Laser sensitive coating / paint

[spidennis]

I'm looking for a coating or spray paint that is sensitive to a specific laser color.

I'd like to use a two color laser projector, one color for placement onto the target area and then I can spray the sensitive paint into that area, then once fully coated, then turn on the etching laser to see the pattern in daylight.

basically this is almost like black and white photography in a darkroom but using a laser instead.

I've seen uv paints but this must be used and seen in bright outdoors daylight conditions.

Is there such a material? Lasers are used to burn thru materials, it should be able to photo etch something right?

 

[DrSid]

Burning paint away is easy. My 445nm 1.5W can do that. Burning just one layer might be tricky. By burning one layer, the heat will for sure penetrate into next layer. Only top layer counts, and then it's all about heat transfer.
But you could always use paint on metal, then burn away the paint, exposing the metal .. voila, the pattern is visible. I was trying to measure power of my lasers by measuring temperature of blackened aluminum foil .. and with my 1.5W laser it worked just like this. I used simply several layers of black marker to paint it.

 

[spidennis]

Dr.Sid,
that's interesting! ok, more details ....
I'm a sand sculptor and have to carve complicated logos,
I start out with a wall/block of sand ......
now comes what I envison:
place the tripod with laser projector in front of the block of sand,
turn on the "ranging laser" and position it correctly.
then spray the areas of the image that the laser paints to.
now turn on the "developer" laser and mark the pattern.
I'd like this to not be dangerous because there's usually other people around.
All of this must be able to be done in bright outdoor daylight.
Complicated logos can be tricky and time consuming , this would make it much faster!

 

[DrSid]

Well .. burning paint from sand sounds easy. But ..
Doing it over variable distance would need a lot more complex setup and more power. 1.5W can burn thin layer of paint, but it would be from few inches, and it would be focused to the specific distance. Burning power (power density) decreases with distance.
Doing it at daylight would be no problem at all. But being safe it would not be. Any power capable to burn paint would be dangerous even to skin .. not to say eyes. Industrial burning lasers always have casing which prevents the beam to leave the machine. Burning into a object under open skies would most probably be dangerous, and also illegal.

 

[spidennis]

Yeah, burning might be a bad thing ......
and that's why I was thinking of photography based ideas,
a photosensitive material that would "develop" when a certain color laser would hit it.
I'm wanting to use a projector that could be used 30' away if need be.

 

[DrSid]

Yes .. I see the reasons now .. on the other hand I don't know a solution. There for sure is no 'laser sensitive' paint. Paint could be sensitive to specific wavelength .. but sunlight includes most wavelengths which we can create laser for. Using stencil and spray would be simpler. And hey .. you can cut the stencil with laser. Actually most stencil companies would do just that.
Also you could use laser projector to project shapes on the sand .. but it would look mild at best with full sunlight. It would look great at evening/night though.

 

[spidennis]

You got a point about the sun's wave lengths ..... hummmmm........ and I've done the stencil thing and use it when I have to, but that is slow to prepare and it's only one size, I am wanting something 21st century, maybe back to burning then? and just be careful? how about 20'?
and a laser light show on sculpture at night would be cool ...... of course real fire looks great too!

 

[DrSid]

Well .. 21st century means we have dangerous burning lasers .. just not safe burning ones :umbrella:

As for the distance .. laser cutting machines work with constant 'target' distance. The laser head moves in two direction above the plate of material cut. Basically like huge plotter. Problem is it the table has some maximum size, and because of housing its pretty big and heavy. Non transportable.

As for the burning .. the size of the laser spot depends on the distance .. so if you can cut at 2 inches, at 4 inches the dot will have twice the diameter and 1/4 of the power density. That can be however overcame by using larger laser aperture .. for example that anti-missile airborne laser I have in my avatar has 2m output mirror just for that reason. You would not need 2m, let's say 10cm or so might cut it.

Theoretically there could be laser with swiveling head .. which would rotate to hit different areas. But then it would have to focus in realtime. It could be rather small .. let's say size of 10cm astronomic telescope. Some of them actually have swiveling motorized mount.

Still there is a problem with safety. Safe (and legal to shine outside) is 5mW. We are talking about at least 1W .. ie. 200 times more. Cutting tables have tens of watt up to hundreds, if they cut metal .. but as I said, those are enclosed machines. Not only direct hit by the beam would be dangerous (even to skin), but also just watching the spot would require protective goggles .. for all around.

I think it is possible .. I even think such lasers already exist .. but so far it's military grade technology.

 

[spidennis]

with all that it burnt my brain so it's back to photo sensitive ideas!

When the photo resist, think circuit boards, it sprayed onto the sand wall surface it would have a limited time before it becomes developed by the sun, the laser would be a much higher level and do it much quicker, and so I'd have a pattern to go by for at least a little while, and long enough to scratch into the sand whatever pattern was left.

now such a material may or may not exist in such a form but I'd think that by now just by accident that someone might have found a material that would react in this manor?

with so many laser types now available I'd think something would work?

Once I found this material I could make my own paint, and airbrush it.

with this route then I could use the laser projector and basically use any .jpg file for projection. I could even receive the logo at the job site and doctor it on my laptop if it needed fine tuning for laser projection.

I guess we need to know if anyone has come across a problem where the laser is marking up something? and I need to look into photo sensitive materials ......

 

[DrSid]

Laser projectors usually use vector graphics. And even then .. as you distribute power of the laser over large area .. it's not that powerful any more (that's why laser shows are not setting things on fire). In other words .. common laser projector wont do that much difference against daylight .. much less sunlight. What about making the exposure at night ?

Interestingly among all the experts, there is just two of us chatting here ..

 

[spidennis]

I already do the night thing with my 1954 Argus Slide Projector. I print with my HP 5mp laser printer (black toner) onto a clear plastic (laser) sheet so it fits to a 35mm slide, and I usually fill up the sheet with all kinds of different images, then print, cut, mount and project. But this only works at night, and becomes a limiting factor. With indoor work I can sometimes get the lights turned down, when I get lucky.

I had a friend that just recently need to make an 8 foot sign and it had a big osprey bird on it and she was going to hand draw it until I suggested using my projector. They had a large garage to work in so the projector could be set back far enough. it worked great, but they were able to work in the dark garage .

 

[spidennis]

Interestingly among all the experts, there is just two of us chatting here ..

maybe they are all out there experimenting with all their various wave length lasers on all known materials? It could be an interesting thing to set out to do? Or at least notice for, so when it happens it's a happy accident!

oh, I also use the 1954 Argus Projector to cut out stencils when I have a daylight job, it's a lot of hand cutting! I spray paint the stencil then carve the sand ..... it produces an accurate logo ..... a lot of prep work though!

 

[spidennis]

this is an interesting idea
Sun Painting (with Setacolor) Instructions
It's very much along the lines I'm looking for!
Instead of the sun could the a laser do this?
I'm not looking for a full blown photo of something,
line art is what I'm after, so it's used as a guide ....
kinda like a coloring book!

 

[spidennis]

based along the same ideas as above
Inkodye develops photos on T-shirts using sunlight
If the properties could be tweaked a bit, maybe make it less sensitive, then I could get a longer working time?


Lasers could get a new real world application if this were to work.

 

[DrSid]

Interesting .. question is what wavelengths it would react to. That would need testing.

 

[spidennis]

https://www.matsui-color.com/thermolock/
I'm thinking something out there is gonna work ....
here's another contender.