Looking for an IR laser to make a warm spot, one inch across

[G J Beesy]

Hello there! New here. I do special effects for tv commercials, largely for food photography. Here's what I'm trying to accomplish, and believe it or not, this is a real thing, that comes up. Imagine a hamburger commercial. Imagine a closeup of the square of cheese sticking out of the edge of the burger. Now imagine that corner of cheese is now softening, drooping, and melting down the side of the burger, over the meat. That's what I'd like to accomplish, from a foot away, with an IR laser. An invisible spot about an inch across, with enough energy to heat the cheese, just enough to melt- it doesn't have to boil or bubble. This would also be useful in butter melts (imagine a pat of butter on a stack of pancakes, starting to melt and run.)
This can be done with a heater or old fashioned paint stripper, held above the food, but the trouble is, it creates a shadow, and it's too wide- the heat browns the top bun and wilts the lettuce.
Would it be possible or practical to try this with an IR laser, with the beam defocused to a large spot? We're talking about enough heat to slowly melt, not to burn. Something that, if it hit your hand, you could feel it, but it wouldn't cause an immediate burn. I suppose it depends on the specific heat of cheese, which is mostly water and oil. How many watts would we be talking about? Any ideas or insights are appreciated. Thanks! Geoff

 

[julianthedragon]

You would likely need somewhere in the 10s of watts if not stronger. Lasers build heat like a magnifying glass, by focusing light down to a tiny spot. The larger the spot, the greater power needed for an equal heating effect. My 1W 1064nm laser struggles to heat orange objects even when focused to a point, hence my educated guess above. Additionally you have to consider how the IR frequency interacts with the cheese (most likely - the reflective yellow surface won't be optimized to absorb the light). In my imagination you could achieve the desired effect more easily with a violet or blue multi-watt diode array, provided you quickly turn it off before taking the shot.

**Any of this would be highly dangerous to the eyes of anyone in the room, the camera sensor, and risk creating a fire hazard - especially if using IR. Eyes and camera lens would need adequate OD laser-blocking filters**
So, I don't like being a buzzkill but you should keep all your options on the table...literally.

Edit: Admittedly never tried melting cheese with lasers, if anyone is crazy enough to experiment and discredit my guess go ahead

 

[CurtisOliver]

So one of the things I didn’t imagine myself doing this morning was looking up absorption spectrums for cheese. For a laser to transfer energy into heat the photons need to be absorbed. Therefore you need a wavelength that is absorbed well by the cheese.





As you can see from the spectrum above, cheese increases absorption the further into the infrared spectrum you go. 1064nm isn’t going to be effective enough. Er:YAG is likely to be more effective at 2940nm. However this is an extreme way of getting a good shot of cheese dripping.

 

[Encap]

Is important to understand/know/recognize that a laser beam has no temperature - there is no inherent "temperature" to a laser beam. Heat is the random motion of matter particles (atomic or molecular particles).
A laser beam itself is not made of matter but of photons, which have no mass, thus a laser beam can have no temperature.
"Heat" is caused by a laser beams energy being absorbed by a materials surface and turning light energy into heat energy.