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Hmm. Mine always put out a line no matter what power. heh. :p
Hmm. Didn't say it doesn't make a line. heh. :p

What I said was that the beam properties are quite a bit better at low power than high.

If you have one of these diodes on a flexmod (or any analog driver) you can see at the aperture that, at low powers (around 100-200mW), the beam is a very tight line, with comparatively low near and far-field divergence. As you increase power you can see that the line broadens and more structure appears, and the divergence gets worse. You can also see this with an Arctic when comparing high and low power.
 

qumefox

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Heh, my LG Polaris 150mW 445 is the most over-built, under-driven 445 i've ever seen. Bigger than a baby's arm, corrective optics, and still very striking output. :) Funny thing is it's one of my favorite lasers.
I've always wondered about these. Do they have actual corrective optics, or is the output simply passed through an aperture that chops off the outside edges of the line?
 

aryntha

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I've always wondered about these. Do they have actual corrective optics, or is the output simply passed through an aperture that chops off the outside edges of the line?
Actual corrective optics. The fast axis is "folded in", and ends up looking more like my multimode HeNe, complete with 'circular' multimode patterns and all. It is certainly NOT just a chop.

I actually did a review on it here. I have the CNI uncorrected 1W version, and the LG Polaris 150mW corrected version, so I can compare side by side.

It's definitely not just a chopping aperture.
 

qumefox

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Let me guess. Forum lag making you double post. I've had to delete a couple of mine over the past few days that ended up with duplicates heh.
 

aryntha

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They're actually in the thread I just linked up there with my review... May want to check my math on it but I came up with around 0.8mRad average. (Please do allow some wiggle room for measurement error, with a ruler and all. :p )
 

aryntha

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Let me guess. Forum lag making you double post. I've had to delete a couple of mine over the past few days that ended up with duplicates heh.

Yup, just nuked it. Avery's been upgrading and changing stuff.

In any case, I do wish CNI was putting similar optics in their 635s. They may not be able to, due to the output pattern though. I do wish we could figure out what they're doing on our own so we could build similar things into our 445 builds though.
 
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qumefox

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I believe you can get circular diffraction patterns using an aperture. It just depends on the maths. diameter of aperture, distance from diode, etc. I just think this would explain why the corrected lasers weren't available over 400mW. There are only three ways to correct the beam on these that i'm aware of. Anamorphic prism pair, cylindrical lenses, and an aperture. Neither of first two have any kind of power limitation when using glass optics aside from the normal losses you get with optics. Only the aperture method.. which is also the cheapest, results in a large loss of power.

I'll try to go through the appropriate maths and make an aperture for one of my 445's when I get a laser workspace that's larger than 30"x30" heh. And see what the output looks like.
 

aryntha

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From what I understand, the lenses *are* acrylic. So I'm not sure. I got this information from both Laserglow and CNI; but while it could be wrong, the way the beam looks at aperture exit tells me this isn't just a chopoff too.

Upon aperture exit, it's pretty much perfectly round and wide, with circular multimode patterns -- nothing like the other 445s. I was a skeptic too; LG didn't give me any kind of discount on the laser to review it (Still have yet for that to happen, ever :p ) - and I think if you saw it in person (which you probably will at some point) you'd agree that there's something else going on there.
 

benmwv

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I didn't even know you could correct a 445 with an aperture. I though that a lot of the lines were overlapping in the center of the output, so it would still come out bad :thinking:

I'm gonna have to experiment with this. About how big of an aperture would be used, just as a rough estimate? Small like .5-1mm dia. or more like 2-3mm?

Before or after lens?
 
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Really an aperture doesn't help much. It can help at certain points between near and far-field, but it won't help truly correct the beam as a whole. A lot of the garbage still gets through. The best methods I've seen to circularize (not just correct) an astigmatic laser beam are spatial filters and optical fiber. There's a chance that the polaris uses fiber, but I doubt it due to the irregular power distribution across the beam spot profile. The output of a singlemode fiber is very evenly distributed and almost perfectly round.

I don't think they're using a spatial filter either, but they could be. It certainly would help explain the power loss. A spatial filter is very similar to an aperture in that is consists of a hole, but it differs from a normal aperture in that it's a microscopic hole. To remove unwanted output from a laser beam using a pinhole, the beam must be focused to the finest point possible and a perfectly round hole precisely the size of a TEM00 focal point at the wavelength in question provided at the incoming multimode beam's focal point so that the beam passes through it. The result being that the focused multimode beam passes through the spatial filter, removing all other output besides what makes it through the pinhole, usually resulting in a close approximation of TEM00. MUCH more precise description here: http://en.wikipedia.org/wiki/Spatial_filter

Could also be a combination of prisms and cylinder lenses, which would also be lossy, and it would explain the imperfect roundness at various points along the beam. This is most likely IMO due to the ease of obtaining the lenses and the comparative simplicity of design. Fiber and Spatial Filters are usually very difficult to set up.
 
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qumefox

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A spatial filter is very similar to an aperture in that is consists of a hole, but it differs from a normal aperture in that it's a microscopic hole. To remove unwanted output from a laser beam using a pinhole, the beam must be focused to the finest point possible and a perfectly round hole precisely the size of a TEM00 focal point at the wavelength in question provided at the incoming multimode beam's focal point so that the beam passes through it. The result being that the focused multimode beam passes through the spatial filter, removing all other output besides what makes it through the pinhole, usually resulting in a close approximation of TEM00. MUCH more precise description here: Spatial filter - Wikipedia, the free encyclopedia
This was what I was actually meaning by aperture. I apparently just didn't know the correct terminology for it.

I don't think it uses anamorphic prisms because that results in an offset beam, and I don't think that's the case here unless everything is offset in the head and they're using itty bitty prisms.. which is a possibility. That leaves cylindrical lenses.. I have a set of dr.lava's so I can test that too. heh.
 
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I haven't used cylinders myself, only prisms, but if that's what can be obtained by just using cylinders I might change my game. I'm not hugely picky about beam shape myself since you can't tell too much about a beam when you're watching a projector, but low divergence is nice.
 
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Thank you, this is very nice to know. I would prefer to build a nice, stable beam for my first build. But I love the color of the 445. ;) Also, I'm curious what class laser this will be, I would like to use it as a spotting supplement for my telescope.
 




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