Bad Beams? | How divergent are lasers? 

"My method is more like......ghetto style" *This is a certified keychain laser classic*

Thanks for Pointing us in the right direction, and keeping us on the straight and narrow.

Will happily take ghetto setups as long as the units used are ISO units :)

4:30 the inverse tangent is irrelevant at the small angles and low precision you're using though, and in fact, in some contexts this type of divergence value is actually _assumed by default_ to be a sort of "first order small angle approximation mrad" rather than the "proper circular mrad with trig stuff". But basically, you can just get rid of the trig function entirely and substitute the parameter, cancel the 2's, and do (1.5 - .25)/1190 to get exactly the same value easily within your available precision.

At 3:00 - I get so excited every time I see speckles. Currently doing a research project at DTU Photonics regarding speckle, and hopefully my first article on the subject will be published within the coming months!

I never really thought how big of a factor laser divergence is until now when looking at long distances. Very interesting!

I'd like to hear more ...about those two subwoofers. ^^

Larger multimode diodes have a fast axis and a slow axis. Because of diffraction limitation physics, a smaller beam has a larger divergence (all else equal) which explains much of the reason the red diverges faster from the smaller initial axis. The beam correction optics principal is therefore simple: Expand the smaller (initial) axis to reduce its divergence.

You can use a mirrorless camera to capture the beam profile. Moreover, if you capture it in several planes you can completely recover the phase profile which is the all information you can get about the beam quality. Also you can improve the quality of the beam by passing it through a pinhole.

Would love a video on your entertainment system speakers!

0:43 the way you said “hi” put a beautiful smile of welcome to my face!!

1:36 Umm, lets talk about those 2 GIANT subs you have! : P

I was honestly just checking to see if you have any new videos up and I saw this! Thanks for the upload!

3:06 if you guys want to know what that integral equation means, it basically is just defining the beam intensity at some constant sigma, then you take the real number operator and then find the root of the intensity integral, then you define the x and y plane (since it is not like we have a complex Cartesian coordinate plane here) and then you define it if the intensity is zero, in which is the bottom part of the dividing of the two integrals, in the end you are just simply measuring a interval in integrals from the divergence at infinity, or at negative infinity. A more simple way of doing the exact same thing this equation does is to simply imagine the light as a hyperbolic wave function and then to measure the amplitude from there, sure it may be more expensive, but easier.

The divergence depends on the quality of the lenses used and collimation done well with distances of 100m from the laser. You can't determine the divergence if you don't make good collimation and don't use quality lenses.

Such an amazing video, keep up the good work!

You uploading today was the highlight of my day

I found it amusing to be watching this while I align a 4-laser system using the 13.5% measurement. Well done with the resources you had at hand.

Best method to measure the spots is to use a camera and export the beam profile. Then you can correctly identify the intensity and edges. A scale in pic allows calibrating the pixels to real world scale.

Many years ago, we set up a helium neon laser on a tripod at a friend's house, in the valley. As I recall it was only 5 mW, but it was physically pretty big. An aluminum cylinder maybe couple inches in diameter, and 8 or 10 long, and ran on a high voltage power supply. It gave a nice crisp red dot, not terribly bright. We then drove to the mountain peak, around 5600 feet, and maybe 15 miles away as the crow flies. Over the radio, we talked with him, as he tried to get the laser pointed at us. He first tried a handheld spotlight, so we'd know exactly where to look, but we never could see that. But he finally got that laser lined up and, while it was certainly not blindingly bright, it was without question at that point the brightest light visible in the city below. It would have been cool to hold up a big white sheet, to see if we could see a circle, but I don't think it would have been visible, even in the dark up there, what with all of the light pollution. And it very likely would have been a circle much bigger than a sheet at that distance. If the output was 2 mm, and we were what, maybe 20,000 meters away... Even a very good laser would have a lot of divergence. Would be interesting to calculate how big the "dot" would be if it was a 1 milliradian laser. It was pretty cool though. A fun night. Well, let's see, if it was 1 milliradian, and the initial size was 2 mm, the size at 20,000 meters would be... 40 meters? It was probably a bit better than that as it had come out of some old piece of equipment that was probably expensive back in the day lol.

Gotta love how the cheap laser has the best divergence

The best quality beams come from single spatial mode lasers like the ones you find in DVD burners. They need to have very high quality beams in order to read the disc accurately.

Wow another month has flown by. Thanks for the upload

What is absolutely beautiful is in the winter when you have large lazy snowflakes falling, shine a laser out a 2n story window cross the field. As snowflakes fall through the beam, they flash brightly. Very pretty. Best if there is very little wind and the flakes are large.

Nice Friday timing! Love the quality of your videos. Keep up the great work!

Great video! Finally i have something good to watch :D

Cool diffraction rings. The filter can also cause divergence (or convergence) if the sides aren't perfectly parallel and flat.

watching from Germany. Keep up the good videos !!

as a hard SF nerd, allow me to give a few tips to reduce a laser beam divergence (this is purely because it's interesting, and not meant to be practical ^^) 1 - use good correction optics. 2 - increase the size of the aperture (the output lens or mirror) of the laser. (that's why military laser always have telescope-like aperture) 3 - the shorter the wavelength, the better. (in atmosphere you can't really go past soft UV as the atmosphere absorbs shorter wavelengths, but if you are in space feel free to use hard X-rays if you can find a laser and optics able to deal with it ^^)

"won't melt when I test stronger lasers" styropyro would like to have a word with you

Interesting to see how much your Hercules diverges, I am betting you could easily get a better dot with adjusting the focus. DPSS lasers tend to have really low divergence overall. It's a huge reason I got into messing around with DPSS, that and such pretty and magical crystals inside. Nice video as always!

Wow, I have never been so early to a Brainiac video, thank you!

I wonder if one of the old helium-neon gas lasers would be better?

I am always impressed by your model car collection when I see it, you should give us a tour. :)

I'd be interested to know how divergent a laser scanners beam is. We have a Trimble unit that can measure up to 340 metres, but as it's not using visible light, it'd be hard to know.

That integral will give me nightmares.

I think you might be misjudging the 1/e^2 point. Weber-Fechner law says human brightness perception is logarithmic compared to the actual brightness.

Great video👍

Nice video . I really appreciate your hard work. 👍👍👍👍👍👍👍

4:04 heyyy! don't underestimate windows calculator 😄 especially the latest version that came with Windows 10 is great.

I don't know whether or not you have everything necessary for this kind of test, but another thing to look at would be how they diverge in a vacuum. For high power lasers that run hot, the air in the path of the beam may get heated up and cause a blooming effect. Plus, higher wavelength lasers diffract in air more

Thank you for the video!

The keychain laser is extra impressive considering that it's red- doesn't the minimum divergence Increase with wavelength?

You should try a long tube laser for better divergence

Are those ringing marks (from the waves interfering with each other) at the far point?

So, a 1 mrad divergence laser will be about 11% the size of the moon when it gets there?

My cats would have gone crazy during that experiment. :D

The laser measure adds it's own length so you can, for example, hold it against a wall and measure the distance to the opposing wall

Our Faro S150 Laser Scanner is 0.3mrad full beam with a beam diameter of 2.12mm at exit.

For a laser used as a pointer in presentations, having some divergence might be desired so that the dot in the target maintains a constant apparent size regardless of distance. I'm just not sure how much divergence would do that. Maybe it isn't much at all.

TIL that the cheapy 200mw green laser I bought (that I always thought was more powerful than 200 mW because it's really bright) that I spent weeks getting a very columated beam on, swapping lens and filters and all that, is insanely columated at .72 mrad

Is it possible to use a small parabolic reflector to improve beam quality?

MS calculator (or any other PC calculator) is so much easier to use with a numpad than with a mouse. Even the standard number keys + operation keys are so much faster. If you do use the numpad, make sure to enable num lock before hand.

Er det muligt at få laser pære som man kan købe til bil, og så tilføje et filter så den kan lyse mere som en normal lytte? Fordi de lyser maget langt, men det er ikke rigtigt bruges når det er sådan at lille pånt.

Should have included a traditional non-diode laser, which is a crystal with a mirror and semitransparent mirror surface where the photons bounce back and forth inside to create a coherent beam via the actual L.A.S.E.R. mechanism.

Hey there, you seem to have resources for something a little more serious and important. How about you built a Michelson Morley Interferometer and rotate it VERTICALLY, that would be awesome, and you get to prove some of that Aether you've mentioned in the beginning

Heh not surprised the cheapo key chain was the lowest since was almost certainly a single mode diode. I have lasers that range from super tight to comically wide divergences. If you have an HeNe you should check it. If it's TEM0 it'll probably have a tight divergence. Or at least I seem to remember it being that way. I could be way wrong. Too bad I don't have a place to set up my big HeNe tube and my argon laser right now or I'd try it out.

I want you to make a video about your scale model car collection.

you can easily simplify the calculation. taking the example of the last laser: 2mm at the start, 28mm at 11.9 meters 28-2 = 26 26 ÷ 11.9 = 2.18 😉

The ones that have a focal point before crossing and spreading again... Isn't that a negative divergence from the actual source?

the shutters from 8:40 laser could use some recalibration, or the mirrors for directing multiples sum of lasers, did you drop it or something?

Why were the diffraction rings formed at the spot at higher distance for the first laser?

9:46 Skip the "quick message" (9:17 is where it starts)

Wait, this is not the test for divergence that they taught in Calculus class! What's going on here? Have I been bamboozled? :D

My favourite videos are the eye annhilationator videos

Hey guys - what difference does divergence make to the width of the laser after it is expanded through a simple lens or mirror? If the divergence is 2 mRad for one laser and 4 mRad for another, will their spot size after expansion differ?

I love Your videos!

If there is a chance you could explain what is happening with near field and far field divergence, it'd be really nice. I can't seem to wrap my head around that.

i love this channel. can you explain a bit about microwaves. i think it will be perfect for this channel

0:45 first word that I see; ASMR xD haha :p

Thanks for sharing this amazing video. Science is so amazing 😃❤️

01:59 - those are some mean subwoofers bro!

Nice

Super fed video 😉 igen igen.. Men når du skriver/siger ud i det uendelige vil det så sige at laser som vi kender dem idag er en lyskilde der lyser uendelige langt og kan kun stoppes ved at en bryder "strålen" ???

Wait, so a milliradian is not a millionth of a Radian, like one would expect, but is in fact a defined metric unit exactly equal to the definition at 1:10? Or is the 1mm/1m divergence just approximately equal to an actual milli-Radian, or 10*-6 Rads, as an actual angle? Thank you!

Happy

Let’s dive into juicy science!

How feasible is it to just sticka lense in front of it and achieve zero divergence? Like obviously not since the manufacturers likely wouldve dont that already especially on the expensive laser, but why not?

im just going to assume that the price/quality of the laser will have a big impact

Is there a 13.5% ND filter that you could use to obtain a reference brightness with a camera with manual exposure and aperture settings, by locking the settings such that the ND-filtered beam is barely clipping at the brightest spot, and then checking how big the clipped patch is when you take a photo without the filter with the same settings?

INFINITE BRIGHTNESS

Hmm... your audio system looks interesting

Would it be possible to use retroreflectors or geometric mirrors inside the laser housing to make the divergence near 0 mrad? Or is that what is already happening and its the quality of the mirrors that determines the divergence?

So much MATH

You should have used mirrors- by counting the amount of bounced you could easily multiply the distance.

Ily

OH YES...

over 2 milliradians of divergence, that's disappointing for a CNI module (the Hercules). I've always been told they were some of the best in the way of beam specs.

Keychain probably has a lot of infra-red

I kinda wanna figure out how good my 50mw Astronomy Laser is. On misty nights I can focus it to a point where it ends up terminating as a bright dot in the night sky.

Dang!!! Do you have a large enough subwoofer setup???? I bet that baby really bumps!...........

What about in a vacuum

If we shape the wave guide in a way that it program photon to spiral in in a proportionally to distance so it never diverse hopefully by shape wave guide wall with screwed like wall that spin or spiral outer photon keep spiral inward prevent divergent. Program light and hologram is the future of uploading soul into forever life in light

7:27 so you like ASMR?

It depends on the quality of the laser, no?

Wait, should not you measure laser spot in a vacuum ? Why you shouldn't if it's interfere with gases in atmosphere ?

Have you tried measuring divergence of your laser measure?

But we never got to see how the youtube button on the Bosch instrument works.

So is it bad that the expensive lasers have high divergence then a cheap red dot laser? Or is it because the powerful a Lazer is the more it divergences?

Knowing the mrad could you make (buy) a lens to correct the divergence to parallel?