How Hot Is It

[Randy Walker]

How Hot Is It

The question came up in a recent conversation about lasers and I could not answer it. How hot is the beam of a 30 watt laser? And how hot do they get. How much hotter is a 60, or 100 watt laser? This is actually a question posed by one of my customers, and I like to have answers for questions like this. Not knowing seems as though I don’t know my business.

Randy Walker

[Michael Hunter]

I don't know either and I suspect that the beam itself does not have a "temperature" of its own, as the lens and mirrors don't get noticably hot.
It is the beam hitting something else that causes the temperature to rise and that is probably different according to what is being hit - how much energy is reflected back, or conducted away inside the material.

I do know that I can melt the clay in clay tiles with my 60W Epilog - melting of red clay starts at about 2280F (1250C).

[Martin Boekers]

I tell them REALLY HOT! :D

[Rodne Gold]

Thing is - the beam has no heat at all - basically the laser dumps energy contained in the excited photon stream into the object it "strikes" and this heats up. Obviously if a laser is capable of vaporising steel it has the capability of heating beyond the melting pt of steel so it has to heat to nearly 6k degress to get the steel to gaseous state

[Mark Winlund]

The difference between a 30 watt laser and a 100 watt laser is most likely the energy density in the beam. It is like a magnifying glass and sunlight. The energy is concentrated in one small spot, rather than spread out. Energy is not "hot". Something that absorbs energy gets hot. The engraving laser dumps enough energy into a tiny spot to cause the material to vaporize. The material cannot conduct the heat in itself away fast enough, so it vaporizes. This is why you cannot engrave aluminum wirh a small laser. A larger (greater energy density) laser can cut steel and many metals more than an inch thick.

Mark

[James E Baker]

It's really a case of power density that's doing the work. How much energy can we concentrate in a tiny spot. It's that energy that heats up the item being LASERed.

The 2.0" focal length lens in my VLS4.60 produces a spot size of 0.005” (0.127mm) in diameter. With a 50W LASER, this works out to a power density of just under 4kW/sq mm. Compare this with sunlight which generally has an accepted maximum power density of around about 1.4kW per sq metre or about 1.4mW per sq mm.

[Niklas Bjornestal]

this works out to a power density of just under 4kW/sq mm. Compare this with sunlight which generally has an accepted maximum power density of around about 1.4kW per sq metre or about 1.4mW per sq mm.
So about 3 miljon times hotter then the sun ;)

[Gary Hair]

Compare this with sunlight which generally has an accepted maximum power density of around about 1.4kW per sq metre or about 1.4mW per sq mm.

English translation - "it's really friggen hot"

[James Terry]

So about 3 miljon times hotter then the sun ;)

no! only hotter than the sun hitting the earth's surface.

Thanks for the math James. It is a good model for explanation.

Now to the real question, why dont we use lasers to light up solar panels to make lots of energy? hahahah

[James E Baker]

Thanks for the math James. It is a good model for explanation.
No worries. 14 years as a technical instructor does that to you. I'd already done the math a few months ago when someone on another forum was asking about the 1W hand held LASERs from "Wicked Lasers".

[Adam Orton]

There is a small hole in the ceiling above my laser so when people ask me how hot it is I point to the hole and tell them I was trying to etch a mirror, it reflected and went though my ceiling AND roof.. I usually get a wow..

[Dan Hintz]

There is a small hole in the ceiling above my laser so when people ask me how hot it is I point to the hole and tell them I was trying to etch a mirror, it reflected and went though my ceiling AND roof.. I usually get a wow..
:D Ha ha... good one ;):p