How to work out power required to generate temprature rise?

[Ellipsis]

Hello. I hope this is the correct place to ask this.
I have a small little project I would like to try to build.
I would use a laser and 2 mirrors (which are to be rotated by motors and set at right angles to each other).
In this way it would be possible to control where the laser light falls to any 2d points.
Ideally I would like to be able to trigger thermal paper or melt black plastic or similar with my laser.
However I am having trouble working out the power that would be required for this. I would obviously like to keep costs to a minimum but also maintain safety. As far as I can tell a common 5mW diode would not be powerful enough to raise the temprature where it hits a noticible amount at all. However would 2 be enough? This could be a nice way to go as it would keep a high level of safety as each laser would still be lower power. Would this work? I would really be quite happy with a temprature rise of even just 1 or 2 degrees celsius (In any amount of time).
If this isn't possible then what laser would be least dangrous (wavelength) and least costly for this kind of experement?

Also I know that it is possible to raise temprature using other methods than lasers. However being able to heat only 1 spot in 2 dimentions and still not cost a huge amount seems to only be possible with lasers?

Thank you.

 

[pschlosser]

The challenges with using X-Y mirrors to direct a beam onto a surface for cutting and etching is that the focal length changes between the middle and the outer edges of the target.

Often, CNC (machining) principles are employed to keep the laser beam stationary, and moving the substrate (in this case, your paper) left and right, up and down using a CNC XYZ table.

White paper reflects light so well, it is not easy to get it to absorb heat energy from low-power laser light. We can overcome this by cranking out a lot of energy, on the order of Watts, onto the target.

If you wanted to burn BLACK paper, you would only need 100-300mW at close range in the visible spectrum. Relatively simpler and safer than working with UV ablation or IR wavelengths. We are blessed with 445nm (blue) laser diodes that can crank out 2000mW or more, for a relatively low cost.

 

[Ellipsis]

Ah, thank you for your quick response.
Yes I thought white things might be infeasible. That's OK. I just wanted to check that there wasn't certain wavelengths that they actually absorbed really well or something. Although would I be right in thinking that an infrared laser is more deadly as it couldn't invoke a blink reaction? Do you think a blue laser would be best for this then? I'm a little disappointed to hear X-Y mirrors wouldn't work. I was under the impression that standard lasers had very little/no spread? (For example if I point my small red cheap laser pointer a long distance away the point it creates it almost the same size as a near by point?). Could 2 lasers focused on the same point overcome this? (By overlapping their points they could limit where got the "double dose"). I know that it is possible to use a stepper motor to move a lense and focus a laser. However I'd rather avoid this if possible as it sounds expensive and also really tricky.

Ideally I'd also be interested in a minimum amount of power that would have this effect. I can always preheat the surface to just below melting anyhow.

 

[robmobz]

Actually a CO2 laser would AFAIK be absorbed well by almost anything but unfortunately they are both large and tend to be in the order of tens of watts.

 

[Ellipsis]

Hehe. Thank you. That's interesting to know. I think maybe it's just so powerful it's at least absorbed a little by everything but still enough to melt it? In my case however it would certainly be overkill. (And costly!)

 

[Ellipsis]

Sorry to double post.
Just wanted to ask if anyone knew of someone else who had made a similar thing in the past? So far I cannot find anyone who has attempted it. Anyway, any ideas/advice would be great.
Thanks.

 

[robmobz]

Sounds to me like it is a laser cutter. Things has a thread about his build somewhere which may be useful to you.