Bad Beams? | How divergent are lasers?

Laser beams are amazing to watch since they appear like a string of light. Not like a wash of illumination from other light sources.
But does a laser beam spread out? Does it diverge - getting wider over distance? Let's measure the divergence of my cheapest and most expensive lasers!
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See the correction optics in the 2W version here: • LaserCube 2.0 | They D...
Measuring power and wavelength of my strongest lasers, including the Laserglow Hercules: • Strongest LASERs in my...
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#Divergence #Laser #Brainiac75

[@cringemaki]

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

[@explodingtoast9898]

Lol

[@AJMansfield1]

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.

[@postvideo97]

Yes, the inverse tangent is linear at very small values.

[@Hvidbergen]

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!

[@mduckernz]

Can you give a brief description of the generative phenomenon? Micro scale destructive interference within the cavity (no idea if this is a thing, just the first thing my intuition spat out given the pattern...) ?

[@Hvidbergen]

@@mduckernz In the case shows at 3:00, it is the roughness of the surface that gives rise to speckles. It has to be a surface that reflects diffusively for it to happen, which the computer case does.

[@CnCDune]

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

[@muffty1337]

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

[@hugoknapp]

Me too!

[@DiDe273]

Basshead 🤙

[@Cyparagon]

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.

[@twjackson94]

someone that know physics on youtube.

[@yurym4385]

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.

[@albyboy4278]

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.

[@MrAlpacabreeder]

Not really. Even perfection will still diverge due to the diffraction at the edges of the beam. NASA lasers bouncing off the Apollo reflectors are several miles in diameter by the time they reach the moon. This can not be improved on no matter how good the collimation is, it’s physics.

[@sherrymaloner8843]

You uploading today was the highlight of my day

[@1kreature]

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.

[@universum-theuniverseexpla6565]

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.

[@UncleKennysPlace]

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

[@realvanman1]

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.

[@chuglyc]

Gotta love how the cheap laser has the best divergence

[@ccllvn]

watching from Germany. Keep up the good videos !!

[@glasslinger]

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

[@Jesus_paid_it_all]

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

[@brainiac75]

Always try to make it on a Friday. Gives me the weekend to focus on the next video x) Much more to come!

[@jokubasvanagas3174]

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

[@ronsku57]

Same

[@brainiac75]

Very early indeed, Jokūbas! Thanks for the fast watch :D

[@izzieb]

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.

[@brainiac75]

It's probably an IR laser, so you could use an IR detector card to make the spot visible. If it can scan at good resolution up to 340 meters away it must have pretty good divergence. Would be interesting to test, if they don't specify the laser's divergence. Thanks for watching!

[@izzieb]

@@brainiac75 From what I can find, it's about 0.177 mrad. Thank you for making your great videos!

[@brainiac75]

Wow, that's not pretty good. That's very good divergence! But again, it is needed if working at 340 meters distance. Thanks for the info.

[@pizzablender]

@@brainiac75 Why not just use a camera to "look" at the beam?

[@The.Heart.Unceasing]

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 ^^)

[@antongolovko1149]

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

[@AngDavies]

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

[@inductivelycoupledplasma6207]

Yes, although it's a low power diode operating in single mode. Higher power (especially blue) LDs operate in multimode, and thus have lower beam specs and higher divergence!

[@DEtchells]

Huh, I was thinking that divergence would be inversely proportional to wavelength, kind of like diffraction…

[@snowthemegaabsol6819]

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

[@drozcan]

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

[@brainiac75]

Hehe, I actually do use it a lot when making calculations for my videos. Thanks for watching!

[@TheBackyardChemist]

Nah, the windows 7 one was way better for serious calculations, you could click into and edit the expressions in the history

[@drozcan]

@@TheBackyardChemist You now can too. Also it's just a port from windows 7 version to Windows 10 WPF

[@TheBackyardChemist]

@@drozcan I wouldnt know, I actually hacked the win7 calculator into win10, but thanks for the tip

[@dinitroacetylen]

(laughs in Speedcrunch)

[@54321eclipse12345]

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.

[@TriPham-j3b]

Air pressure resulted in x axis more diverge than y axis. Just like submarine presure change depending on ocean floor

[@mykulpierce]

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

[@prostaknaivnyj5976]

too bulky even if small, frensel lens works much better

[@pauljs75]

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

[@LegendSpecialist]

Great video👍

[@bright_lego]

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.

[@brainiac75]

Totally agree, but for viewers wanting to replicate the calculations in one go, it is much easier to follow along when I use the mouse ;) Thanks for watching!

[@bright_lego]

@@brainiac75 Or you could do what I just do and use an (i)python shell as a calculator. It may not be as easy, but it is much more powerful than a traditional calculator.

[@simeon136]

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

[@TriPham-j3b]

Thanks!

[@brainiac75]

Glad you like it, TriPham :) And thanks for the generous donation!

[@syedchennai16]

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

[@Apti-Erhan]

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?

[@JoshuaNicoll]

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

[@randomelectronicsanddispla1765]

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.

[@genshineditsjoon]

Thank you for the video!

[@brainiac75]

Thanks for the fast watch ;)

[@Chris_50bmg]

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 😉

[@barstiryaki4441]

Thats true When x is really small, tan(x) aproaches x So arctan can be ignored because x is on the order of 0.001

[@jatigre1]

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

[@TriPham-j3b]

Could longer ruby help keep laser focus better

[@MathIguess]

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

[@LtKernelPanic]

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.

[@duanecjohnson]

You are correct. HeNe lasers have far lower beam divergence. I have several models. One is about 12" between the mirrors and produces a spot of about 1" at 1 mile distance. Basically the beam divergence is defined by the number of wavelengths between the laser cavity reflectors. In simple diode lasers this is a few mm or so. redrok

[@rafakordaczek3275]

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

[@aleksanderkysiak9540]

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

[@bassmikdk8360]

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.

[@29Aios]

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

[@lachlanlau]

Keychain probably has a lot of infra-red

[@ambrosekillpack4841]

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.

[@Soandnb]

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.

[@dhilipraja]

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?

[@brainiac75]

In theory, there's no link between the power and divergence of a laser. But in practice, strong diode lasers tend to have multiple emitters. They need more high-precision, expensive correction optics to get good divergence. The difference in divergence between the keychain laser and the expensive Hercules is mostly due to totally different lasering techniques. The 532 nm green is much more complicated to achieve than the 650 nm red. Thanks for watching!

[@ZeroMass]

@@brainiac75 Divergence increases with output. Adjust the output of the diode through it's power supply and measure.

[@tiagotiagot]

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?

[@Midaspl]

3:04 Why would you write it as definite integral from - infinity to +infinity, lol? It's basically the same as indefinite integral.

[@000bHd000]

dont think those are the same

[@universum-theuniverseexpla6565]

actually you are incorrect, a infinite integral does not measure antiderivatives of a certain function of x, however a indefinite integral, just because it measures antiderivatives does not mean it is a infinite integral, unless you define that in the parametrization or in the number to approach at the top of the integral, and also he was trying to find the derivative value not the antiderivative function.

[@Kholanee]

My favourite videos are the eye annhilationator videos

[@brainiac75]

More laser videos to come ;) Thanks for watching!

[@zenvir1680]

Hmm... your audio system looks interesting

[@ewozniak5228]

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

[@bgezal]

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

[@Sofia-qn6fs]

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

[@brainiac75]

You're welcome, Sofia. Science is indeed in every amazing thing ;) Thanks for the fast watch!

[@Cdrsan]

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?

[@EUClasses03]

Nice

[@ericpham3751]

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

[@rethinkscience8454]

What about in a vacuum

[@RedFenceAnime]

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

[@dozog]

No

[@Paxmax]

Haha, you didn't measure the range finder! =o) Might be the best of the bunch? My range finder Bosch GLM 80 goes from about 5x2mm line to about 12mm diffuse roundish shape in 8,6m.

[@Pathfinder_A79]

So much MATH

[@OpreanMircea]

But WHY? why does the cheap red laser have a better beam collimation than all the other lasers you have

[@twjackson94]

maybe because it doesnt have a lens in front of the diode

[@WormasCZ]

Have you tried measuring divergence of your laser measure?

[@dolamskudoiski306]

INFINITE BRIGHTNESS

[@ProfaneGod]

The reason a company donates a product is because it is cheaper than paying for adverts if it is shown and should be classed as a paid promotion in your video because your payment is the product many companies use this underhanded tactic on multiple people making videos.

[@brainiac75]

Agree that it is paid promotion, and I did check the 'paid promotion' in the video upload even though I have never received a cent from them - 'only' the LaserCube. Wouldn't call it underhanded. It is pretty obvious - especially when I disclose it two times in the video ;) Thanks for watching!

[@ProfaneGod]

@@brainiac75 I was not saying you were underhanded i was saying the companies were underhanded

[@TomKappeln]

You could try my 1 Meter Spectra HeNe Laser to messure .... hehehehe

[@alejandroalzatesanchez]

Thicc laser beam

[@jeffczermanski2993]

I'm no 'scientist', but shouldn't you measure them without the lens in front of the laser?

[@mattigator600]

Hi 🙋🏻‍♂️

[@brainiac75]

Hi, mattigator. Thanks for the fast watch!

[@guffaw1711]

double subwoofer wtf

[@DestroManiak]

he sounds sooo cute

[@BillFromTheHill100]

Are you a robot?

[@djsmileyoflasvegas]

👍

[@gabriel_martz1470]

th2% tungsten 30.64%w185 β− 75.1(3) d 185Re

[@brainiac75]

Huh? Sounds like a thoriated welding rod. Watching one of my videos on radioactivity? ;)

[@gabriel_martz1470]

@@brainiac75 yes :)

[@gabriel_martz1470]

@@brainiac75 nuclear transmutation of tungsten into rhenium.

[@88njtrigg88]

Retrograde reflector to the Moon here l come..

[@PlutoTheSynth]

This is probably the first and the last time I’ll ever hear you say you “ghetto”

[@imSomebody-m4c]

hii

[@reastle1307]

'😮🔥

[@leothealien5660]

:)

[@urbannanni5864]

The keychain laser is more accurate because cats are way more discerning than your human standards.

[@JAKOB1977]

have you made links prohibited on your channel? tested my NUBM05, 06, 06, 07, 08 and tried to link to Imgur slideshow of the results? but seems one comment is being deleted by the YT bot, and as a partowner of YT, as a danish shareholder in alphabet inc, though not a lot.. it seems it is YT filter that channel holders can implement' but aint mandatory. If you're the source that removes your viewer's ability to interact and share results... you should really think hard if that is the way you wanna go.. as a fellow Dane, I hope you have a little respect for freedom of speech and the ability to interact on social media and not silence your viewers like this..rotten approach

[@MadScientist267]

So there's at least one cheap thing that comes out of China that's better than... Oh nevermind... I'm gonna just pretend I didn't realize that

[@TonnyCassidy]

The measurements are done in metric, feels bad for american viewers

[@lamuzzo5120]

stopped watching too maths

[@bedbomber3531]

Was i first?

[@maxwag9263]

no you're third

[@bedbomber3531]

@@maxwag9263 ok

[@gravel_slope]

yes u were first

[@brainiac75]

Within the first minute - fast enough for me! Thanks for the fast watch :)

[@gravel_slope]

@@bedbomber3531 my guy u were first hes just shittalking

[@KRISHGAMING21]

First 😎

[@snickerdoodle1057]

Ily

[@Ass_Burgers_Syndrome]

You lost me at "Hi" !!

[@aarongreenfield9038]

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

[@brainiac75]

Hehe, nice touch. I do like to guide with a laser sharp focus x) Thanks for watching!

[@GQuack]

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

[@psygn0sis]

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

[@VeganCheeseburger]

Would love a video on your entertainment system speakers!

[@a.wright281]

Such an amazing video, keep up the good work!

[@brainiac75]

Thanks, Caroline. Much more to come!

[@marc-andreservant201]

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.

[@dustinbrueggemann1875]

shorter wavelengths also make it easier to get a finer beam. Blu-ray stores more information because the blue laser beam is physically much smaller at it's finest diameter and also can be focused with greater accuracy. Those two factors mean that you can fit not only more layers, but also significantly more tracks per layer.

[@somerandomguy001]

7:27 so you like ASMR?

[@NoOne-ef7yu]

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

[@the_undead]

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

[@mezzer34]

I was enjoying the video until you used cm 🤮. m all the way