# Calculating Energy of a Laser



## Variant (Feb 18, 2006)

I seem to remember from an academic class long, long ago, that lasers of a shorter wavelength have more "energy" than those of a longer wavelength.

Is there a formula to calculate the energy of a laser? (Given its wavelength and power in mW?)

Also, in real life experience, would that mean that mean if you had three different lasers of the same power (200mW red, green, and IR), the green laser would burn through electrical tape faster than a red laser, and the red laser would burn through electrical tape faster than the IR laser?


----------



## Chucula (Feb 18, 2006)

well if you know how many mW are being used, i would guess you could just multiply by time (watt=energy/time) and get the energy of the laser. 

reguarding the different wavelengths, i dont know. good question 
my guess is that less radiation is made


----------



## lorddoomicus (Feb 18, 2006)

Variant said:


> Is there a formula to calculate the energy of a laser? (Given its wavelength and power in mW?)



If memory servers, the energy of a single photon is 

Planks Constant * Speed of light 
------------------------------------
Wavelenghth

To get the power of a laser beam, you'd have to know how many photons you get per second. I would think it would be something like

Energy of one photon * numer of photons /sec
-----------------------------------------------------
time(s)

But I'm not 100% sure about that one. I'll have to research it a bit ...


----------



## dr_lava (Feb 18, 2006)

You are almost corrent, variant. the shorter wavelengths have more energy _per photon_ than longer wavelengths. assuming a 100% efficient crystal, a 1mW IR beam of 1064 nM with (for example) 1 duodecilion photons/sec would enter, and atoms in the crystal would absorb photons (packets of wave energy, really) in a one, two manner. Once two IR photons were absorbed, a single photon with 532 nM would radiate from the atom along with a 1mW beam containing 0.5 duodecillion photons/sec.

at least that's the way I understand it. as far as burning power, it would really depend on the maximum absorption wavelength of the sample. assuming constant, 1mW is 1mW no matter what color.


----------



## comozo (Feb 18, 2006)

If you really want an answer you should post this question at Google's Group alt.lasers, that's were really smart laser people hang out.

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&group=alt.lasers


----------

