Laser - Einstein's Coefficients

[cupid.callin]

Hi all,

I was reading Lasers and i read something like this:

for spontaneous emission, the rate of decay of electrons in high-energy state to low energy state is given by:

$\frac{dN_2}{dt} = P_{21}N_2$

where P₂₁ is equal to the probability of electron to drop from higher energy state to lower energy state.

Now, P₂₁ was defined as $P_{21} = B_{21}u(\nu)$

And $B_{21}$ is called Einstein's Coefficients of spontaneous emission

then in some other topic, they wrote B₂₁ as probability of spontaneous emission per unit time.

Are they really same thing? ... I guess not ... B₂₁ should be something like probability of spontaneous emission per-unit Energy density (:p i know this doesn't make any sense ... ) ...

Please Help ...

 

[JeffKoch]

Spontaneous emission is nearly always written as A₂₁, not B₂₁ - B is used for absorption and stimulated emission. You can use dimensional analysis to find the units in the equation you wrote - what units must P₂₁ have?

 

[Redbelly98]

Hi all,
I was reading Lasers ...

By what author? Siegman? Milloni & Eberly? Other?

 

[cupid.callin]

Spontaneous emission is nearly always written as A₂₁, not B₂₁ - B is used for absorption and stimulated emission. You can use dimensional analysis to find the units in the equation you wrote - what units must P₂₁ have?

Oh yes, sorry i wasn't careful enough while typing ..

 

[cupid.callin]

By what author? Siegman? Milloni & Eberly? Other?

Its not from any book ... i pasted it from some website into MS word ... so i don't even remember the site ... :p