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nubm31 focalization
I am trying to obtain a laser able to burn small plants (or very small plants) at a distance of about 0.75M . will be a scanning device to kill weeds.

I found the nubm31 could be interesting but unsure if it can focus enough. I am expecting a dot 1x1mm or at least 2x6mm at 0.75M distance.

Looks like nobody did try to focus at this distance. So I am pretty unsure if it is feasible.

but considering this I suppose it should be possible :

-Junkers wrote it's possible to focus nubm31 a dot 0.6mm with a 60mm lens and a 60mm focus.

-BrilliantLasers shows a picture of the oval dot he obtained at  5m that looks like to be 1x3cm

My question is : what do you think about it ? possible or not ? and how ?   beam expander + focusing lens ?

only focusing lens ? using aspherical convergent lens +2 ?
Great idea!  It should work well!  Congrats!  Big Grin

You don't even need to burn them.  All you need to do is heat them up enough.  Years ago I saw an invention that used steam to kill them.  It was a tractor that drug a thick rubber sheet over the weeds and steam was injected under the rubber sheet to heat them up enough to cause a cellular breakdown.  Being that you don't need to burn them you'd avoid the problem of starting fires.

I don't think any of the laser array options would work very well for your application.  The problem may be that when you're dealing with multiple beams it's probably difficult to get them to all converged into a single powerful beam.  When people are quoting spot sizes I think they are referring to a spot size at a single point along the transmission line of the beam.  Whereas, what you need is to be able to provide the beam energy at any point along the transmission line of the beam because the foliage will be at random heights.

You could probably get away with a 1 or 2 watt laser that is a single beam.

If you're planning on making a product you might want to see if there are any patents that are in force covering this.  There may be being that it is a very good idea, so it may have already been thought of and patented within the last 20 years or so.  If not then file for a provisional patent and secure rights right away!   Big Grin

Oh and, I just remembered, there IS a way to focus a laser spot in 3D space just in case you ended up needing to do that.  Take a look at this.


They're using a varifocal lens to do that.  Probably as expensive as hell for that lens, but I just wanted to show you that is possible.   Smile
Thank you James for your help 

The steam weed killer is very difficult. You need an important amount of energy, maybe as high as 4 liter of fuel to sterilise the earth on the last 4cm layer for 1 square meter. And its heavy machines, very time consuming. And it's not totally weed free.

The best option around is the direct gaz furnace carried over the raw, would fit me, but it's heavy and dangerous (starts fire all around) and you need 50 litres of LPG for 10000 square meter to surface treat.

I have created a robot that can carry such a laser (and patented). Uses only solar power. I don't plan to patent just a scanning laser  Tongue lasers does scan paper in printers and many things from ages already

I don't need an active beam as you think. only a focused beam at about 75cm with an angle and I scan that beam over the plantation bed, scanning all the bed and cutting / burning / heating the stems especially the small young ones, at a state they won't survive because they can't bear that stress.

It's possible a simple 5W nichia diode could do the job but I feel unsure about the scanning speed. Because a field... it's big !

But I want it also to be able to have effect on bigger weeds. Because it happens to have. Don't know what could be the effect for a 90W scan every 1cm for a field that is going to be invaded by weeds. Probably have a partial effect, doesn't mean it's bad.
*high five*  I love robot applications like that!   Big Grin

I also love solar!  One thing that comes to mind in that regard is a non-imaging concentrator, like this,

[Image: 3-s2.0-B9780081003015000059-f05-01-9780081003015.jpg]

With something like that, with say, a one square meter aperture, you could easily develop enough heat to scorch weeds without getting up to kindling temperatures, provided the weeds are not much taller than say, 75 mm.  An advantage of a concentrator like this is it doesn't need to track the sun for most of the midday.  Unless the terrain was hilly that is.  In that case, you would need a heliostat.  Heliostats are easy to make with a couple of photovoltaic cells and some gear-reduced DC motors.  No computer whatsoever!

Lasers on the other hand are cooler!  HAHA! ??  Well, if you can get around burning people's retinas out. ?

Have you seen RC Test Flight's solar rover experiments?  Here's one of the vids he has up on it.

Hello James

it's a fact direct sun is much more efficient than Using photovoltaic. Impossible to open your youtube video. Area problem maybe ? 
machines needs not to exceed the clearance normal agricultural tractor have, managing the sun position + the target and not having huge wideness appears to be a challenge to me.

The system have to be able to work also in winter. A PV system can accumulate enough energy, and later on do a laser work. Or directly to get the battery charged by a network (actually it's just a bigger solar array network)

But sometimes if we could harvest the sun directly maybe using some parabolic, then feed a fiber, makes things easy to handle, then focalise it the same way I intend to use my laser, then yes I would become really interesting.

Don't know if this concatenation of strong light in a fiber is possible. Haven't look for, but if it is, some would already use that to light houses I think.

For the moment I've created the machine, the only tool needed is the laser, the machine can provide the power already so it's the easy way to go... (and still a lot of work)
I fixed the video.  I'm not sure what happened.  I'll have to do some experimenting at some point to find out.

I did see in the early eighties an invention for solar indoor lighting that used fiber optics.  It consisted of a solar concentrator that focused sunlight on the end of a fiberoptic bundle.  The fibers were routed down into an indoor living space and were woven into a sheet to make a light panel.  To get the sunlight out, each fiber in the sheet was deeply cut with a V shape that allowed the sunlight to escape.  The panels were quite bright!

Getting back to lasers.  There are lasers that can turn on and turn off so fast that they can do ablation of things without causing contiguous heating.  Look at how femtosecond lasers are able to micromachine these match heads for example.  Thus, using a laser like that, you could drill billions of microscopic holes in the weeds, and then they'd just dry out and die.  The benefit would be no chance of starting a fire.  What's the drawback?  Super expensive!  Big Grin   Although, there are efforts in place to make chip-based femtosecond lasers that would have a much lower cost so it might be something to keep in mind.
thank you for the video !

mine is as big as a car, 400Kgs and it's full solar too. And it's at real work already. 

if some search for laser destructor robot, now have :

(I don't know how to enbed youtube video here)

they are doing camera scanning and destruction. And this particular one is not solar.

But I'm on much cheaper apparatus, and it's not selective. No camera to search weeds. Just scan with laser everything in the specified area.

The matter with solar light and fiber is not to use it from the fiber, it's to make it enter in the fiber. And especially to enter kW in the fiber. We can input kW of laser into a fiber. Unsure if we would be able to do it with sun.
Patent is one thing, reality can be different. The patent office don't test the thing at all. It has other criteria.

Cut a fiber along is an idea, but only with plastic fiber that certainly don't handle the high power. The hard fibers will probably not let them get cut along like this. Maybe need a lens to focalise the light on a fiber end. But to enter a fiber the beam should be parallel like a laser, so need a kind of reversed telescope lens to obtain the parallel beam but very small.
To embed a video, click here,


And then here,


Your robot rover sounds super cool!  When you get around to posting about it let me know because I'd be interested to see what you've created!   Smile

The robot rover in the video looks overkill but I guess if you have money to burn then why not.  I wonder how well the computer vision system works.  Imagine going out to check your crop one day and it's all burned up?  HAHA!   Tongue

Yeah, I'd like to do some experimenting with fiber optics and solar.  Sounds like it'd be a lot of fun to see what's possible with that.  I'd like to experiment with getting concentrated sunlight into a beam form as well.  How powerful and how concentrated could a solar beam be made?  If I get some time I may look into that in the coming months.
Their diesel autonomous robot is very good solution if it works fine (detection + software without bugs). Launch that in a field with correct configuration and the work is done. Saves from using chemical, very good for our health. Easy to guess this machine could be a pain if does not work as should.

Very probably the future of agriculture is using such robots, and maybe some solar autonomous too.

Well I have not this financial power and I'm alone, so I'm dealing in the small stuff that also works.

Yes it's definitely super cool. now used only as worker carrier not in autonomous robot mode. Ok I will let you know when I communicate on it.

I am also interested for solar into a fiber in case it works !
That's the first thing that came to mind.  Good health!  We wouldn't need Roundup-ready genetically modified organism technology.

I agree!  I think you're definitely seeing the future with those statements!  Especially the AI aspect of it.

Yeah, I'll let you know about whatever results I find with that.

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