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What is the temperature of a laser beam ?

Bionic-Badger

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At that wavelength, the blackbody temperature is 6800K. Otherwise, if you're thinking about the kind of heat you can "feel", that would be more like far infrared energy, so that depends on how well the surface absorbs blue light, and "converts" that into IR.
 





Bluefan

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Cyparagon said:
Not enough information is provided. That arrow is a lot more complex than you think it is. It depends on too many other factors to devise a formula that fits all systems.

You begin to realize how ridiculous it is when you carry the implications to other systems :) :

Kerosine has chemical energy. Chemical energy --> heat energy. What is kerosene's temperature?
A projectile has kinetic energy. Kinetic energy --> heat energy. What is a projectile's temperature?
An object on top of a ramp has potential energy. Potential energy --> heat energy. What is this object's temperature?
Click to expand...
To add: the top of mount everest should be VERY hot if this were to be true :)
 
Cyparagon

Cyparagon

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Bionic-Badger said:
Sounds like one of those Moon landing conspiracy theories. ;)
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2012-02-03-0f4c54b.png
 
scopeguy20

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I will agree w/ Bionic-Badger, as when they talk temp. of a laser color, it is the star temp corollary which is being discussed... ;) -GH
 
Cyparagon

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Black-body temps are never monochromatic. How can you correlate a violet laser with with a blackbody when there is no black-body in which the spectrum appears violet? The same applies to indigo and green.

colorchart.jpg
 
scopeguy20

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While that is true, some stars will look like they do indeed look violet, blue or even greenish, perhaps partially by contrasting with those near it. ;) -GH
 
R

Roam

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brendon7358 said:
What is the temperature of the photons coming out of a 1W 445nm ? Does anyone know? Or is that just not how it works :thinking: :thanks:
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Temperature is a macroscopic and statistical quantity. It doesn't apply to elementary particles like photons or electrons.

Btw, blackbody radiation will heat up a thermometer but not up to the temperature of the blackbody itself. The temperature associated with a certain wavelength of light simply is the temperature of the blackbody that emitts a spectrum that peaks at that particular wavelength. You can't say the monochromatic laser light has the same temperature as a blackbody spectrum of radiation that peaks at that wavelength.

You need a spectrometer to measure the temprature of the blackbody itself, not a thermometer.
 
Benm

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Roam said:
Btw, blackbody radiation will heat up a thermometer but not up to the temperature of the blackbody itself.
Click to expand...

It actually will, as long as the thermometer itself is also a blackbody (or modelled as such). If you put 2 blackbodies in a box with (full spectrum) mirrored walls, they eventually must become the same temperature to reach maximum entropy in that system.

The IR thermometer works by looking at the thermal emission spectrum, which has a very specific distribution. By measuring the ratios between 2 or 3 IR wavelengths, the temperature is calculated accurately within certain limits.

If the measured object is not a blackbody in the ir range used, an ir thermometer will produce an incorrect reading.
 
R

Roam

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My point was when you shine a laser on a thermometer the reading you find is the temperature of the mercury as it keeps absorbing the energy of the photons transferred to it, it's not the laser's temperature.

Yes, that's only true if you put them in a closed isolated system so as they can exchange energy until settling into thermodynamic equilibrium. In most normal situations bb radiation will not heat the target to the temperature of the bb itself, luckily for us earth dwellers.
 
Smeerworst

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I saw someone trying it on a digital thermometer on youtube....
First i was like :thinking: :crackup:

But it did read it.
It went to 109F and then it stopped couse the digital thermometer couldn't read more.
He shined it at the metal part....

Cheers, sm
 
Hiemal

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Smeerworst said:
I saw someone trying it on a digital thermometer on youtube....
First i was like :thinking: :crackup:

But it did read it.
It went to 109F and then it stopped couse the digital thermometer couldn't read more.
He shined it at the metal part....

Cheers, sm
Click to expand...

He sounds like a bright individual (pun intended) :crackup:
 
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