Laser thermometer

Hi to all!
Anyone known how the laser thermometers work?
How they can discover the temperature of a surface? By the reflection of the light?



Gregorio

Do you mean the thermophile lpm heads?

They absorb all the laser light, and then compute the power by measuring how quickly the temperature rises... That´s what I think.

ArRaY

ArRaY said:

Do you mean the thermophile lpm heads?

They absorb all the laser light, and then compute the power by measuring how quickly the temperature rises... That´s what I think.

ArRaY

Click to expand...

But then the laser light has to be reflected back to the thermometer... Right?

You mean a infrared thermometer correct? I think that Array is talking about a laser power meter.
Here is how an infrared thermometer, I hope that's what you mean http://en.wikipedia.org/wiki/Infrared_thermometer

spensa said:

You mean a infrared thermometer correct?  I think that Array is talking about a laser power meter.
Here is how an infrared thermometer, I hope that's what you mean http://en.wikipedia.org/wiki/Infrared_thermometer

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I don't mean the laser power meter, I know how they work
But I have seen a pic where a man shine a red laser dot of a thermometer on a surface, and the thermometer write the temp. But thanks for the link of Wiki

Yeah I think that is an infrared thermometers many have laser aiming. (see previous link for how it works)

i need to buy one of these. anyone wanna sell me one? for under 30? lol

pm me if you do

Get one on Deal Extreme (okay, it's$ 32, not < $30).

The laser on "laser thermometers" (actually IR thermometers) are just for pointing, the actual mechanism for measuring the temp is an infrared sensor.

It measures infrared given off by an object, determining the temperature.

EDIT: Here, I found an article on wikipedia describing how they work:

http://en.wikipedia.org/wiki/Infrared_thermometer

EDIT AGAIN: I should read the post all the way through before I post... Someone beat me to the answer ;D

There is such thing as reading temperature using lasers, but it's a heck of a lot more complicated. A recent Ph.D grad at my university did his dissertation on the subject. Basically, they wanted a way to measure the temperature of the actual pieces of metal, at exact places, inside of a running jet engine, aka measure the temperature at exact places along each turbine blade while the engine is running. You can imagine using an IR sensor to look into the temperature of a jet engine isn't exactly practical, and you can never hit exact spots that well. You get heat coming from the gases as well, but you want to see the temperature actually being experienced at the surface of the turbine blade itself. (Since turbines these days run at temperatures where the surface is hotter than the melting point of the metal in the middle of the blade, it's nice to know just how close to melting the whole thing you really are. But that's another whole conversation about the awesomeness of materials science and growing single-crystal nickel super alloy turbine blades and thermal barrier coatings to run them at higher-than-melting-temperature.)

So they dope the thermal barrier coating, or even put another coating on the thermal barrier coating with the dopant, on the turbine components. The dopant is one that is specifically chosen such that it will fluoresce under laser radiation from a powerful laser. The dopant is also specfically chosen based on how it fluoresces. The basic idea is that the laser light knocks electrons bound to the dopant atoms up an energy level, but those electrons have different possible paths back to ground, just like all electrons that are kicked up in energy. The dopant atoms are chosen such there is a spontaneous light emission path to ground, and a non-radiative path back to ground, and that the rate for each of these depends on temperature.

So basically, within the proper temperature regime (depending on the dopant), the rates for the 2 different paths to ground will change dependent upon the temperature. The fluoresce rate won't change, but since the non-radiative recombination rate will change, the number of electrons that take that path instead of the fluorescence path will change, thereby changing the intensity of emitted light depending on the temperature. So you hook up a spectrometer to look at the light coming out, and you can correlate the intensity of fluorescence-based light emission to the temperature at the exact spot that the laser hit based on previously-established correlation ratios, ratios that you get by testing in a less-harsh environment like an oven, or by calculating rate equations for the different paths to ground.

Pulse the laser at the appropriate rate, and you hit the same spot on each and every blade of the turbine and have the temperature on each one, and you can do the same at different distances from the center of the turbine. Knowing the real temperatures at each point, you know the real limits of what you can and can't do in turbine design and operation based on the available materials.

So you CAN use laser light to measure temperature, but it's not trivial, and not really worth it except in extreme circumstances.

pullbangdead said:

There is such thing as reading temperature using lasers...

Click to expand...

Wow it's so complicated, but is very beautiful "thermometer" for the jet engines.
Is true. All is possible with the laser light... LOL