used a ceramic mug.

 

[LightningInAJar]

You might experiment with fanning out the beam by reflecting off a smooth cylindrical surface. Here, I used a ceramic mug.

That is interesting. How much light do you think gets absorbed by the mug? I wish I could visualize how that happened. Looks like you reflected 90 degrees off of it?

 

[LightningInAJar]

You could just buy a laser level. They've already figured it out for you. OTOH, they won't be as bright as you want because they don't want to spend extra money and/or hurt people.

Here's my 5 minute experiment.

That is with the laser level giving a somewhat vertical line beam?

 

[TSny]

That is interesting. How much light do you think gets absorbed by the mug?

I don't know. A highly reflective metal surface or mirror would not absorb very much.

I wish I could visualize how that happened. Looks like you reflected 90 degrees off of it?

Each ray of light in the beam obeys the law of reflection at the curved surface.

 

[DaveE]

That is with the laser level giving a somewhat vertical line beam?

Vertical and horizontal in this case.

 

[sophiecentaur]

I initially got a cylindrical lens on Amazon for under $8. It didn't work at all.

Just any old concave lens will not do. I saw several versions of the same on eBay thing so they are clearly for a particular purpose.
is this the sort of thing they delivered? (eBay ad)

But seriously, why not go for a cheap laser level?

they won't be as bright as you want because they don't want to spend extra money and/or hurt people.

A fan-out will reduce / eliminate the risk of eye injury by a massive factor.