Widening A Laser Beam

I’ve been playing around with a laser pointer, and I want to try a couple of things with it, but the beam’s not as wide as I’d like. Any easy way I can get the beam wider? Yeah, I could concievably use LEDs instead of the laser pointer, but I’m going for maximum dork factor here, and that means frickin’ lasers! :smiley:

AFAIK, usually with diode pointer-type lasers, the beam starts off rather wide and non-laserlike and optics are used to narrow (collimate) the beam. If there’s a lens visible on your diode aperture, see if you can remove it and get the desired results.

You want a beam expander. The one I linked to, is too expensive, but the there’s a bit of a description of the needed optics. You might be able to pick up a fiber optic based expander at a nearby rock show, or whip one up out of 3 conventional lenses (1 to expand, and two to recollimate).

You could try to use a telescope in reverse, if you have a telescope. Shine the laser into the eyepiece.

That’s a little too large for the application I have in mind.

You can use two spherical glass beads as a crude beam expander.

You’ll have to play with the spacing between the beads and the spacing of the laser aperture to the first bead, but it will do the trick. If you’re analytically skilled and know the properties of your beam, you can work out the spacing beforehand.

You’ll also need a good way to mount everything; a rigid tube with cylindrical shims is a good idea for starters.

The good news is that the beads only need to be about 20-25% larger in diameter than the diameter of the beam you want.

Look at these for starters. You can probably find them a lot cheaper, though.

Sorry - forgot also to mention that you’ll need beads of two sizes, the larger one a bit bigger than your expanded beam diameter, and the smaller one a bit bigger than the size of the laser aperture.

Tuckerfan, what do you mean by “wider”? If you want the beam to fan out rather than travel in a straight line, you can either strip the lens off the front of your pointer (which can be hard to do right, though it’s worked twice for me), or you can point it through another lens. If you want the beam to travel in a straight line but be thicker everywhere along that path, you want the beam expander or telescope that Squink and ZenBeam are talking about. A telescope is a special case of a beam expander. The expansion ratio and the magnification are the same number.

Intriguingly, there’s a limit to how thin the beam can be and how little it can fan out, and the thinner it is the more it has to fan out, and vice versa. This gets worse the longer the wavelength is. On the other hand, if you want it wider and also fanning out more, that’s easy to do - in fact to some degree the challenge is usually to not do that.

jnglmassive, all diode lasers including all the ones in pointers produce true laser light, in the sense that it is a stimulated emission process. And it’s all synchronous, all in phase or all in a small integer number of phases across the beam. But as it comes from the diode, it’s not a beam, it’s spreading from an almost perfect point source. “Laser” means how the light is generated, not whether it’s a beam. You’re right - there’s a lens in there to turn that fan into a beam.

For simmple, noncritical applications, you can also purchase beam expanders that are holographs of the fancy opticals. When a laser beam shines through them, it gets reflected around by the silver emulsion and emerges with essentially the same properties as it would have from the original gear. I suspect that Edmund Scientific would be into holographic optical gear in a big way. They’ve always had a big stock of optical demos (and discount optical gear, albeit not nearly as cheap as the stuff at the good local electronics surplus shops). You can also often get them cheap in surplus companies advertised in hobbyist magazines from “Nuts and Bolts” on up.

What I mean by “wider” is that I want the beam to be a larger diameter, so that instead of throwing a spot on the wall about a 1/4" of an inch in diameter, it throws one an inch or larger, and just as round. I tried stripping the lens off of two pointers, but ended up destroying them in the process (good thing I got those two for free, the next ones I’m going to have to pay for).

KP, do you have any links? All the electronics surplus places around here have shut down, and it’s a bear trying to find any decent electronics mags in this town.

I’m trying to do this on the cheap (if I can get away with less than $50 total in the project, I’ll be a happy camper). Anybody know if there’s an easy way to wire up the laser in a CD player? I’ve got one that no longer tracks, and I’ve thought about cannibalizing that, but I’m not sure of what the power requirements for the laser are. The player’s a Sony CDP-491.

CD players use infrared lasers, so that won’t help unless you’re trying to pester bees or people with camcorders. If you’re going to cannibalize something, use an old DVD player.

A laser diode does not act like a point source. It is indeed a beam, with a larger than average divergence angle which is collimated by the optics that make up the lens. The real problem with a laser diode is that the beam is very asymmetric when it exits the semiconductor, which is why without the optics it spreads out into a fairly elliptical shape that’s much longer in one dimension than the other. The lens collimates that to try and reduce the divergence and turn the beam into a closer approximation to a gaussian shape.

The beam still has some divergence though, so if you just want a bigger spot on the wall you can move farther away from it. I assume that this isn’t acceptable for your desired application. You can make a beam expander out of two cheap lenses, if you can get your hands on some. The only thing you need to make sure is that they’re different focal lengths (in fact the expansion ratio will be the ratio of the focal lengths). You can get lenses for ~$25 a piece at www.edmundoptics.com, or perhaps more cheaply at thorlabs or other sites. If you just want to expand the beam at one point (i.e. you don’t need it to be thicker along the entire path of propogation) you only need one lens, or one of bughunter’s glass beads.

The lasers in CD players probably won’t do you much good, as they operate in the near-IR (~780nm iirc), which means you won’t be able to see it without some sort of IR viewer or fluorescence card.

Yeah, I said three because I’ve used a home-built, 2 lense, collimator, along with another lens to enlarge the beam.
Edmund industrial lenses are nice, but you pay for that. Edmund Scientifics has some cheaper ones that should do the job. (Their online catalog isn’t so good, get an actual paper catalog).

>What I mean by “wider” is that I want the beam to be a larger diameter, so that instead of throwing a spot on the wall about a 1/4" of an inch in diameter, it throws one an inch or larger, and just as round.

Yes, but, which way? Do you want it to be an inch regardless of how far away you stand, or do you want it getting bigger the further away you are? An inch regardless means you want a beam expander. An inch getting bigger means you want a single lens.

>A laser diode does not act like a point source. It is indeed a beam, with a larger than average divergence angle which is collimated by the optics that make up the lens.
This distinction is getting hazier and hazier, but typical laser diodes emit a squished cone of light maybe 20 degrees wide that appears to come from a point of micrometers in size. You could call that a beam with a large divergence, but you could also certainly call it light coming from a point.

Ideally, I’d like it to stay an inch it’s whole length, but it’s primarily a cost issue. And I’d post exactly what I intend to use this for, but it’s part of a surprise for an old friend who sometimes lurks here, so I don’t want to run the risk of them seeing it.

Tuckerfan, forget the mumbo jumbo. Assuming this is a cheap, throwaway pointer and also assuming you are down to the bare circuit board, pry/remove the collimating optic from in front of the diode’s aperture and the beam will be nice and diffused. Every visible laser diode I’ve ever seen was in a sturdy brass housing and sometimes the optics are threaded in with a slot for a screwdriver at the front. The beam might be a bit oblong but bright and probably just what you’re looking for.

I tried that last night and ended up destroying two in the process. Once I pulled the lens off, the laser stopped working and putting it back in front didn’t fix the problem, so I’m guessing I damaged the diode or the circuit board.


At least now you have a few to study and not worry about breaking…more. How is the optic attached and is there an easy way to get the optic off? I’ve found that the hardest part of getting the optic out of the diode is getting the PCB out of the pointer body. The boards [iare* out of the housing, right?

Getting the PCB out was no problem, the problem was getting the optic off. In both cases it was attached to a seperate, smaller housing, which covered only the diode. That housing, I just couldn’t remove (well, actually I did, that’s when they broke). The one pointer, the lens appeared to be glued to the inner housing, while I was trying to pop the lens out, the PCB and diode fell out, and refused to work. The other pointer, was as you described with the screw slot in the front. Try as I might, I just couldn’t get it to loosen. I gently clamped it in a bench vise, and tried turning it, at that point, the housing twisted and buckled and the PCB and diode fell out. With this one, it looked like one part of the diode had pulled free from one of the wires connecting it to the PCB. Don’t have the necessary gear to fix that, so it joined it’s brother at the bottom of the trash can (though I did try to get it to work, first).

So two different types of pointers and neither one a winner, hmm?

I guess it makes sense that these things are getting cheaper and cheaper in the quality department. All of the ones I have tinkered with had remarkably serviceable components. What usually went wrong was the little button would get stuck or misaligned and it wouldn’t work in the housing. I’d take them apart and…well, tinker.

I also have a green laser pointer (DPSS) that I took apart and was shocked to see a little potentiometer right there on the PCB. Turns out it was a power adjustment! Its hard to gage by eye but I’d say its about 40% brighter than the un-modded unit. I do have a second one of these to do the side by side analysis. The green ones are pretty cool. I can’t wait till the blues and then violets become more available and then affordable.

big laser fan