Beam size meaurements

<rant>

Beam size measurements. It's the easiest thing to do! All it requires is a device that measures length, ruler, tape measure, calliper, meter stick, anything! It's not like a power measurement that requires a 200$ LPM.

Yet I rarely see this included in reviews & when people are selling lasers. Buyers are equally as bad, hardly anyone asks for the beam size when buying a laser.
Take Lazerer for example, they can afford to invest in an 200$ LPM and they provide power measurements for the lasers they sell but they can't invest in a 2$ ruler and provide beam size and divergence measurements?
A good example of this are these stick/crown upgrade lasers. They have MASSIVE beams! A quality 100mW laser with a tiny beam looks just as bright!
LZSK - Stick 532nm 500mW High Power DPSS Green Laser Pointer

Everyone is always after "POWER POWER POWER" but what really makes a beam bright and beautiful is power density, and that is dependent on the beam size & divergence as well as the power!

Almost every review I see, even by vets, don't include the beam size, but include LPM charts. Just today I was looking at high power 532nm laser reviews, and not ONE person had included the beam size, usually high power 532nm lasers have ugly beams, and having a tiny TEMOO beam is worth much more than having a few hundred more milliwatts.

What I'm trying to say is please stop this trend of only looking at a lasers output. There's much more to a quality laser than having the highest power. Take the time and post a beam size & divergence measurement with your laser when reviewing it or selling it.

</rant>

P.S. Here's an easy tool to calculate divergence! pseudonomen137's JScript mRad Calculator

Thanks for that, I will update my review later tonight with the beam size
:thanks: again, that would have gone completely unnoticed by me

JollyKillBill said:

Thanks for that, I will update my review later tonight with the beam size
:thanks: again, that would have gone completely unnoticed by me

Click to expand...

Thanks for adding it to your review! A lot of people don't think to add this because it's rarely talked about

I agree 101 % with ARG-L , like my o-like bla bla 400 mW crown bla bla it's all bright and lots of power but the beam/dot is really UGLY after a meter or 20 haha , indoors it's awesome for a beam show but after 50 or 100 feet it's not much more then a green blob of 532

Wouldn't that all depend on the distance from the Laser
and type of lens used not to mention if the beam is round
(Gas) or from a Single Mode or Multimode Laser and if you
measure it through Laser Safety Goggles.

It could be difficult to accurately measure the beam diameter
of a High powered Laser.

Do you measure ALL of the beam or just the Brightest areas??
There would need to be a Beam Diameter Measurement Standard
so that all quoted Beam diameters were measured in the same
exact way.

If not you could be comparing Oranges to Apples...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Hi,

here is a Wiki link...mmmm Gaussian beam - Wikipedia, the free encyclopedia

OK, so if we do that, we all get apples, not oranges.... but sometimes a banana is close enough (and I like bananas).
As long as the review details the measurement method, rule, caliper, whole beam / brightest / distances etc, it will give some meaningfull infomation that would be useful to see in a review, (even if it is not traceable back to national standards!)

My 2p:beer:

Yup, that's the ticket multimode.


That is the area to be measured on TEM00 beams. Same applies to multi-mode beams, measure around brightest area.

Cant wait to calculate my divergence tonight! Thanks Arg! +1 for looking at other things then power, etc.

Jerry has a point though: it's one thing to be able to measure the width of the beam using a beam profiler, it's another to eyeball the 1/e^2 intensity beam radius on the wall spot.

Probably the best method would be to just take a photo of the spot at a measured distance and let the reader decide.

True enough, it's still easy enough to take a photo of the spot using goggles as a filter with a ruler, I don't know why people don't include it more often.

Hmm, well, mostly laziness. For me it's definitely laziness. I mean the reason why I don't include it.

I do tend to ask when buying, and also say so if the beam is unusual when selling. I think to date, with several dozen sales, only 1-2 people ever asked for beam diameter and divergence.

Also, unless the laser has a fixed lens, the user can focus it to whatever beam spot that is desired. For 532nm lasers coming from CNI or something, having the mrad is a good thing, and quite doable, but I don't know how useful it is for hobby-made lasers. Even for Lazerer's lasers it doesn't matter too much because they're all going to have the same basic divergence of any other green laser.

Bionic-Badger said:

Jerry has a point though: it's one thing to be able to measure the width of the beam using a beam profiler, it's another to eyeball the 1/e^2 intensity beam radius on the wall spot.

Probably the best method would be to just take a photo of the spot at a measured distance and let the reader decide.

Click to expand...

What I was getting at was that not having a standard of how
to accurately and repeatedly measure a beam diameter that
any resulting measurements would be near useless.

I would suggest stating the distance from target...
And taking a picture of the beam on some chosen standardized
graphed paper of a standard color.

It would be up to the person doing the tests to adjust the lens
to the smallest beam.

Then as you say.. let the buyer decide by the photo.

But you still need a predetermined standard or the results will
be all over the place. I know my vision isn't isn't as acute as
it once was.


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

I approve of this thread... nice post ARG. When I measure beam profile (cross-section), I first expand the beam with a telescope (even a magnifying glass works though) and observe the structure of the beam. Here's an example of a beam from a 1W CNI 532nm lab-style laser:



You can see that there is some structure within the beam, hot spots and cold spots, which means it's not entirely TEM00.. this is what the Chinese suppliers refer to as "near TEM00" but technically it's multimode.

Here's TEM00:



The center of the spot is fully saturated, the beam is nice and round.

Ideally the best way to measure profile is to use a device that's meant for that specifically, but expanding the beam is an easy way for the hobbyist to check their lasers.

Once I've expanded the beam to see it's profile, then I remove the telescope that I used to expand and measure the divergence. It's possible to measure the beam diameter without knowing the exact structure of the beam cross-section, and then calculate using those measurements. Once you've done these 2 things you'll have some pretty detailed knowledge of the beam in question.

What is a good divergence number for a 380mW-320mW green Laser?
My Wicked Laser Krypton is 1.0mRad @ 120-110mW and 2.0mRad @ 380-320mW

JLM said:

What is a good divergence number for a 380mW-320mW green Laser?
My Wicked Laser Krypton is 1.0mRad @ 120-110mW and 2.0mRad @ 380-320mW

Click to expand...

Great is around .6mrad. Good is around .8mrad. 1mrad is about average, 1.5-2mrad is typical of those stick/crown upgrade lasers.